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1. 78 Ipt 3 amp H278 SEL INIT AUTOFEED STROBE POR OUT SEL ERR X X X t x CLPT OR 4 H20 lt gt amp H20 THEN GOTO 110 t x CLPT AND amp HFB H20 lt gt 0 THEN GOTO 110 Ipt x GOTO 130 ammer STOP RESETHI amp H1 MOSIHI LOW 0 MOSILO 0 er is OFF ogrammed and 170 amp H4 MISO amp H10 hit any key SET Circuit Cellar INK EEPROM storage The AVR microcontrol ler s big advantage is its in system programming As long as no external device is trying to drive the three I O bits the micro can be pro grammed or reprogrammed after PCB assembly And no special programming voltage is neces sary Programming the micro requires connections for V Gnd Reset and the three SPI control lines DEPARTURE INFORMATION The entire scoop on this and other AVR devices is on Atmel s web site While you re there check out the 49 AVR starter kit that includes an as sembler simulator and programmer demo board The AVR studio suite gets you from idea to prototype in a hurry Photo 1 shows the AVR starter kit along with this month s project a minimal cost programmer So why build a programmer when Atmel has such a great offer Well some people thrive on the insight that comes with hands on assembly Even if you take Atmel up on their offer as did when you re responsible for driving each control line through the proper algorithm you gain a special res
2. Adastra Systems 510 732 6900 Fax 510 732 7655 www adastra com LONWORKS GATEWAY ADAPTER Telebyte s Model 3201 transceiver is a PC l bus half card that enables a W indows 95 or W indows N T based PC to access a network operating under the LonW orks 78 kbps protocol which was developed by Echelon Corp The PC adapter supports plug and play for automatic detection and configuration by W indows 95 The gateway is implemented using the Neuron MC143150 processor running at 10 MHz The full 64 KB N euron address space is configured from dual port SRAM visible to both the PC and the Neuron chip A single I O portallows the PC to startand stop the N euron processor and enables a virtual service button N euron C programs developed with the Echelon N odeBuilder or LonBuilder may be loaded to the M odel 3201 with the supplied W indows 95 software driver The Neuron C program and a PC application may then communicate via shared memory The software package also includes a custom control O CX driver program for simple interface to Visual Basic Visual C C and similar languages The Model 3201 directly supports the 78 kbps free topology network and uses an RJ11 jack as the network interface Each unit includes a DIP switch on the rear bracket to provide termination for single or doubly terminated networks The Model 3201 sells for 288 Telebyte Technology Inc 516 423 3232 Fax 516 385 8184 www telebyteusa com Nou
3. SCG_HEADER AsyncData_I0 h 0 SCG_INCLUDE include D Workspace RtS generated code C Example AT_Command_Processor h SCG_INCLUDE SCG_FORWARD SCG_FORWARD SCG_CLASS 0 SCG_CLASS_INFO 0 class AsyncData_1 0 SCG_CLASS_INFO SCG_CLASS_PROPS 0 private Buffer InputCircularBuffer Buffer OutputCircularBuffer public Read_Terminal_Status ReadFromTermina const terminal_id ead_data rite_Status WriteToTerminal const terminal_id const write_data protected AT_Command_Processor rAT_Command_Processor DataManager rDataManager ErrorManager rErrorManager SCG_CLASS_PROPS 3 SCG_CLASS SCG_HEADER endif ifndef __AT_COMMAND_PROCESSOR_H define __AT_COMMAND_PROCESSOR_H SCG_HEADER AT_Command_Processor h 0 SCG_INCLUDE include d Workspace RtS generated code C Example AsyncData_l0 SCG_INCLUDE SCG_FORWARD SCG_FORWARD SCG_CLASS 0 SCG_CLASS_INFO 0 class AT_Command_Processor SCG_CLASS_INFO SCG_CLASS_PROPS 0 private CString LastATCommand public Get_Command_Status GetNextCommandFromTerminal const terminal_id read_data Send_Command_Status SendCommandsToOtherSubsystems const destination_id const send_command protected DataManager rDataManager ErrorManager rErrorManager DataManager rconfigures ErrorManager rconfigures SCG_CLASS_PROPS 3 SCG_CLASS SCG_
4. Here are examples of passing one or many parameters between C and assembly code routines CodeExample INPAR1 SET 12 Old Return Address SET 8 Old Frame Pointer Location VAR3 SET 16 var3 SET D2 VAR2 SET 12 SET D3 OUTPAR3 SET 8 OUTPAR2 SET 4 OUTPAR1 SET 0 LINK A6 28 OV D2 20 SP OV D3 24 SP OVE L 2 var3 i OV 4 var2 IMPORT _PassMany ADD L 2 INPARI FP OVE PARI FP OUTPARI SP OVE r2 QUTPAR2 2 SP OVE r3 VAR3 SP LEA SP AO OVE OUTPAR3 SP SR Many OVE L VAR3 SP IMPO _PassOne OVE PARI FP OUTPARI SP SR _PassOne var3 OVE L 20 SP D2 OVE L 24 SP D3 NLK A6 RTS Circuit Cellar INK SET 4 Offset relative to stack pointer long int var3 short int var2 var3 PassMany value 2 void CodeExample long int value Stack frame definition Offset relative to frame pointer optimize to D2 optimize to D3 var2 Establish stack frame Save nonvolatile registers 2 var2 4 var2 amp var3 Store variable Generate its address to pass Recover variable PassOne value 2 Destroy stack frame Recover nonvolatile registers Listing 8 Each different C array type requires a different underlying assembly language programming construct to implement char style4 Hello World short int style3 200 char DemoCode void long int stylel1 100 static short in
5. Po PERERERPEERPERE what pins and hex values should be used to program a controller but alas should the data be clocked in MSB or LSB On the rising edge or the falling edge On which edge should the reply data be read All we wanted was a simple inter face to attach to the parallel ports of our PCs and then at the DOS prompt to be able to type something like ISP MYPROG BIN Was it too much to ask DIGGING IN Clearly the burden of programming the controller is left up to the design engineer Unfortunately most PC o m a G Eo fE mie BEBREBE PART Lu fiat Figure 1 We couldn t establish reliable communications without a buffer IC under standably due to the TTL to CMOS connection The 74HC125 was convenient but any noninverting buffer will do programmers aren t up to the task of creating the hardware and most hard ware designers can t write the utility But despite the obstacles we created an interface to attach to the PC s parallel port and some software to download files to the 89S on the PCB HARDWARE Our first step was to try and directly connect the parallel port pins to the U1A 1 PaHCoo a 895X SERIES MICROCONTROLLER E parallel port has 12 readily accessible TTL outputs and 5 inputs The useful signals are shown in Table 1 Figure 1 shows the adapter needed to interface the parallel port of the PC to the Atmel ISP port We tapped 5 V from our ta
6. Pricing for tools and support offered with the eCos Partner Program starts at 3500 per engineering seat Cygnus Solutions 800 CYGNUS1 408 542 9600 Fax 408 542 9699 www cygnus com 8 Issue 101 December 1998 Circuit Cellar INK wT Xe 2 1e E NEWS POWER MANAGEMENT SUPERVISORS The IMP705 IMP706 IMP707 IMP708 and The 705 706 and 813L monitor the power supply and IMP813L low power microprocessor supervisor battery in microprocessor and digital systems A reset signal ICs integrate power supply monitoring and micro is generated whenever the supply voltage drops below 4 65 V for processor microcontroller watchdog functions into the 705 707 and 813L and bdow 4 40 V for the 706 and 708 compact eight pin MicroSO packages Besides In 1000 quantities pricing for the 705 706 and 813L is ensuring that the system microprocessor or micro 0 75 and the 707 and 708 cost 0 72 controller is adequately powered or has restarted properly after a power failure or brownout they IMP Inc integrate functions that monitor processor opera 408 432 9100 Fax 408 434 0335 www impweb com tion and issue system initialization signals when system failures or lockups are detected Each device generates a reset signal during powerup powerdown and brownout conditions A separate power fail detection circuit with a 1 25 V threshold checks battery levels or non 5 V supplies All devices have a manual re
7. Start Slave Address R W Ack Data Ack stoP Data Ack bytes of data 16 bits low byte first Pro Circuit Cellar INK Figure 2 SMBus relies on a basic message structure borrowed from the PC bus Issue 101 December 1998 43 current and predicted power avail abil ity and to set battery mode and alarm levels It also enables the host to set charging current and voltage levels for the smart battery charger Additionally it lets the system host interact with the smart battery selector to identify multiple battery availability The system host then uses all this information to establish a power budget that best meets user requirements SMART BATTERY The smart battery consists of a battery pack with embedded electronics that can hold smart battery data see Table 2 measure battery operating parameters and calculate and predict battery performance It can also monitor alarm conditions initiate and control battery charging algorithms and com municate with other SM Bus devices Placing SBS compatible electronics in the battery pack opens the door to a variety of battery chemistry indepen dent power management schemes for extending product runtime SBS based equipment users and power manage ment systems can access complete and accurate information even if the battery is changed The smart battery data tells the user how much longer a product will Quick Command Start S
8. functions The controller card provides the 12 and 5 V hardware interfaces to the LED and the power switch as well as an RS 232 serial interface to the terminal application The latter serial port has a few inherent attributes such as I O and IRQ addresses which can be entered into the System Architecture diagram Once the system engineers specify the system at an architectural level and initiate the System Architecture diagram the hardware developers can fill in the details of the boards and subsystems in the device e g 30 Issue 101 December 1998 memory I O and IRQ maps Photo 1 shows where the serial port for the modem is designed as a traditional PC style COM 1 The System Architecture diagram lets hardware engineers input critical information needed later by the soft ware engineers into the design to complete the system Such information includes identifying major subsystems connections and bus architecture as well as publishing memory I O and IRQ maps of the system Hardware related information lets software engineers undertake low level development like device driver develop ment without referring to hardware schematics or other documents gener ated by the hardware team The prop erties window as seen in Photo 1 enables hardware and software engi neers to access the same information used the System Architecture diagram to map the hardware of the system onto the software interfaces But to
9. little bus bandwidth and it addresses the needs of simple slave devices For example it can enable or disable backlighting in an LCD controller Send Byte commands address slave devices that need to receive only a single byte of data The 8 bit data byte holds a value of 0 255 This data can be interpreted as the slave sees fit For example a fan motor control can use this data to set motor speed or an LCD backlight controller may use it to set lamp intensity Receive Byte commands involve a single data byte too but the master reads the data from the slave The 8 bit data byte holds a value of 0 255 The interpretation of this data by the master is slave device dependent For example the data can indicate the temperature of the host CPU or the status of access door interlocks Write Byte Word is similar to Send Byte but involves a command code byte and one or two data bytes The command code byte tells the receiving slave how to interpret the following data The 8 bit data byte holds a value of 0 255 and the 16 bit data word holds a value of 0 65 535 For example the message can be the smart battery telling the smart battery charger about charging require ments The command code byte tells the receiving slave device that the data is the voltage level that the charger is to apply to the battery s terminals Read Byte Word is similar to Write Byte Word but it has a two step process The master must first write
10. to execute in a timely manner For the HC11 we chose a value of 2000 cycles per tick or about 25 us for a HC11 running with an 8 M Hz clock The default timeslice is five ticks or 125 us You may want differ ent values for your system INTERRUPT DRIVER Sometimes your program may need to perform some function at a regular interval and task scheduling may be too slow and unpredictable exec gives a hook to the timer interrupt handler if the global variable UEXC_Interrupt Diver is nonnull then it s assumed to contain the address of a function The system timer interrupt handler then calls this function before it per forms other work To use this feature assign the address of your function to be called to this variable TASK CONTEXT An important consideration is how to maintain the task s context so that exec can return control to a previously stopped task Because Wexec normally regains control through a timer inter rupt and that interrupt already saves the CPU states eg the register values Issue 101 December 1998 21 on the stack it is sufficient to only save the stack pointer of an inter rupted task at the time the handler was entered To resume a task exec reloads the stack pointer and uses the Return FromInterrupt instruction to restore control to the stopped task From a task s point of view a timer interrupt hits and some time later the interrupt handler returns and execution contin
11. trivially as CMOS switches that connect one of two reference voltages to its output Overall the circuit is a negative feedback circuit just like any other in that it tries to drive the error signal toward zero The inclusion of b the quantizer adds an interesting twist To analyze this circuit treat the quantizer and DAC together not as a nonlinear element but as a source of noise quan tizing noise l Il assume the sampler is operating below its Nyquist limit use the principle of superposition which lets me consider the inputs real signal and quantiz ing noise one at atime with the other input set to zero Figure 3b shows the circuit from the point of view of the sig nal source with the noise source forced to zero The integra tor basically becomes a low pass filter for the signal with a cut off frequency determined by its time constant Figure 3c shows the same setup from the point of view of the noise source The integrator is in the feedback loop which means that the circuit s output needs to be the derivative of the noise to drive the error signal to zero This condition means that overall the circuit is a differentiator or high pass filter for the noise If the noise generated by the quantizer is basically white or equal energy at all frequencies this circuit shapes the noise to empha size the higher frequencies and reduce the energy at lower frequencies numbered bins 0
12. 0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 Time units 12 16 20 24 28 FFT bin number Figure 2a This waveform has the same duty cycle as the one in Figure 1 b The spectrum has much less energy in the low numbered bins making it easier to filter Circuit Cellar INK 0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 Time units He m o o 12 16 20 24 28 32 FFT bin number Figure 1a This waveform has a duty cycle of 47 64 b However its spectrum is difficult to filter because of the excessive energy in the low Combining these results shows that the output of the quantizer is a one bit signal that contains a low pass version of the original signal plus high pass noise The final step is to consider the sampling flip flop at the output of the quantizer By driving this flip flop with a clock that is much higher 64x or more than the desired final sample rate you get a signal with the general properties discussed above N ext l II look at how this is applied to ADCs and DACs DELTA SIGMA ADC To create an ADC the deltasigma modulator is constructed in the analog domain see Figure 4a The input signal must be bandlimited to half of the flip flop s sample rate but since this is many times higher than the N yquist limit set by the final sample rate a relatively simple filter can be used often nothing more than a passive R C low pass filter The modulator is followed by one or more stages
13. Although his life was cut short by a car acci dent the spirit of Sey mour Cray lives on in the SV1 from Silicon Graphics The SV1 not only incorporates SIMD techniques but because SGI purchased Cray s company it is also upwardly compatible with his YMP As a classic vector processor the SV1 faces a different set of chal lenges For instance there s little concern with conventional benchmarks like SPEC The only goal is crunching through vectors at blazing speed and we re talking billions of operations per second One source of head scratching comes when vector ops and cache get in each other s way Vector data may not be reused and worse arrays i e vectors of vectors introduce the issue of stride For instance a column operation on a 256 x 1024 array calls for accessing every 1024 element which is contrary to the concept of locality i e the next access is near the previous one on which the cache concept is based Use Load Miss Use Load Miss Load Miss Load Miss Load Miss Use Use Load to Gr0 Instr Instr Instr Instr Instr Instr nsi Instr Instr nstr Instr Issue 101 December 1998 81 82 Issue 101 December 1998 Circuit Cellar INK Global prediction 40
14. Box 698 Holmes PA 19043 9613 Circuit Cellar INK makes no warranties and assumes no responsibility or liability of any kind for errors in these programs or schematics or for the consequences of any such errors Furthermore because of possible variation in the quality and condition of materials and workmanship of reader assembled projects Circuit Cellar INK disclaims any responsiblity for the safe and proper function of reader assembled projects based upon or from plans descriptions or information published in Circuit Cellar INK Entire contents copyright 1998 by Circuit Cellar Incorporated All rights reserved Circuit Cellar and Circuit Cellar INKare registered trademarks of Circuit Cellar Inc Reproduction of this publication in whole or in part without written consent from Circuit Cellar Inc is prohibited In System Programming Rewriting the Book Craig Pataky and Bill Maggs A Minimalist Multitasking Executive Richard Man and Christina Willrich Object Oriented Design of Real Time Systems A Multidisciplinary Challenge Irv Badr Some Assembly Required Assembling C Code for Your Embedded System Michael Smith Smart Battery Systems Ed Thompson 4 MicroSeries Digital Processing in an Analog World Part 3 Dithering Your Conversion David Tweed From the Bench Learning to Fly with Atmel s AVR Jeff Bachiochi Silicon U pdate Hot Chips X Files Tom Cantrell 48 Nouveau PC
15. Consider the presentation by Stanford Law School professor M argaret Jane Radin who expounded on the Basics of intellec tual property law with applications to the computer and electronics in dustries Too many lawyers try to cloak the eccentric aspects of our legal system in truth justice and highfalutin legal ese Not Ms Radin who freely admits that much of what passes for legal wisdom simply boils down to the foibles of human nature don t have time to go into the details of her four hour presentation itself condensed from 90 hours of classroom instruction N eedless to say the framers simple desire To promote the progress of science and useful arts U S Constitution Article 1 Section 8 has evolved into a morass of patent copyright trademark and trade secret laws As a 1s and Os man admit it s hard to swallow much of what the legal system presents as reason For example patents should describe a nonobvious invention in a way that specifically and particularly enables others to use it in the best way Ever tried to read a patent applica tion The real name of the game is X X X X X X XX KX K X KX XK X XK XK Figure 4 These days all hot chips employ SIMD techniques Motorola s AltiVec scheme goes beyond the usual intra element operations e g vms um instruction and adds inter element operations e g vsum instruction The result an inne
16. INFORMATION www circuitcellar com or subscribe circuitcellar com TO SUBSCRIBE 800 269 6301 or via our editorial offices 860 875 2199 GENERAL INFORMATION TELEPHONE 860 875 2199 FAX 860 871 0411 INTERNET info circuitcellar com editor circuitcellar com or www circuitcellar com EDITORIAL OFFICES Editor Circuit Cellar INK 4 Park St Vernon CT 06066 AUTHOR CONTACT E MAIL Author addresses when available included at the end of each article ARTICLE FILES ftp circuitcellar com For information on authorized reprints of articles contact Jeannette Ciarcia 860 875 2199 or e mail jciarcia circuitcellar com CIRCUIT CELLAR INK THE COMPUTER APPLICATIONS JOURNAL ISSN 0896 8985 is published monthly by Circuit Cellar Incorporated 4 Park Street Suite 20 Vernon CT 06066 860 875 2751 Periodical rates paid at Vernon CT and additional offices One year 12 issues subscription rate USA and possessions 21 95 Canada Mexico 31 95 all other countries 49 95 Two year 24 issues subscription rate USA and possessions 39 Canada Mexico 55 all other countries 85 All subscription orders payable in U S funds only via VISA MasterCard international postal money order or check drawn on U S bank Direct subscription orders and subscription related questions to Circuit Cellar INK Subscriptions P O Box 698 Holmes PA 19043 9613 or call 800 269 6301 Postmaster Send address changes to Circuit Cellar INK Circulation Dept P O
17. Normally a task function should not terminate i e it should execute an infinite loop If it does exec deletes it from the internal data structures Typically you create some tasks in your main routine and then start the scheduler running After that the processor executes your tasks and never returns to the main routine Each task needs its own stack which is supplied to the system when a task is created Unfortunately stack overrun i e when a task uses stack space that is beyond the range of the supplied stack can be a deadly problem exec checks the stack pointer of a task to ensure that it s within bounds but this check may not be of much value since a stack overrun may have already damaged important data includ ing pexec s internal data structures So it s best to be conservative and allocate a large stack for a task In fact if your system crashes mysteriously try allocating larger stacks for your tasks Stack overrun is a general problem in embedded programs M ultiple tasks exacerbate the problem because each task uses its own stack If there is only one control loop then all the functions execute with one stack and it is easier to be conservative with just that stack Unfortunately you have to pay the price for using a multitasking executive SCHEDULING AND TIMESLICE The scheduler chooses which task to run The period of time a task is allowed to run is called its timeslice Under exec tasks
18. after the code becomes stable Many optimizing compilers account for memory and register use by placing the originals directly into the outgoing parameter location when it offers a speed advantage Obviously this should only happen if the value isn t needed after the subroutine The com piler treats incoming and outgoing parameters as volatile variables int IsLightOn void register long int pt register long int temp register int rtnvalue define LAMPON 0x200 pt long int BASEADDR pt pt CONTROL temp pt rtnvalue 0 if temp amp LAMPO rtnvalue 1 Lamp is not on return rtnvalue When the variable s address is passed it s the address of the local variable on the stack that is passed The actual memory value must be pulled back into a register before use Parameters are promoted to long before being passed To gain speed the promotion of short int outpar2 to long in Listing 7 occurs in an implicit using MOVE W to an offset stack loca tion rather than an explicit manner EXT L followed by MOVE L Make sure your team doesn t assume the top 16 bits of the passed parameter are what s needed The out parameters of the calling subroutine become the in parameters of the called subroutine When pass ing parameters between C and assem bler it s important to understand the processor architecture associated with the call to subroutine instruction On a windowed process
19. an other microcontroller This feature permits logging or data forward and store func tionality in the emWare laden product To prove this result the emWare 8051 demo board uses an EEPROM to save A D values from a pot for later processing Oh yeah the PIC16C73 has an onboard A D module Hmm Looking further into the PIC 16C73 data book we find that the part is equipped with a USART universal synchronous asyn chronous receiver transmitter Ding Ding A quick look at emWare s capabilities shows us that emWare supports RS 232 Just leave out the S in USART and a USART smells like asynchronous RS 232 to me The PIC16C73 also has an internal programmable data rate generator The PIC16C73 is the right choice for first contact with emWare Besides all the things emWare requires this PIC can handle interrupts from internal peripher als as well as from the outside world The PIC16C73 contains an abundance of I O pins and an ample program and data storage area Just take a look at some of the advertisers in this issue and you ll see that programming the PIC is as easy as selecting a programming product from your company of choice THE CODE discussed Visual Caf in the previous installment Remember that before em Ware V 2 5 one had to code the HTML laced GUI With Visual Caf that task becomes much easier But won t dwell on Visual Caf here Instead I ll take apart a simple PIC emWare application l
20. and there s nothing you can do about it Once that PROM or OTP is soldered to the board your fate is sealed It s even worse if the final product is forever locked in a coffin of potting compound A latent design flaw ina datalogger may not show up for months No wonder firmware SEs are so jumpy Of course a lot of the pressure can be relieved if the target platform is in system programmable like a PC After all the IS department doesn t sweat with each tweak to the email system DIVERGENT DESIGNS Truth is the IS folks have long en joyed the luxury of instant reprogram mability because as far as a desktop PC is concerned code memory is the same as data memory and can be arbitrarily read written or executed from This design is called the Von Neumann or Princeton architecture On the other hand embedded con trollers have separate areas for code and data memory This design is re ferred to as the Harvard architecture The main reason microcontrollers have clung to the Harvard architecture is because by keeping data and code memory separate it s impossible for the machine to inadvertently corrupt its own code and go insane Unfortunately the strict Harvard architecture also prevents the micro controller from performing intentional code rewrites That s why so many technicians have spent so many hours swapping EPROMs Von Neumann designs are flexible but inherently unstable Harvard designs are rock so
21. applications and in creasing the component cost in the name of flexibility doesn t appeal to the end user After all shouldn t we get it right the first time Gulp LATEST REFINEMENT Responding to the need for low cost in system reprogrammability several manufacturers are equipping devices with built in rewritable code memory The key word here is rewritable Circuit Cellar INK Pin Direction Signal out control bit O out data bit 0 out data bit 1 out data bit 2 out data bit 3 out data bit 4 out data bit 5 out data bit 6 out data bit 7 i data bit 6 data bit 7 inverted data bit 5 data bit 4 control bit 1 inverted data bit 3 out control bit 2 out control bit 3 inverted 18 25 gnd Note that direction is relative to the PC 2 3 4 5 6 7 8 9 Table 1 The 25 pin parallel port is standard on all IBM compatible PCs and offers 17 pins capable of doing useful work 12 outputs and 5 inputs In system programming ISP has been around for many years but only in OTP devices But Atmel and Dallas are already shipping production quan tities and similar products are soon to follow from Microchip and Philips This means the days of socketed EPROMs masked parts and OTPs are gone N ow you can solder a control ler directly to the PCB and program it just before shipment More importantly you can reprogram that same controller ATMEL ISP Now wed like to narrow the focus to the A
22. are run to com pletion of their timeslices unless they are explicitly yielding control to the Listing 2 This program is the same as in Listing 1 but it is partitioned into separate tasks The control loop is part of the multitasking executive Task Task Task Task Task Task check sensor 1 check sensor 2 compute pi to 347 digits contemplate and meditate activate death ray 1 drive motor Circuit Cellar INK system or hogging the processor for another timeslice Although exec doesn t assign priorities tasks can have different timeslice lengths so you can cause a compute intensive task to run longer if necessary The main purpose of the exec con trol system then is to interrupt the processor at the end of a task s time slice and invoke the scheduler to choose another task to run exec uses a timer to interrupt the CPU at regular intervals Almost all microcontrollers have timer interrupt functions that can be used for this purpose For example on the HC11 there are five timer registers each one of which can be set up to generate an interrupt when the timer register s value matches the value of the free running timer counter The time period when such an interrupt occurs is called a tick and its timeslice is some multiple of ticks A tick s value should be chosen such that the processor is not inter rupted too frequently but it shouldn t be so long that other tasks do not get
23. block oriented device using the losetup utility and the loopback device dev loop0 dd if dev zero of initrd img bs 2b count 1204 losetup dev loop0O initrd img mkfs dev loop0 mount dev loopO mnt create 1 MB file map file to loopback device lay down a Linux filesystem mount the ramdisk image mkdir mnt bin mnt dev mnt etc mnt lib create some directories cp a dev console mnt dev cp a dev systty mnt dev cp a dev ram mnt dev cp a dev ttyl mnt dev cp a dev tty2 mnt dev cp a dev tty3 mnt dev cp a dev tty4 mnt dev cp hello mnt bin echo bin hello gt mnt profile cp bin ash static mnt bin sh umount mnt losetup d dev loop0 gzip lt initrd img gt initrd mcopy autoexec bat loadlin exe vmlinuz initrd a CIRCUIT CELLAR INK DECEMBER 1998 create devices program to run create Linux startup file static version of shell unmount the image unmap file compress it copy everything to floppy Photo la In the kernel configuration utility each section covers an area in the kernel and clicking ona section brings up a detailed panel with options to select b lIn this subsection of the con figuration utility you click oneach item s radio button to include the feature either statically in the ker nel y or n Many features can also be configured as a loadable kernel module m 56 CIRCUIT CELLAR I
24. compiler handles global names For example some compilers prepend an underscore before a global name if it s to be used by an assembly module but these differences are easy to handle 22 Issue 101 December 1998 Listing 3 The key data structure of a multitasking executive is its task control block uexec s task control block is described here as a C structure enum T CREATED T_READY typedef struct TaskControlBlock struct TaskControlBlock next igned char tid ed char state ed char t ed c xfunc void ed char stack_start ed char stack_end ed char sp icks ar current_ticks number of ticks remaining TaskControlBlock INTERRUPTS Interrupts must be carefully enabled and disabled inside exec If this is done improperly unpredictable results occur For example if interrupts are left enabled while global data structures are being manipulated a data structure may bein an inconsistent state and further accesses in an interrupt handler will crash the system Of course if interrupts are inadvertently disabled when resuming a task the timer inter rupt is also disabled and multitasking will stop A simple enhancement is to use the watchdog timer presented in most microcontrollers to detect these kinds of system crash errors However you need to have a mechanism for the system to either restart itself or report the errors TASK CONTROL BLOCK The data structure Tas
25. complete the mapping of the hardware onto the multiple tasks in the software architecture need the Concurrency diagram In Figure 7 the Concurrency diagram shows the tasks identified for my modem inside the modem controller card and DSP board The serial data task exchanges data with the serial ISR through the packetized data chan nel Serial data bidirectionally feeds the data to AT commands and error correction tasks through channels using event flags as notification mechanisms Each task or ISR may be mapped to one or more software object architecture using one addi tional step inside the Concurrency diagram The tasks must be mapped to the objects in the Class diagram from Figure 8 In this case the Serial Data ATCommands DataCompression and ErrorManager tasks are mapped to AsyncData_I 0 ATCommand Processor ErrorManager and DataManager classes respectively Similarly DSP Manager task is mapped to the DataPumpController class By mapping tasks to their represen tative objects the software architecture and object architecture layers are bridged The detailed design of my system means the relationships can be traced from the hardware into the multiple tasks and storage and all the way to the objects all without dis solving the boundary between the system hardware software and the object architecture EMBEDDED UML As the adoption of OO technology in the workstation software industry has increased the
26. embedded market has slowly followed suit Although many projects still employ structured analysis techniques a majority are planning the switch to OO technology As the trend continues toward UML notation most OO embedded projects are sure to follow was recently involved in designing a hemodialysis machine at Aksys Ltd a company that specializes in home dialysis In addition to control software interfaces For example the serial ISR in Figure 7 is mapped Serial ISR Serial interface to the serial interface which is mapped to the RS 232 interface in the System Architecture diagram as shown in Figure 6 The Concurrency diagram Data can be used to map hardware available elements to the software archi tecture This layer includes most importantly the RTOS or the multitasking entity as well as the data storage elements To continue the mapping process the software architec ture can then be mapped to the Circuit Cellar INK Bidirectional packetized data Data stream 4 i Configure Configure EC DC Error manager P compression Bid intermedia data Bidirectional final data DSP manager Telco Figure 7 A Concurrency diagram lists the tasks or the processes in the system Also shown are the messaging elements software interfaces and interrupt service routines SerialDriver CommandProcessin
27. entry point routines are mixed EXPORT _ResetDevice In asm s used address register AO one of the limited processor resources During ResetDevice the original value held in this address register was destroyed to access the hardware con trol register via an instruction with a convenient indirect addressing mode ResetDevice _ResetDevice void ResetDevice void ResetDevice pt SET AO MOVEA L BASEADDR pt MOVE L RESET CONTROL pt RTS register long int pt pt long int BASEADDR Reset Control register 34 Issue 101 December 1998 Circuit Cellar INK Nonvolatile registers Volatile registers SDS Compiler DO D1 AO A1 D2 D7 A2 A6 SP Table 4 The designation of volatile and nonvolatile registers is an arbitrary convention that depends on available processor resources and the balance consid ered appropriate by the compiler developers On some windowed RISC processors e g SPARC you can have many volatile and nonvolatile registers for general programming use and still have other registers available for spe cial OS related operations Other processors offer fewer opportunities Table 4 shows the volatile and nonvola tile register allocations for the SDS 68k C compiler and similar arbitrary selections found with other compilers RETURNING PARAMETERS Many functions return a parameter and because the parameter is typically used in the calling routine it m
28. functions exported on the device tax is funcName Extended Attribute Normal Attribute tended Attributes CEXT functions supports streams CNONE ormal Attributes F BIT input is a bit value BYTE input is a one byte Value DOUBLE input is a double precision floating point value DWORD input is a four byte value FLOAT input is a floating point value E no input REA input i stream of data RING input i one byte character array RING input i two byte unicode character array D input i two byte value RING input i two byte wide character array BIT returns a bit value BYTE returns a one byte value TDOUBLE returns a double precision floating point value DWOR returns a four byte value FLOAT returns a floating point value NONE does not return anything ETSTRE returns stream of data ETSTR returns one byte character array ETUST returns two byte unicode character array WOR returns two byte value WST returns two byte wide character array Attributes can be combined by ORing the keywords FUNCNONE FUNCINBYTE FUNCRETWORD HH Mmm nmmn ne a a Sl a eo am an a a aa a T ee o eceeeeaaeaeaaqcae cececeeceec PDDADDDDADAA DD T 5 4o33 OoOOOOOOOOOOONDOOOOOOOOOO O o h a S K g CNONE FUNCINBYTE CNONE FUNCINBYTE a gt m7 0 c VARS Defines variables exported on the device Syntax
29. hope things are a little clearer for you as you use these technologies in your projects To get more information on various converters high end delta sigma and high speed check in with AKM Semi conductor Crystal Semiconductor part of Cirrus Logic and Analog Devices And to learn more about dither my MathCad worksheets demonstrate how the different PDFs perform and enable you to play with the parameters David Tweed has been developing hardware and real time software for microprocessors for more than 22 years starting with the 8008 in 1976 His system design experience includes computer desi gn from supercomputers to workstations microcomputers DSPs and digital telecommunications systems David currently works at Aris Technologies developing digital audio watermarking You may reach him at dtweed acm org SOFTWARE MathCad worksheets for this article are available via the Circuit Cellar web site REFERENCE 1 D E Knuth The Art of Computer Programming Vol 2 Seminum evical Algorithms Addison Wesley Reading MA 1997 SOURCES Converters AKM Semiconductor Inc 888 256 7364 408 436 8580 Fax 408 436 7591 www akm com Cirrus Logic Crystal Semiconductor 800 888 5016 512 445 7222 Fax 512 445 7581 www cirrus com Analog Devices Inc 800 262 5643 781 937 1428 Fax 718 821 4273 www analog com Circuit Cellar INK Issue 1
30. how to program in assembly language is know when not to program in assembly language Among the many valid reasons for such advice value for time and effort should strike home with the industrial programmer It takes about as much time to develop debug test integrate and maintain one line of code in any language so the best value is obtained by coding with the highest abstraction possible If a picture s worth a thou sand words then often a line of C is worth a hundred lines of assembly code C was designed as an efficient processor independent assembly lan guage So many constructions behind the language translate into special features available in a processor s instruction set C C constructs e g or opera tors reflect the typical processor in struction where the destination is identical to one of the sources In the good old days we used C to take advantage of these special features because compilers were rather unso phisticated But today s compilers are as good as and frequently better than an assembly language programmer For instructions using CONST lin Table 1 most compilers generate the faster increment instruction Most modern C compilers analyze your code and automatically handle a number of optimizations to account for speed and memory trade offs Table 2 shows some of the switches available on the Software Development Systems SDS compiler Of course you may have to tweak som
31. initialization constants in ROM and copy them into the variables as part of the ResetInit routine used in init s see Listing 2 Other C array conventions can sneak up and bite the unwary You must allocate for the end of string character at the end of a string array and then remember to pack the array style4 with additional NULL characters so the next integer array style3 allocated within the code starts at the proper word 16 bit or long word 32 bit boundary KEYWORD VOLATILE already discussed the difficulties of pointer arithmetic when using C to access hardware registers An equally serious problem occurs when you want to access a hardware register within a loop Consider using this code to generate an average of eight readings of a hardware input register long int pt 0xA0000 long int sum 0 for count 0 count lt max count sum pt sum sum gt gt 3 I le 5 Q a 5 ct An optimizing C compiler may rewrite this code into a form equivalent to long int pt long int 0xA0000 long int temp long int sum 0 temp pt sum temp max gt gt 3 pt always accesses the same memory location so the same value should be returned Bringing all constants outside the loop can optimize the loop This as sumption is valid if standard memory operations are performed But here the pointer accesses a hardware register whose value may change Listing 7
32. interest The rush toward Internetivity is predictable don t anticipate a stampede but effective demonstration of the technology will surely expedite its incorporation We continue to see our roll as an application resource that provides such demonstration We have a number of embedded Internet related projects in the works Among them is a contest winner from our Design98 contest for a single chip Internet connected appliance We trust that the strength and support of Motorola along with 45 000 in cash prizes for Design99 will incite the design bug in all of you look forward to seeing your innovative Internet connected projects among the entries for Design99 steve ciarcia circuitcellar com See 96 Issue 101 December 1998 Circuit Cellar INK
33. is taken low and after applying power A program ming enabled command sequence must be the first command clocked into the part using SCK and M OSI Each command is four bytes long aer 14 0 m Hou td svalue for stack pointer put it there va for PORTB xxxxx111 put it there va for PORTB direction xxxxxIOI put it there skip if CFG0 PBO 0 jump PBO 1 1 iv O a ov D DI gt am i am skip next if CFG1 PB2 0 TELD G33 NO OO T CO nOEOoUMmomum aoo oJ pD The minimum times for SCK is two MNP ERE crystal cycles high and two crystal ldi sreload count for 1 s cycles low using a 4 M Hz crystal ldi y Paar ld that s 500 ns minimum rjmp jump The micro outputs the bytes sent CFG_OL to it using its MISO pin The output ldi sreload count for 1 min bytes are delayed by one byte from the input j jump For instance if you send the four wae z sk t if CFG1 PB2 0 bytes 60 01 0C 12 write 12 to address ee ee 010Ch low byte then you would get 10 back zz 60 01 OC zz is the last byte sreload count for 1 h from the previous command There are exceptions to this rule j T jump When asking for information from the micro reading the last byte returned is the data from the micro As in 20 01 OC xx reading the low byte from 01 OC s reload count for 1 day value for 64 prescaler where xx is
34. of digital low pass filtering which simul taneously reduce the sample rate and increase the usable precision of each sample Because these filters are digital it s relatively straightforward to implement nice stable linear phase FIR filters with steep skirts to eliminate aliasing 32 Issue 101 December 1998 69 Quantization noise Sample af clock Difference Integrator Quantizer 2n T 1 iy f Sampler DAC two levels Error signal Figure 3a The delta sigma modulator forms the basis of analog to digital and digital to analog converters b From the point of view of the input signal the integrator creates a low pass filter c A high pass filter is created for the quantizer noise To understand how the modulator s one bit samples are converted to multi bit output samples look at Figure 4b It reviews the basic structure of a finite impulse response FIR digital filter The samples are fed through a series of delay stages at the top which in this case are simple flip flops Each sample is multiplied by one of the FIR coeffi cients and since the sample is either zero or one it s just a question of whether or not the coefficient gets added to the final sum at the bottom If we want an output precision of n bits and there are 2 stages in the FIR filter there will be up to 2 coefficients in the sum So each coefficient needs to have at least n m bits of precis
35. on the spec trum of the signal other than to remove images between the original Nyquist limit and the new higher sample rate The digital implementation of the modulator consists of a subtractor that creates the error signal an accu mulator adder and register that per forms the integration and a quantizer stage that consists of little more than taking the most significant sign bit of the accumulator D S Modulator The higher sample rate reduces the magnitude within the band width of interest of the sin x x error introduced by the zero order hold effect covered in Part 1 This effect is dealt with by having a switched capacitor filter at the output of the quantizer that has a slight rising slope in the pass band The overall response is generally flat to within a few hundredths of a decibel The signal is passed through a simple one or two pole low pass filter that is external to the DAC chip This filter removes the high frequency image as well as most of the quantization noise WHY DITHER In Part 1 discussed the noise cre ated by the quantizing process Under most circumstances it has the charac teristics of white noise But you saw how it can be strongly dependent on and modulated by the input signal which has objectionable consequences One common example occurs with audio converters When very low level signals are being digitized only a few bits out of the ADC s complete range are used a
36. option Part of the ISP operation is keeping the micro controller in a reset state for the dura tion of the programming cycle The default operation of the ISP utility holds the reset line high while program ming but the r option was provided in case you ve interfaced your micro controller s reset line through an in verting buffer of some kind HEX2BIN Most of the 8051 compilers we ve used generate only a hex file and not a binary file Intel hex was originally created to make our generated files easier to view and transport But processor cores prefer the true binary opcodes and data to ASCII codes If your compiler generates a binary file use it If it generates an Intel hex format file we also provide a HEX2 BIN utility to perform the conversion Type HEX2BIN myfile hex andthe appropriate translation is made Program code memory with the indicated file Program nonvolatile data memory with the indicated file Table 2 Some ISP command line options are provided to make the utility generic while others are designed to accommo date the programming variables that may exist Set programming speed 0 being fastest Display all the commandline options HITTING THE MARK We ve covered broad design consid erations as well as specific solutions Even if Atmel is not your style several manufacturers are likely to be sampling similar solutions by year s end As you know the winners in this business are ligh
37. over the interrupt vector The PIC16C73 can be interrupted onan A D conversion serial communica tions event timer event capture event or change in I O port status So it could be important to keep the interrupt vector area coded for such possible events if your program is so inclined Beginning at the label loop0 the same sequence of events takes place as with the 8051 version of EMIT This obser vation is also true for all other devices All micros need some type of initialization that prepares them for the task at hand Here the first call is to the Init MicroController subroutine Listing 4 Listing 5 Here s a good example of how the PIC spins the pins InitPortc PORTC is a multifaceted port supporting I 0 for several onboard peripherals bit pin name 0 RCO T1OSC T1CKI RC1 T1OSI CCP2 Timerl 1 0 Timerl Capture Compare I 0 RC2 CCP1 Capture Compare PWM 1 0 RC3 SCK SCL SPI i2c 1 0 RC4 SDI SDA SPI i2c 1 0 RC5 SDO SPI 1 0 RC6 TX CK 0 USART RC7 RX DT I USART ay using these pins output i 0 I input T tristate input output Clrt PORTC pagel movlw B 001 O outputs SCL 12C clock gt SDO Serial Data Out UART TX gt UART RX lt movwf paged return DECEMBER 1998 LAED C details the first call in this subroutine The first job is to transfer the calculated data rate value to the data rate register SPBRG If you re new to PIC
38. t send in the marketing reps but who want to talk to us directly about their latest projects And know you want to hear about them single chip embedded Internet platforms the 1451 2 standard ASIC how tos motion control and there are so many more Thanks to all of your input know 1999 is going to be even more spectacular elizabeth laurencot circuitcellar com 2 Issue 101 December 1998 Circuit Cellar INK CIRCUIT GELLAR THE COMPUTER APPLICATIONS JOURNAL ASSOCIATE PUBLISHER Sue Skolnick CIRCULATION MANAGER Rose Mansella CHIEF FINANCIAL OFFICER Jeannette Ciarcia ART DIRECTOR KC Zienka ENGINEERING STAFF Jeff Bachiochi PRODUCTION STAFF Phil Champagne John Gorsky James Soussounis PROJECT EDITOR Janice Hughes EDITORIAL DIRECTOR PUBLISHER Steve Ciarcia MANAGING EDITOR Elizabeth Laurencot TECHNICAL EDITORS Michael Palumbo Rob Walker WEST COAST EDITOR Tom Cantrell CONTRIBUTING EDITORS Ingo Cyliax Ken Davidson Fred Eady NEW PRODUCTS EDITOR Harv Weiner EDITORIAL ADVISORY BOARD Ingo Cyliax Norman Jackson David Prutchi Cover photograph Ron Meadows Meadows Marketing PRINTED IN THE UNITED STATES ADVERTISING ADVERTISING SALES MANAGER Bobbi Yush 860 872 3064 ADVERTISING COORDINATOR Valerie Luster 860 875 2199 Fax 860 871 0411 E mail bobbi yush circuitcellar com Fax 860 871 0411 E mail val luster circuitcellar com CONTACTING CIRCUIT CELLAR INK SUBSCRIPTIONS
39. the standard OPC interface elements in W indows CE and W indows NT The O DK operates within the popular M icrosoft Visual Studio on W indows N T 4 0 and includes DeviceCOM server libraries a DL compiler sample applica tions deployment utilities online documentation and tutorials The O DK also includes 20 DeviceCOM server run time licenses for development or small deployment purposes DeviceCOM runs on Windows NT 4 0 and on all supported processors for W indows CE 2 0 and 2 1 The core DeviceC O M server occupies about 300 KB of memory or less depending on the target processor The DeviceCOM Quickstart O DK V 1 0 sells for 1495 Run time licenses below 3 are available for volume applications and a 5 V only power requirement A prototyping area permits extra hardware to be added easily by means of clearly labeled access to buffered PC 104 data address lines decoded control signals SPI circuitry and support for both through hole and surface mount devices All module data variables 1DY V 01 11 V BY yV e1 1 0 0 and parameters are stored ina RAM arrangement that the host accesses via a sequential FIFO interface N o special drivers are needed since the module accepts standard I O commandsfrom DOS and Windows programs The lO C P 74 is fully programmable using readily available PIC develop ment tools The assemblyanguage source code for the preprogrammed factory default configuration is pro vided royalty fre
40. to a stop Up ahead an ambulance was pulled off to the side doors flung open On the scene one emergency medical technician was trying to revive the accident victim while another monitored vital signs with portable medical equipment Since had nowhere to go sat attentively considering the event before me wondered how this life saving equipment is maintained despite the rigorous treatment it receives from always being on the go How do they know battery power won t fail at a critical moment like now SBS TO THE RESCUE M aybe the answer can be found in technological advances brought about in the computer and telecom industries where intense activity surrounds power management for portable systems Our desire to edit one more docu ment or place one last telephone call has led us to demand more staying power from laptops and cell phones Developments that extend performance reliability and safety in computers Circuit Cellar INK and telephones are being adopted in the variety of electronic products that we depend on daily From semiconductor companies to software houses component manufac turers to system integrators a plan was developed to combine information and communications within a system of portable power related components The result the Smart Battery System SBS This article introduces the SBS standard for implementing smart battery technology and suggests the improved performance reliabil
41. tricks now includes big caches superscalar multi instruction speculative and out of order execution branch prediction SIMD vector ops and so on The art of computer archi tecture involves choosing the right combination and finessing the details Cache wise bigger is always bet ter For instance the latest version of Photo 1 BM s Deep Blue the first computer to win a match against a world chess champion is an IBM RS 6000 based system with 30 boards each containing 16 of the custom accelerator chips shown here HP s Precision Architecture PA the PA 8500 in Figure 1 includes a whopping 1 5 MB of cache 0 5 MB of Dual 64 bit integer ALUs instruction 1 MB of data Given HP s long time posi tion in favor of off versus on chip cache such a devel opment is even more no table Fact is with tens of millions of transistors to find homes for big cache is the easiest way out Besides making cache bigger the goal is to build and use it smarter Even if half a dozen instructions can be found to keep all those can become a bottleneck Thus the trend towards nonblocking designs escalates when a cache miss happens don t just sit there twiddling your thumbs try to execute another instruction The latest designs allow dozens or even hundreds of cache accesses to be pend ing without stalling the processor As for using cache more intelligently the earlier trend towards software
42. ues The fact that other tasks get a chance to execute while the task is stopped is invisible to the task There is one additional place where the task context must be saved when a task voluntarily gives up control using the UEXC_Defer function In this case UEXC_Defer constructs an inter rupt stack frame so that no special case handling is needed to resume the task This scheme doesn t work with processors using a separate interrupt stack from the user stack Also if a multitasking executive provides re source waiting functions semaphores mailboxes etc there are other places where task context must be saved In these scenarios it s simpler to save the entire CPU context in the task data structure and not rely on the interrupt stack Since exec does not provide resource waiting functions and since most small microcontrollers don t use a separate interrupt stack using the interrupt stack frame to save the task s context is fast and effective CODE COMMUNICATION Most of the exec routines are written in C A small number are in assembly mostly to manipulate inter rupt stack frames The format of passing arguments between routines is compile dependent so we opted to use global variables to pass information between the assembly and C routines of course C routines calling other C routines use the stan dard C calling format Only two dobal variables are needed There are some minor differences in how each
43. via your Internet connection And instead of dull old command line you have control via a custom GUI But the real story is that by using the Internet and some RS 232 you can apply EMIT to most anything requiring human interaction A simple PIC program coupled with the magic of emWare proves that it doesn t have to be complicated to be embedded APCEPC Fred Eadly has over 20 years experience as a systems engineer He has worked with computers and communication sys tems large and small simple and com plex His forte is embedded systems de sign and communications Fred may be reached at tred ed p com SOURCES PCM 4862 American Advantech Corp 408 245 6678 Fax 408 245 8268 www advantech usa com SDK 2 5 emWare 801 256 3883 Fax 801 256 9267 www emware com PIC16C73 Microchip Technology Inc 602 786 7200 Fax 602 899 9210 www microchip com DEPARTMENTS Digital MICRO 68 MicroSeries Processing in TL From the Bench an Analog David Tweed World Dithering Your Conversion SERIES 80 Silicon Update o far I ve cov ered some of the basic issues relating to conversions and dis cussed the relative merits of various Now that converter technologies This month wrap up by covering two more advanced topics delta sigma we ve got s converters the latest rage in ADCs the basics and DACs and dither what it is why of A D and D A con you might want to use it and how t
44. 01 December 1998 73 FROM THE BENCH Jeff Bachiochi Learning to Fly with Atmel s AVR Just because Atmel s new AVR ee wih ii micro has 118 instructions don t let that get you bogged down They re grouped into four easy classifications and the whole AVR line can be programmed into 16 bit address space 74 Issue 101 December 1998 s many of you know I m a crash and burn programmer admit it like the cause and effect control it gives me Lately with some of the improved simulators I ve run some level of simu lation before programming a chip But there s nothing like adding a touch of hardware even if it s a toggling I O pin to help with software debugging On top of my debugging list are those little ceramic windowed micro processors These erasable parts need time under the UV lamp whenever want to make a change in the code remember paying a few hundred dollars for one of these in the early 80s Today they re not as expensive but they re pricey enough that you Photo 1 Aimel s low cost programmer complements a suite of useful tools pack aged my minimum parts programmer in a dongle enclosure shown behind the Atmel board Circuit Cellar INK generally don t find them hanging around the workbench Fixing the code between each crash and burn never takes much time It s usually one of those dolt typo things But the UV lamp manipulates the pro
45. 96 x 2 Choice prediction 4 4096 x 2 yo Path history Prediction Local prediction history Local 1024 x 10 1024 x3 Program counter Figure 3 When it comes to branch prediction the Alpha 21264 considers both the past behavior of the branch and the path taken to arrive at the branch In fact it s amusing to construct mental cache buster exercises Choose the worst case combination of algo rithm data layout cache size and organization and the grandest chip is reduced to a quivering sliver of silicon Considering locality and the desire to exploit the burst characteristics of DRAMs most caches use long dozens or hundreds of words line lengths When a miss occurs the controller loads a complete line presuming that the penalty for extra transfers is offset by the likelihood of subsequent accesses within the same line But an ugly mismatch of algorithm stride and cache may result in a com plete line refill for each array element access You d be better off chucking the cache altogether The SV1 addresses the situation with a 128 KB streaming cache design that has short lines only 8 bytes is very nonblocking up to 192 pending references and delivers at 4 GBps CHESS CHIP You can always count on Hot Chips to deliver a bit of technical whimsy this time in the form of Designing a single chip chess grandmaster while kn
46. BS compatible electronics in the battery pack the charger can be reduced to a slave device that supplies charging voltage and current to the bat tery independent of battery chemistry SMART BATTERY SELECTOR The selector provides the data and functionality to support multiple smart batteries in one system It also commu nicates with other SBS devices over the SM Bus The selector maintains configu ration data provides system power switching battery charge switching and has SM Bus communication capabilities Name ManufacturerAccess RemainCapacityAlarm RemainTimeAlarm BatteryMode AtRate AtRateTimeToFull AtRateTimeToEmpty AtRateOK Temperature Voltage Current AverageCurrent MaxError RelStateOfCharge AbsStateOfCharge RemainingCapacity FullChargeCapacity RunTimeToEmpty AveTimeToEmpty AveTimeToFull ChargingCurrent ChargingVoltage BatteryStatus CycleCount DesignCapacity DesignVoltage Specification Info ManufacturerDate SerialNumber ManufacturerName DeviceName DeviceChemistry ManufacturerData Description Content determined by battery manufacturer When RemainingCapacity falls below this value battery sends AlarmWarning to SMBus Host with REMAINING_ CAPACITY _ ALARM bit set When AverageTimeToEmpty falls below this value battery sends AlarmWarning to SMBus Host with REMAINING_TIME_ALARM bit set Controls battery operating modes and reporting capabilities Sets charge or discharge rate fo
47. HEADER endif Circuit Cellar INK Issue 101 December 1998 29 Terminal Application Asynchronous modem Modem controller RS 232 rH 12V I Local 5V Status LEDs DS board P Local Analog port Analog subsystem DAA t Telco Figure 6 At the System Architecture level all the major hardware elements of the modem along with the hardware and software interfaces can be mapped on the System Architecture diagram hardware This mapping allows a much cleaner class design UML FOR DETAILED DESIGN When modeling for high level design several additions were made to the traditional UML notation to support real time systems better and to im prove coordination Similarly the UML can be extended to represent the de tailed system design while keeping the diversity of the development team in consideration To support the hardware layer in Figure 5 a new set of notations is achieved via the System Architecture diagram Figure 6 shows the cards and the interfaces in my modem The modem controller card hosts the AT command processor as well as the data compression and error correc tion software subsystems The DSP board is a different processor card responsible for implementing digital filters and other signal processing
48. IT places data into the pay oad buffer area and then makes acall to the desired function which places any data to be returned in replydata EMIT picks up this data and applies it to a variable that is represented by a GUI widget in the web browser window Listing 8 is an excerpt from the config ini file that shows how the var iables and functions are defined to EMIT CIRCUIT CELLAR INK DECEMBER 1998 THE RESULTS designed a web browser interface connected EMIT widgets to real functions and variables ona PIC16C73 and looked at or changed PIC internal register values lt may not seem like much until you con sider can do this from anywhere Unfortunately EMIT was chained to the 8051 platform for a long time Al though the 8051 is great it s fun to exploit the myriad of onboard peripherals found in PIC products For instance you could take my appli cation and include the use of the eight A D inputs or apply the IC interface to communicate with other equally equipped intelligent devices With Visual Caf you can create a user friendly interface and connect variables and functions to code in the target PIC Another plus is the ever increasing internal code space and register or RAM area EMIT functions normally reserved for a PCM 4862 can be moved to the target microcontroller leaving more room on the embedded PC for utilities or applications As for applications imagine control ling gadgets in your home remotely
49. NK DECEMBER 1998 a Lees tae Coe pesto b Gereral seba Taim amr bel r gt F is te rt vllo ze mf rarat math oration wa IP e Fa v nl networking suore i Fimma TE mi ter hiri cirar we lie on eiet mru to Jon ra Hala imb miam Feall press Hale EA s a l BCD bie apport NF imr inaj ijara at fil ye 2 on PCI bridge opis ieet san Gireno He Lo fred mia coed yla won Sates Y PE Halp ME singi r T i T 1 r z 7 REEERE A ulse a n armel support for avout hiraries Hain viene bll h Karnal appar fier Iu borer Le Hale t f Geer vie w g ye E n kamal mppori for iii borer ie Halo l Combe aral ad F F a OCT da BF etn Lo m EZE tte jg ies ruit imir mrmi ir iie Gii Added Tray Hers Geet ipestome s Fide Hain Mru Heer Pren LiLo how to construct the table and how to label each boot entry A typical configu ration file is shown in Listing 1 The configuration file contains some general information about which drive to install the boot loader onto and where to put the table on the disk To install the loader run 1i10 Ofcourse anytime you muck around with the bootblocks ofa disk drive it s always wise to backup the contents of the drive first You can also use LiLo for a Linux boot floppy To do this use a desktop system which serves as the development system Insert the floppy and install a Linux file system Assuming the floppy
50. PIC remotely you need some sort of communications port I m partial to Ethernet but you can t plug an NE2000 compatible ISA or PCI card into a PIC An Ethernet implementation using PIC code and some Ethernet interface hard ware is one way to go but it entails some complexity that ruins the whole point of using the PIC The answer is simple As mentioned last time emWare can communicate using many of today s com mon protocols Although Ethernet could be used here it looks like it isn t the best choice It would take a very long category 5 cable to control the PIC once it left the Florida Room bench Taking a look at the communications resources offered by the PIC16C73 we find a synchronous serial port SSP that can operate in two modes Serial Periph eral Interface SPI and Inter Integrated Circuit I C 59 SPI mode is a syn chronous based protocol that can operate as a full duplex connection Although it s possible to write any type of communications driver for enWare the synchronous part of SPI would present mobility problems as you d need the right hardware software ISP combination to talk to the PIC via the Internet SPI is primarily used fo talk to serial EEPROMs and the like Similarly IC isn t used much off its native PC board but rather in an applica tion that requires the chips to talk This could be a plus In fact SPI and I2C can both be used to talk to an EEPROM device or even
51. So you can enjoy the benefits of a multitasking executive without paying alot in cost or resource consumption This article first gives a high level description of exec including some Listing 1 This sample embedded program uses a control loop Each time through the loop several tasks are done in sequence Control loop check sensor 1 check sensor 2 compute pi to 347 digits contemplate and meditate activate death ray 1 drive motor goto control loop of the design choices N ext we describe the data structures followed by API functions and assembly routines M ost porting efforts are only needed in modi fying the assembly routines so skip to that section if you re interested in porting exec to your favorite micro controllers or compilers The last section gives a summary and ideas for enhancements If you just want to use exec see the API descrip tions for the interface functions Under exec a task runs for a period of time until a timer interrupt inter rupts it and the exec control system chooses another task to run This pro cess repeats indefinitel y at least until the system crashes or interrupts are accidentally disabled or the embedded system runs out of battery juice TASK FUNCTION A exec task is a C function that does not take an argument or return a result Any such function can be made into a task via UEXC_CreateTask Tasks can be created and killed dynamically even within other tasks
52. When mixing C and assembly code functions never use int variables specify long int when intend to manipulate 32 bit variables and short int for 16 bit variables also state the size of the variable being manipu lated in each assembl y language in struction MOVE L and MOVE W rather than relying on the default extension i e MOVE means MOVE W POINTER ARITHMETIC PROBLEMS The second possible error is more subtle Suppose you write long int ReturnTimerValues void which accesses a 32 bit hardware register corresponding to the 16 bit Flash and Darken timer register values Look back at the assembler code and also the code generated from the compiled C comments in Listing 5 Both code fragments would correctly execute despite hidden errors Now examine Listing 6 The as sembly code will work but if the program is upgraded to use the supplied C comments the code won t work To access a 32 bit register offset from a hardware base address by 8 bytes use pt SET AO rtnvalue SET DO FLASH EQU 0x08 MOVEA L BASEADDR pt MOVE L FLASH pt rtnvalue But to write the same code in C the correct sequence is not register long int pt register long int rtnvalue define FLASH 0x08 pt long int BASEADDR pt pt FLASH rtnvalue pt The correct sequence must consider the standard relationship in C between pointer value changes and the type of C variable being pointed to The constant Flash must be d
53. able files and lets CF1 programs read and write files on CF cards using the standard DOS Windows media format CF1 programs are written in ANSI C and C using Metrowerks CodeWarrior Professional compiler running under Win95 98 NT or Mac OS PicoDOS provides a 250 firmware function library and API featuring driver support for all of the standard C C library functions and C language interfaces to the 68338 s many integrated peripherals Persistor CF1 costs 395 or 295in OEM quantities Persistor Instruments Inc 508 563 7192 Fax 508 563 7191 www persistor com PERSISTOR Poraistar CFI Users Monwol C C Tonks 16 BIT DATALOGGING STORAGE SCOPE The ADC 216 virtual digital scope combines the functions of a 300 kilosamples s dual channel digital oscilloscope and 150 kHz spectrum analyzer in a PC based virtual instrument that connects to a computer s parallel port Its 16 bit resolution is suited to precision applications like calibration audio development and test and vibration analysis The supplied PicoScope software can operate simul taneously as an oscilloscope spectrum analyzer mul timeter and datalogger Features include onscreen help pull down menus and the ability to overlay a live trace with a stored reference trace Powerful trig gering modes help to capture intermittent or unusual events Save On T rigger saves every trigger event to disk complete with date and time stamp It s easy to
54. akes sense for it to be placed in a volatile register for faster operation Listing 5 illustrates int IsLightOn void which returns a 1 in register DO if the GLOB device rapid flash lamp is turned on The routine checks whether the Lampon bit is set in the GLOB device s control register bit 9 Some compilers return a pointer value in a volatile address register and a data value in a volatile data register The SDS compiler returns both in the volatile data register DO These two approaches lead to different speed advantages Long variables or complex numbers 64 bit may be returned using two volatile registers Structures are returned by moving the return address down the stack and beneath the structure The calling routine programmer must then pull the structure from the stack and make any necessary stack pointer adjustments Even the simple code for int Is LightOn has two possible errors One is in the size definition of a vari able of type int With a 16 bit variant of the 68k processor and an algorithm using only small numbers there s a speed advan tage for using 16 bit integer operations 36 Issue 101 December 1998 On 32 bit processors there s no speed disadvantage for using 32 bit integer operations capable of handling large values without possible overflow Which type of int 16 or 32 bit is intended for int IsLightOn Most C compilers accept either caus ing more code compatibility problems
55. ame but different number of parameters The concept is straightforward but causes problems when you link an object file generated from a C sub routine with custom assembly code Mixing and matching C and assem bler enables you to generate a lot of code quickly but still customize the necessary portions Knowing C coding conventions also provides a useful framework for creating fast easily maintainable code for your assembly language programs l Mike Smith is an instructor in the department of electrical and com puter engineering at the U niversity of Calgary in Canada where he teaches about embedded systems and does research into high speed hardware and software applications in telecommu nications and bioengineering You may reach him at smithGenel ucalgary ca SOURCES SDS Compiler Software Development Systems 800 448 7733 630 971 5900 Fax 630 971 5901 www sdsi com contact contact htm x86 Compiler Inprise Corp 800 457 9527 408 431 1000 www inprise com Issue 101 December 1998 41 FEATURE ARTICLE Ed Thompson Smart Battery Systems 42 According to Ed the Smart Battery System is a remarkable com bination of battery and embedded micro controller technology By giving status feedback on power related issues it s sure to bring many improvements to portable equipment Issue 101 December 1998 linding red lights That s all saw as my car slowed
56. ameters stays constant relative to the frame pointer regardless of how Listing 9 The upper and lower x86 code sequences were generated from the same C code Listing 1 The upper code is produced by invoking a C compiler translation and the lower code is obtained from a C translation Inprise TEXT assume cs _TEXT _main proc near push bp mov bp sp call near ptr _CallAsm pop bp ret _main _TEXT endp ends _TEXT assume cs _TEXT _main proc near push bp mov bp sp call near ptr CallAsm qv pop bp ret _main endp _TEXT ends void Asm void void main void CallAsm void Asm void void main void CallAsm Circuit Cellar INK much the stack is adjusted But there are speed and stack disadvantages too Some compilers solve these problems with a virtual frame pointer thereby generating some interesting code Listing 9 shows some complications of linking between C and assembler The upper assembl y language sequence is generated by placing Listing 1 into main c before activating the Borland now Inprise x86 compiler The gener ated subroutine name _Cal1Asm starts with the anticipated underscore The lower assembl y language se quence is produced from the same code using the same compiler but the code is placed into main cpp The function name is now CallAsm qv Such name mangling means that in C it s possible to distinguish between functions with the same n
57. and are wonder ing where all these funny register names come from they re defined in an in clude file that Microchip provides The PIC16C73 multiplexes different tasks onto a single pin So it s necessary to set certain bits to define the actions of a particular pin Also since the PIC16C73 uses a USART and not a UART you must tell the PIC if the communications sequence will be asynchronous or synchronous Next you need to set up the I O port pins InitPortAB executes this func tion For the purposes of this application both ports A and B are defined as outputs To complete this process a byte of zeros is written to the corresponding TRIS ports All I O ports can be defined as input or output In input mode the port pins are high impedance The PIC16C73 provides a third O port port C Listing 5 maps out the pin definitions Note that included an C 62 Listing 6 The 8051 version of EMIT used a serial interrupt The semicolon is all that stops you here InitOptionRegister pagel movlw B 01000100 movwf OPTION_REG pageO return InitInterrupts pagel movlw B 0110000 movwf INTCON movlw B 00110000 smovwf PIEL not yet pageO return InitMyApp movlw 0 PORTA F PORTB F movwf movwf return interface for future use There s no doubt that it will provide an interface to a Microchip EEPROM device For the PIC challenged out there Listing 5 is a good example of how to define input a
58. and practical problems with this article The starting premise is fine and might be paraphrased if asignal frequency appears to shift significantly with a change in sample rate at least one set of samples was aliased Information theory dictates that a pint pot only contains a pint N yquist s theorem stands because the effect of multiple sample frequencies is to form a higher sample rate In Figure 5 p 32 the proposed multiplexed input and single ADC version requires a very fast ADC This is because some samples occur 1 fsa 1 fsb seconds apart or less where fs is the sample rate and a and b are sample paths With only one ADC some samples coincide so one path must be dominant introducing periodic noise if the paths are not very well matched The width of the spectral lines produced by FFT or DFT depends mainly on the sample rate and sample size Most or all of the center frequencies of two sets of spectral lines won t line up if the sample rates differ The method described adds the amplitudes at these unlike frequencies a bit like adding apples to bananas The analysis method is a version of the Vernier scale which is over 100 years old The Z diagram is just an incarnation of f 2fs f 2fs f 4fs f and on i e 2nfs f known as frequency foldback and is used daily in the aoe 41 0 rotating machinery industry on pumps gas turbines and such hope these aren t considered novel The parting shot hints a
59. anguage UML The UML extensions are from Artisian Software Tools Real Time Studio a tool designed to enable collaborative system development UNIFIED MODELING LANGUAGE A result of the Object Management Group OMG and the efforts of many methodologists UML has become the most widespread notational scheme for system modeling It has made General Custom Options Memory 10 Device Type com x Port Addr 0 3E8 IRQ fa Interrupt Level rep object oriented modeling possible on a wide scale by standardizing a common language that spans multiple organiza tions and modeling tools With UML engineers can define a system level design regardless of many details However when used for real time modeling UML doesn t completely represent the design T here s a lack of direct support for timing considerations hardware support and concurrency or multiple executing threads These fundamental characteristics of real time systems must be addressed if UML is useful to all of the engineering teams ASYNCHRONOUS MODEM Because of its widespread use and familiarity chose a modem for this system design project A typical modem consists of single or multiple processors Power z switch Terminal Application Figure 2 A System Scope diagram shows the external interfaces to the system surrounding the control entities like the system software for the AT command processor and the DSP board along with a number
60. as a Linux file system and populate it with device entries the shell bin sh and a test program In this case used hel 1o which is just a standard Hello World program fea tured in most C books Also placed a startup file profile which instructs the shell to execute my program Once everything is loaded unmount and unmap the file and compress it into a compressed RAM disk image using the program gzip This program is also used to compress the Linux kernel image O nce you have a compressed RAM disk image simply copy this to the boot device along with the kernelimage the autoexec bat file and the loadlin exe utility Voila Figure 1 shows what you need ona simple DO S based bootdisk that will work from flash memory Listing 3 shows the autoexec bat file for this setup The only difference is that decided to use vmlinuz instead of zImage for the ker nel image The name change is purely cosmetic Earlier mentioned that when the Linux kernel boots up it looks for a pro gram in either linuxrc or sbin init If the root device specified as a COMPACTFLASH ADAPTER Samisk 2 Pe Hee Shae Photo 2 These flash based disk modules are used in many digital cameras Adapters for PCMCIA and PC 104 also existfor SanDisk modules 58 Listing 3 This sample autoexec bat file can be used to bootLinux from a DOS file system Often commands to initialize and configure hardware in the system can be use
61. as excellent quality control and my Stamp has shown no signs of misbehavior As we mentioned swapping banks of external code and data space is an alternative to interpreting tokens This method was not truly viable until the advent of the 5 V flash memory Its implementation is conceptually simple but somewhat more difficult to realize The steps to completely repro gramming a system using the bank swap method go in this order The microprocessor wakes up and starts executing out of flash bank A code memory When it s time to repro gram the controller writes new code into flash bank B data memory The microcontroller then executes an instruction common to both old and new code which swaps banks A and B Now bank A is data memory and bank B is code The controller then copies bank B to bank A When the rewrite is complete the controller may starve the watchdog or perform some self reset thereby wak ing up again to execute code out of the newly rewritten bank A Although cumbersome the advan tage of this method is apparent Instead of decoding tokens your micro is free to execute native opcodes Rather than using a special compiler to generate the tokens you can use an off the shelf compiler or assembler for the target Unfortunately this approach may cost your design an extra 15 for the flash memory and glue logic involved Though both solutions work neither is optimal Executing tokens is too slow for many
62. ata M ate T ony Webby Eclipsing Sun Visor Robert E Johnson Missing the Circuit Cellar BBS Then don t forget to join the Circuit Cellar INK newsgroups The cci newsserver is the engineer s place to be on line for questions and advice on embedded control announcements about the magazine or to let us know your thoughts about INK Just visit our home page for directions to become part of the newsgroup experience www circuitcellar com INK ee ait Circuit Cellar INK Issue 101 December 1998 13 FEATURES 1 4 In System Programming YAN A Minimalist Multitasking Executive 26 Object Oriented Design of Real Time Systems 32 Some Assembly Required 42 Smart Battery Systems 14 Issue 101 December 1998 Circuit Cellar INK In System Programming IS people got it made don t they Instant reprogrammability means you don t have to sweat the details Craig and Bill show how system engineers can have that luxury too with an in system program mable target platform FEATURE ARTICLE Craig Pataky amp Bill Maggs Rewriting the Book ny experienced software engineer can relate to the knots in the stomach feeling when a new EPROM is released to production Sure it s time to celebrate but it s also the time to review the wish woulda s and things forgot All your mistakes are about to be duplicated in every one of a thousand units coming off the line
63. atapplications and still have them fit in a flash disk of 1 2 MB Although my example didn tuse any of these its possible to use kernel level modules and dynamic libraries in embed ded applications and run them from the RAM disk W hether or not you want to depends onyour application Forthe smallestapps you ll probably end up building a custom kernel that has only the minimum of what you need statically built in Also your application will be statically linked If CIRCUIT CELLAR INK DECEMBER 1998 root dev ram rw initrd initrd you re using a conventional disk you can think about reducing the run time memory requirements by possibly using dynami cally loaded libraries or kernel modules TAKING OFF In this article I ve shown you that although Linux is traditionally a desktop and server OS with many bells and whistles it s entirely possible to build tiny embedded applications using Linux The examples gave here are all possible with the RedHat distribution which includes both the Lilo and loadlin loader In fact you can boot Linux right off their CDROM using loadlin Linux has the advantages of being almost freely available and familiar to quite a few people also included some resources of where to find Linux support Of course only you can decide if Linux is suitable for your applications RPCEPC Ingo Cyliax has been writing for INK for two years on topics such as embedded systems FPGA design and ro
64. atements made by me above are correct and complete Susan Skolnick Associate Publisher 6 Issue 101 December 1998 Circuit Cellar INK NTA 10 1 1e E NEWS DSP BASED MOTOR CONTROLLER The ADMC331 is a DSP based motor controller featuring power factor correction control capabilities It provides a 26 M IPS 16 bit fixed point DSP core integrated with a 10 bit ADC and peripherals for con trolling AC induction synchronous permanent magnet brushless DC and switched reluctance motors The power factor control peripherals eliminate the need for discrete or IC based active power factor control of the power supply The ADMC331 includes a user programmable three phase 16 bit center based PWM gen eration unit to produce high accuracy PWM signals with minimal software overhead Its seven channel 10 bit ADC is synchronized to the PWM switching frequency and can provide 12 bits of resolution at lower switching frequencies of 6 kHz Power factor correction is enabled by a programmable auxiliary PWM circuit enabling control of frequency duty cycle and phase shift on two dedicated OPEN SOURCE OPERATING SYSTEM Cygnus Solutions has announced eCos a full featured run time solution that is under open source licensing terms This highly configurable application specific operating system is targeted at embedded systems devel ch pae pe Es k gree CYGNUS t ecos eee Documentation Plini Tiria Edited by Harv We
65. ates some output LCD pulses sent to drive motors etc One simple and crude method of going through this process is to have a control loop as the main function loop ing through all the things needing to be done Listing 1 shows you an example The problem is that often you don t want to perform all the steps every time the code goes through the loop Also each subroutine must tempo rarily return to the control loop after some period of time and be able to resume from where it leaves off the next time it s called While this technique works for some programs it s usually more error prone and harder to use than using a multi tasking executive Listing 2 shows a program with a multitasking executive Listing 2 looks similar to Listing 1 but the program is partitioned into independent tasks The tasks don t need to worry about returning control to a high level function and each task may run for a different amount of time before control transfers to another Circuit Cellar INK task In some executives a task may even stop running altogether and wait on some resource to become available before it is run again Since there s only one CPU in reality only one task is run at atime What a multitasking executive does is to periodically take control of the CPU and allow other tasks to run So how does a multitasking system work In a cooperative multitasking system each task voluntarily yields control to the syste
66. botics He is a research engineer at Derivation Sys tems Inc a San Diego based formal synthesis company where he works on formal method design tools for high assur ance systems and develops embedded sys temproducts Before joining DSI Ingo worked for over 12 years as a system and re search engineer for several universities and as an independent consultant You may reach him at cyliax derivation com REFERENCES comp arch embedded comp os linux Linux information www linux org www linuxhg com RedHat www redhat com SOURCE Flash based disk module SanDisk 408 542 0500 Fax 408 5420503 www sandisk com Applied PCs Fred Eady em Ware lop to Bottom Part 9 Launching the Application As Fred journeys into the final frontier he launches a PIC into Internet space using a PCM 4862 Its mission to control tasks according to command s received via the web Can this PIC boldly go where no PIC has gone before f s a professional writer hardware guy and parttime system hacker spend my time thinking about what s out there and what s to come More often than not get firsthand slaps from present and past technology These love taps land either on the butt or in the face depending on my ability to understand and adjust to the language of the technology It doesn t matter if I m working on state of the art gear or really old flighttested hardware For instance the Internet is here and has been for a l
67. ck DataHB Byte Command Slave Address Command Code Ack Slave Address Data Nack stoP Word Command Slave Address Command Code Ack Slave Address DataLB Ack DataHB Nack stoP Call Command Slave Address Command Code Ack DataLB Ack DataHB Slave Address DataLB Ack DataHB Nack stoP Write Command Slave Address Cmd Code Ack Byte Count Ack Data Ac Data Ack Read Command Slave Address Command Code Ack Slave Address Byte Count Ack Data Figure 3 Standard SMBus command protocols provide rules for communicating across the bus and are available to all SBS devices Circuit Cellar INK Issue 101 December 1998 45 SMART BATTERY CHARGER The charger provides a source of voltage and current and communicates with the smart battery over the SM Bus The charger can become a bus master and actively poll the battery for current and voltage requirements A passive charger can act as a slave only device and receive charging in formation from the battery or system host if the battery is unable to provide this information directly The charger may also receive notification of critical battery events e g overcharging over voltage over temperature conditions With S
68. ck size for a task If your task function invokes other functions or uses local variables you should allocate a bigger stack MEMORY MANAGEMENT exec needs to allocate memory to hold the task control blocks and the tasks stacks This allocation can be done by using the C library function memory management routines malloc and free or by using statically allocated global arrays Since exec is meant to be used in a small system the overhead of and possible fragmentation of the memory space by using malloc and free are of concern So we use a simple array allocator instead However you can easily modify the system to use malloc and free Task stacks are supplied as an argu ment to UEXC_CreateTask You should define statically allocated arrays and supply them to UEXC_CreateTask static unsigned char task_stackLUEXC_MIN_STACK_SIZE All the task control blocks are allocated from a global array static TaskControlBlock free_listLNUM_TASKS free_list_ptr A task control block is allocated from the free_list_ptr every timea 24 Issue 101 December 1998 task is created UEXC_Createtask fails if no more task control blocks are available The system initializes free_list_ ptr with the elements in free_list so you can adjust the total number of task control blocks by changing the value of NUM_TASKS When a task is killed or when a task function returns its task control block is released back to the free_list_ptr p
69. cks field int UEXC_StartScheduler void is the code that starts the multitasking scheduler It should be called in your main routine after it creates some tasks This function never returns to the caller and control transfers to the created tasks unless no task was cre ated prior to this call being made It starts the timer interrupt and then calls the internal function Schedule to transfer control to a task Finally void UEXC_Interrupt Driver void is not actually a function but a pointer to a function If nonnull it should contain the address of a function you wish to call at each timer interrupt ASSEMBLY FUNCTIONS These functions need to be modified when porting exec or if you choose to use a different timer counter instead of TOC4 Timer Output Compare 4 under HC11 They don t take any arguments or return any value which should make them easy to port In total there are less than 50 assembly source lines 10 of which deal with the timer registers and can actually be written in C UEXC_SystemInterrupt is the timer interrupt handler After storing the stack pointer to the global variable uexc_current_sp it calls a function to see if the current task s timeslice has run out If it has then a new task is sched uled and control transfers to the new task If the timeslice has not run out handler returns via ReturnFrom Interrupt You must arrange for this handler to be invoked for the appropriate tim
70. classified as volatile or nonvolatile If your project requires little repeated use of variables then designate most of the processor registers as freely available If a later project has different characteristics change the register use convention to optimize that code The trouble with such a general approach is code maintainability A totally arbitrary approach can cause problems if you want to reuse code segments later on It s better to choose a convenient but arbitrary register classification and stick with it If one team member is going to be the C or C compiler the compiler should probably dictate the arbitrary register convention Even if you plan to code only in assembler you still have to adopt some register use approach always recommend adopting a C compatible register convention that balances between making available the maximum number of volatile registers and saving frequently used variables from registers into external memory each time you call a subroutine but lack sufficient nonvolatile registers Listing 3 The asm s code demonstrates how to call both assembly language and C code routines from assembly code Note that there is already one possible source of error present in the code IMPORT _ShowTitle EXPORT _CallAsm CallAsm Provide two entry points to each assembly code function _CallAsm CallAsm JSR ResetDevice JSR _ShowTitle RTS C callable entry point Natural assembler
71. d before loadin exe rem DOS Autoexec boot file for launching Linux with ramdisk rem Author Ingo Cyliax Derivation Systems Inc rem Date Aug 29 1998 rem insert DOS command here needed in order to bring machine rem into sane state rem start Linux loadlin exe vmlinuz boot option is equal to the RAM disk as in my example the kernel uses sbin init But if the root device is different than dev ram and you are specifying a RAM disk with initrd the Linux kernel looks for and executes 1inuxrc If this program exits the kernel unmounts the RAM disk and mounts whatever root de vice has been specified If Linux can t find sbin init or linuxrc it executes bin sh in the hopes that some intelli gent operator will tell it what to do next You might wonder about this strange behavior The reason so root partitions can be mounted from devices not loaded into the kernel Booting from the network is one ex ample of such behavior 1inuxrc can then be a shell script that initializes the network allowing the kernel to mount the required root volume from the network In my case Linux ends up executing bin sh which invokes its startup script in profile but it s always good to know that other options exist Even though created a 1 MB RAM disk image I m only using about 25 of the file system for this example Also the boot disk builtuses less than 700 KB So it should be possible to build some pretty ne
72. directed prefetching illustrated in Figure 2 has become de rigueur The idea is to give the cache a head start with the goal in a perfect world being the elimination of the dreaded miss The conditional branch has become the bane of heavily pipelined super scalar and speculative superdupers Mere mortal CPUs can only take five and wait for new marching orders i e condition resolves The latest chips go to extraordinary lengths trying to predict the branch s outcome For instance the DEC now Compaq Alpha 21264 happily wades 20 branches into the future relying on a crystal ball that not only includes the usual branch history but also how the program arrived there See Figure 3 IN MEMORY OF CRAY Another example of effective recy cling of yesterday s know how is seen in the widespread adoption of SIMD techniques i e applying a single instruction to multiple data items in parallel In Cray s day this technique was known as vector processing Dual FP multiply accumulate units Dual FP divide SQRT units Ly Rename p registers execution units fed the cache Figure 1 With plenty of function units out of order execution high clock rate and huge 0 5 MB instruction 1 MB data caches the HP PA 8500 is a good example of the latest trend for performance at any price chips Dual load store address adders Retire Rename registers Architected
73. don t care Here the micro ae s put it there outputs zz 01 OC 12 12 is the data i EMP value to enable timerO interrupts Not only can rogram the flash t sput it there OSAN CAN yOu POT a Ea i E value for global interrupt enable code space but also the EEPROM t TE put it there nonvolatile data space Some devices have prel i which j f loop forever a epre paded ey CEOS s R l F handles decrementing the registers for count_high let you determine vendor code part count_low times family flash size and part number as ister Variables long as the device isn t protected def CNTL rl6 def r17 Parts can be protected two ways f H r18 First the device can be write protected def RL r19 so no further code can be programmed def iA H Second it can be locked so the code RY 0 i continue can no longer be written to or read 4 from the micro 76 Issue 101 December 1998 Circuit Cellar INK GROUNDED As wonderful as the AVR is there s room for improvement found some errors in the command words listed in the AVR9Q10 In System Programming App Note Although the information given in the datasheet was correct it took a few hours of head scratching to get all the commands working correctly The micro doesn t give feedback on the status of a programming cycle You have to wait 4 ms between writes to the device It seems to me that the MISO bit could have been held high until the programming c
74. dressing using one of three possible 16 bit pointers Each can load or store with automatic pre decrementing or postincrementing of the pointer The bit instructions are similar to the branch instructions in that there are separate instructions for setting and clearing every status flag There are a few areas where com mands aren t obvious All the status timer interrupt and ports control registers are considered I O ports and have few commands Values can be moved to or from them using only the 32 RAM register files To movea constant to a port it must go through a RAM register first Moving data between any of the RAM registers is straightforward keeping in mind that you can only load a constant into RAM registers 16 32 Once you see the advantages of programming the AVR line in a 16 bit address space dealing with 118 com mands isn t so scary But that s why programmers get the big bucks To use a micro efficiently Circuit Cellar INK they spend a lot of time getting familiar and comfortable with it You know picking a microcontroller is like picking out a shirt They come in many styles patterns and colors but they all do the same job You just find one that feels and looks good to you recommend the AVR It s pretty darn comfortable i Jeff Bachiochi pronounced BAH key AH key is an electrical engineer on Circuit Cellar INK s engineering staff His background includes pr
75. e fined as 0x08 sizeof long int and not by the offset defined in T able 3 register long int pt register long int rtnvalue define FLASH 2 pt long int BASEADDR pt pt FLASH rtnvalue pt Pointer arithmetic in assembly code is based around byte arithmetic so the Timer registers are offset by 8 bytes from the hardware base address But pointer arithmetic in C is based on the type of variable being pointed to Thus if offset 1 incrementing a pointer by an amount offset in C changes the pointer value by 1 char by 2 short int by 4 long int or maybe by a strange amount struct mystruct Considering how C handles pointers there must be two register offset definition files one for C and one for assembly code Listing 4 There are many approaches to avoid destroying register values within a subroutine An abso lute addressing mode is used within ResetDeviceV2 The register is saved and later recovered from the stack during ResetDeviceV3 ResetDeviceV2 OVE L RESET RTS ResetDeviceV3 OVE L AO SP SET OVEA L BASEADDR pt OVE L RESET CONTROL pt OVE L SP AO Circuit Cellar INK Epilogue Uses absolute addressing mode BASEADDR CONTROL Save and recover register value Prologue Listing 5 used the offset to the con trol register 0 By chance this is the same measured in bytes short int or long int However th
76. e A standard J1 P1 stack through connector enables the IOCP 74 to reside anywhere within an 8 bit PC 104 stack Adding an optional J2 P2 connector provides 16 bitstack through compatibility and access to all upper interrupt request lines The 10 CP 74 sells for 185 Scidyne 781 293 3059 Fax 781 293 4034 www scidyne com Annasoft Systems 619 674 6155 Fax 619 673 1432 www annasoft com Process Boundary Interface Stub COM Server COM Library Interface Machine Boundary Interface Server Stub CON Selver Nouveau PU 50 CIRCUIT CELLAR INK DECEMBER 1998 SVGA ADAPTER FOR PC 104 The VGA 104 SVGA adapter for PC 104 applications is based on the 65545 VGA controller from Chips and Technologies It supports up to 1 MB of video resulting in memory resolutons from 640 x 480 x 16 million colorsto 1280 x 1024 x16 and hashardware window acceleration It can drive active matrix and dualscan LCD EL and plasma flat panel displays as well as CRT monitors The VGA 104 provides PC 104 systems with an industry standard display interface supported by both desktop and embedded operating systems The VG A 104 provides supportfor 3 3 and 5 V flatpanels and has power sequencing logic for LCD and backlight voltages A large library of flatpanel support packages is available Each package includes panel specific VGA BIOS cabling and technical references The VGA 104 is available for 155 in 100 piece quantities
77. e 1 C language constructs were originally designed to take advantage of the processor s instruction set Allocate registers based on frequency Perform branch optimization Put frequent constants in registers Called functions cleanup Dead code elimination Local common subexpression elimination Allow inline functions C only L Perform lifetime analysis R Enable automatic register allocation S Optimize for size vs optimize for speed T Volatile variables must be declared volatile U Remove unreachable code Y Enable aggressive switch algorithms Table 2 Optimizations such as these from the SDS CC68000 compiler provide the programmer with a wide range of register and memory usage optimazations always apparent and are often insignifi cant in terms of increased program speed If you spend an hour shaving 1 ms from some code that code block must be run 3 6 million times before there s a payback With today s faster processors you probably saved 0 01 ms One important and difficult thing to come to terms with is sharing There s one set of processor and system resources Sharing must occur whether a team uses common assembl y lan guage subroutines or one programmer switches between C C and assembler EXHIBIT A In the November 15 1997 issue of New Scientist read about some interesting crime detection hardware that provides a good example of how to link C and assembly code Apparently it s diffic
78. e Bill as give his latest bloatware the three finger salute But there s no doubt his mach inations have enabled standardization arguably a good thing And obtaining a monopolistic position isn t illegal It s the way it s obtained and whether it s abused that deserves scrutiny Ultimately my ambivalence is a reflection of a somewhat libertarian bent As they say about democracy we 84 Issue 101 December 1998 Circuit Cellar INK get the government we deserve The same goes for free enterprise and that means we get the OS we deserve too HOT CHIPS FOREVER All in all Hot Chips X was a rousing success Each year worry whether the chips will be hot enough to keep the conference going and invariably come away revitalized knowing that silicon has still got legs As the conference moves into a second decade extend my apprecia tion to the organizers Summer in the Silicon Valley just wouldn t be the same without their efforts I d also like to call your attention to anew cousin Hot Interconnects Judging by the program the confer ence covers some interesting topics such as What s wrong with cable technology Grand challenges of the internet and the intriguingly titled What love to hate As we move into an era when com municating is just as important as com puting figure Hot Interconnects will join Hot Chips on my calendar kl Tom Cantrell has been worki
79. e and that they should place their orders with company B Then he swiped copies of company A s customer data and gave it to com pany B To top it off he erased all the records on company A s computers as he headed out the door You don t need to be a legal giant to deal with this case Until now perhaps the most obnox ious byproduct of trade secret law was the zillion page nondisclosure agree ments that we ve all signed and per haps even read But a number of intriguing cases have surfaced involv ing the trade secrets you carry around in your head The way the wind is blowing with noncompete clauses and the like alobotomy may become a standard part of the exit interview Shakespeare wrote The first thing we do let s kill all the lawyers King Henry VI Part Il Act 4 Scene 2 but like to think he would have spared Ms Radin who had this final bit of good hearted advice Stay away from a lawyer who claims the answer is clear BILL BASHING The evening discussion panel ar ranged by impresario John Wharton is always good fun This year s topic was Confronting the Microsoft challenge In other words can and or should Microsoft be stopped Wharton related some of the diffi culties in getting a panel together Many would be panelists sealed their fate with responses like After each panelist stands up and says No Microsoft can t be stopped how do you plan to kill the other 85 mi
80. e assembly code to handle some special algorithmic match with an unusual processor feature SDS recom mends that hardware register access be performed from assembly language in all but the simplest situations Either way you need to mix and match between subroutines that were quickly made functional via C and those hand written highly customized assembly language sequences In this article introduce the key elements of the skill of mixing and matching THINGS TO PONDER Linking between C and assembly code isn t so difficult if you ll accept a few basic facts For one there s nothing magic about code generated by a C C compiler It uses the same instructions and system resources as the assembly language programmer There are a number of ways to per form any given operation One ap proach may take advantage of a certain processor feature whereas another takes advantage of a different feature When linking between C and assem bly code the relative advantages aren t The most obvious C construct Motorola processor Intel processor SDS compiler Inprise compiler shown in Table 1 is to value ADDQ L 1 D3 Fast INC si Fast use the operator in a loop value rather than a slower arithmetic value value CONST ADD L CONST D3 Slow MOVE ax si ADD ax CONST Slow MOVE si ax addition value value CONST Other Circuit Cellar INK Tabl
81. e offset to the Timer registers for Listing 6 was eight bytes but only two long ints That s one reason to recommend that hardware register access be handled in assembly code But with many hardware registers on real devices remaining 8 bits wide much C code is written without people being aware of the problems of upgrading hardware to a 16 bit version PASSING PARAMETERS A common requirement is the ability to pass parameters between C and assembl y code routines You may want to pass a pointer and data value to control two identical devices placed at different base addresses on a proces sor bus Also parameters can be passed on the memory stack in registers especially with windowed processors like SPARC or using a combination Originally subroutines were used to avoid repeating coded sections Now they abstract the ideas to make code more maintainable ensuring that no code contains more than 7 2 ideas Many compilers can analyze code to determine whether a call can be optimized by replacement with in line code Often when a call is made to short subroutines the subroutine code may be physically placed many times within the main code and the final code to be placed in ROM may still be shorter than the code needed to pass parameters the standard way In newer language extensions the high level language programmer can specify that a subroutine be handled this way see Table 3 This automated approach achieves code ma
82. eam at work they ll know that their lifesaving equipment has the power to handle the job i Ed Thompson is president of Micro Computer Control Corp For the last six years he has concentrated on C bus applications and development tools You may reach him at 73062 3336 compuserve com REFERENCE 1 Smart Battery System Forum System Management Bus Speci fication www sbs forum org RESOURCES Micro Computer Control The I C Bus and How to Use lt www mcc us com i2chowto htm D Stolitzka Smart battery tech nologies push design Electronic Engineering Times January 27 66 84 1997 www techweb com se directlink cgi EET 19970127S0095 Table 2 Smart battery data describes the actual and predicted operation of an SBS smart battery By being located within the battery itself this information is accurate even if the battery is changed 46 Issue 101 December 1998 Circuit Cellar INK 48 53 59 Nouveau PC edited by Harv Weiner Real Time PC Embedded RT Linux Part 2 W orking with Flash M emory Ingo Cyliax Er Applied PCs emWare Top to Bottom Part2 Launching the Application aE Fred Eady FLASHTCP SERVER The FlashTCP Server provides a low cost platform for embedded systems requiring Internet or network connectivity Its preinstalled TC P IP stack and DOS file system make the unitideal for applications needing TCP IP connectivity Server applications i
83. edited by Harv Weiner 53 RPC Real Time PC Embedded RT Linux Part 2 Working with Flash Memory Ingo Cyliax Applied PCs emWare T op to Bottom Part 2 Launching the Application Fred Eady ss 59 ave Task Manager Elizabeth Laurencot The Word is Communication Reader I O New Product News edited by Harv Weiner INK On line Advertiser s Index January Preview Priority Interrupt Steve Ciarcia Embedded Happenings Ss 2 LE 95 96 Circuit Cellar INK Issue 101 December 1998 3 S Gerard Fonte s recent article Breaking Nyquist INK 99 evoked more than just a few casual responses from INK readers Here s a bit of I O on the topic What Gerard doesn t seem to understand is that if you re sampling a signal at 10 kHz and also at 9 kHz you re effectively sampling at 19 kHz not 10 kHz The theoretical Nyquist limit is 9 5 kHz and there s no chance to detect arbitrary signals above this point Using this method becomes unnecessarily complex when you can sample at 20 kHz in the first place Since the premise is that 10 kHz is the highest rate the output of two alternating 10 kHz ADCs would be fed into the DSP That s the same as a conventional system running at 20 kHz Darrell Hambley dth red primextech com hope you ve been deluged with mail about Breaking Nyquist have 16 years of experience with the use and abuse of aliasing and see major theoretical
84. er interrupt In most cases this means putting the address of this function in the interrupt vector table If you are using a debug monitor typically the monitor provides a RAM based pseudo vector table The function UEXC_SavregsAnd Resched is called by UEXC_Defer to create a fake interrupt stack UEXC_StartNewTask is called to run anew task The stack is set up so that if the task function ever returns then an internal function UEXC_Ki11 Self is called UEXC_Ki11Self is equivalent to UEXC_Kil1lTask current_task gt tid The UEXC_Resume is a function that gets the stack pointer from uexc_ current_sp and does a ReturnFrom Interrupt The function UEXC_StartTimer can be written in C but we put it in the set of assembler functions because it is microcontroller specific It needs to set the timer registers to enable the timer interrupt at INTERRUPT_CYCLES later TOC4 is used in the supplied code Typically a TOC function can be associated with an output pin but in this case the output pin function is disabled The value given by INTERRUPT_ CYCLES is the system tick and must be adjusted for different system clock speeds As supplied it is defined to be 2000 cycles UEXC_RestartTimer can also be written in C It simply reenables the timer interrupt at INTERRUPT_CYCLES later GIVE IT A TRY The simple example shown in Listing 4 creates two tasks that print out Os and 1s In addition to traditional programming
85. erates code that runs faster than the original Reset Device During ResetDeviceV3 the original address register value is saved to the processor stack PROLOGUE and the register used and the old value is recovered from the stack EPI LOGUE The first approach is inconvenient and doesn t provide easily maintainable code if many adjacent hardware regis ter locations must be accessed T he second option looks like overkill the address register AQ doesn t store anything useful during eight subroutines out of ten But whenever the register stores some critical value your pro gram is heading for never never land The problem is the need to save all possibly important registers on entry to each subroutine You never know whether other team members used that address register This situation leads to slow code whether it s writ ten in C or assembler One solution is to identify two register classes Volatile or temporary registers are those that everyone agrees will not hold useful values They can be used in a subroutine without having to be saved to slow external memory N onvolatile registers must be saved and later recovered if they re used in a subroutine mention registers here because placing frequently used vari ables into registers is often the route to fast code On processor register to register operations are significantly faster than external memory accesses Everyone must agree which registers are
86. es and twenty 1000 second prizes Details concerning both the contest and the GP20 are posted at www circuitcellar com But that presentation was also exciting for me because had the opportunity to talk about the incredible year Circuit Cellar has had In 1998 January marked the tenth anniversary November was the 100 issue and now this a design contest sponsored by the world s largest producer of MCUs Hey is this like Microsoft bundling some small company s software Then again at the show also ran into some PR and marketing types who needed me to explain what you already know Circuit Cellar is an engineering applications magazine for the engineer the end user not the marketing folks Happily even some marketeers found it an exciting even novel approach One director of marketing that met with called Circuit Cellar a sleeper saying that he was tired of obnoxious sales oriented publications He recognized that Circuit Cellar has value Naturally agree Those were the kinds of conversations that started the dialog going Who we are What we re doing What s our goal Who do we serve The most important answer we serve the engineer What good is advertorial that isn t useful to the engineer And who better to know what is useful than engineers themselves right That s why best of all it was so great to meet with the real designers the ones who know about Circuit Cellar who seek us out who don
87. ething different is always refreshing In contrast to ESC W the Embedded Internet Workshop was a flashback to the days of entrepreneurial startups and involved principles Co sponsored by Circuit Cellar and RTC Magazine workshop organizer Lance Leventhal provided a forum where 200 industry enthusiasts met with embedded Internet specialists and a score of emerging companies The discussion was lively and the enthusiasm infectious About the only thing that everyone agreed on was that the Internet is there and is a cheap accessible data pipe Like anything computer these days user commitment ranged from embedded Internet everything fanaticism to show me reserved engagement I d like to think I m slightly left of center know that eventually it will be cost effective to add Internet accessibility to things like industrial controls security systems and vehicles It probably won t even be very long before we have printers that e mail toner paper and error status conditions However can wait for flush monitored toilets and coffee machines that e mail you when the coffee is ready was certainly surprised by the range of options presented by the dozens of workshop exhibitors was familiar with the high end solutions from companies like PharLap and low end micro servers from emWare but was astonished at the advances from some of the new players in the game NETsilicon presented an ARM based Ethernet ready under 30 ASIC aimed primarily at printer manu
88. f BatteryMode CAPACITY_MODE bit 0 else in 10 mWh Theoretical voltage of anew pack in millivolts Smart battery specification version supported voltage and current scaling information Date the cell pack was manufactured Battery serial number Battery s manufacturer s name Battery s name Battery s chemistry Content determined by battery manufacturer Selector configuration data identifies the battery connected to the SM Bus host the current system power source which battery is connected to the charger and what batteries are present This data enables the host to determine when a smart battery has been added or removed if AC power is connected or not and when the selector switches from one battery to another A selector may act as a slave only device responding to polls from the host as a master device initiating com mands to the host or as a combination POWERFUL DEMANDS The SBS is destined to move beyond portable computers and cell phones and into a widening range of portable electronic products It offers extended product runtimes the ability to accu rately predict performance and im proved charging safety Portable medical equipment is one product category that will soon ben efit from SBS technology Others will certainly follow If you re responsible for portable product design and devel opment maybe you should consider this technology too Hopefully the next time you see an emergency t
89. facturers It appeared to be one of the few solutions capable of satisfying both communication and control tasks in one chip Not to be upstaged Vadem was there with their VG330 single chip x86 compatible Based on a NEC V30 core and aimed at handheld organizer and POS terminal manufactures the 160 pin Vadem chip attempts to provide a cost effective transition from traditional embedded PC to more cost sensitive x86 applications In my opinion the most remarkable product entry came from iReady Their product is basically a low cost custom Z 80 core ASIC with all the Internet functions built completely in hardware It was described as so dumb that it s impossible to crash I d rather interpret that as reliable Working together with Seiko to add display electronics they ve produced TCP IP ready LCD displays with built in network e mail and web browsing capability The iReady ASIC is also incorporated in a children s electronic toy scheduled to hit the market in early 99 So what s next The refrigerator Don t be so surprised The subject definitely came up and you can bet your PC that someone will eventually offer it Purists will tout the necessity for intelligent refrigerators that automatically e mail a shopping list to the grocery store and magically restock themselves Somehow think that less spectacular applications like simply knowing the temperature and contents as part of an overall home automation system will invite more
90. ficant energy at two three and four and five six etc times the sample rate To pro duce a clean output a sharp cutoff filter iS needed to suppress these components The waveform in Figure 2a is also high for 47 clocks out of every 64 as shown by the first bin of its FFT in Figure 2b However it only has signifi cant other energy at 16 and 32 times the sample rate which means that a much simpler filter can be used Obviously if the desired output value is 1 or 63 out of a possible 64 there is only one possible waveform in each case 1 high and 63 low or 63 high and 1 low respectively The filter ing requirements of both schemes are identical in these cases Deltasigma modulation goes hand in hand with oversampling i e using a sample clock much higher than the highest frequency in the signal to be digitized Just like with PWM you re trading off resolution in time against resolution in the measurement do main By taking short term averages of the binary waveform you get the analog values you re looking for Figure 3a shows the concept behind a delta sigma modulator The major components are a difference amplifier an integrator indicated by its LaPlace trans form a quantizer with a single decision level a sampling device and a simple two level DAC The quantizer is nothing more than a comparator with a one bit digital output and the sampler is simply a flip flop The DAC is often implemented
91. g InputCircularBuffer OutputCircularBuffer AsyncData_1 O AT Command Processor LastATCommand ReadFromTerminal WriteToTerminal GetNextCommandFromTerminal 1 SendCommandToOtherSubsystems 1 1 1 1 DataManager Configuration i 1 ErrorManager Configuration CorrectData DataControl As the processing capabili ties of embedded systems increase along with their ability to address memory in the gigabyte range the small penalties in processing time and memory usage resulting from OO technology become less significant CompressData 4 1 SignalProcessing 1 DataPumpController StoreDefaultValues ConfigureFilters SendDataOut ReceiveData Figure 8 In a Class diagram all the identified classes are grouped together in packages based on their roles in the system This Class diagram is contained in four different packages which was modeled in UML the instru ment required data ccommunication capabilities through a modem interface The UML notation was used to implement support for a modem and distributed computing in a networked environment This machine is a typical but by no means comprehensive ex ample of an embedded UML project So it seems appropriate to make the bold statement that OO technology and UML are here to stay in the real time industry i Irv Badr is chief systems engi neer at Artisan Software To
92. g occurs Each call is designed to give EMIT time to process any requests it receives No call in 100p3 should wait for any input or output process to provide a status Such a wait can induce a hang condition causing EMIT to miss data and commands it needs to process Now I ve successfully initialized a PIC16C73 to communicate via RS 232 to an Advantech PCM 4862 equipped with EMIT and a web browser By including the emWare PIC code in the source enabled the PIC16C73 to pass data to and receive commands from the EMIT software interface The results are controlled and displayed by a web browser using a GUI that designed with Visual Caf get address to poke put into FSR get the data to poke btfsc FSR 7 check to see what page we want switch page if necessary always return to page0 get address to peek put into FSR put address into packet btfsc FSR 7 check my pages switch page if necessary always return to page0 put data into packet THE PURPOSE ports So you can send a command to The idea here is to open up the read and write a particular register via an PIC16C73 to the programmer The PIC EMIT web browser interface As you saw 16C73 is register based including the O this little application does nothing but set Listing 8 Note that the attributes are ORed for definition NCTIONS Defines
93. gress clock heard a proverb some where about a watched EPROM never erasing so try to make myself get up and stretch Usually this involves a trip to the kitchen It doesn t matter where am if go in the kitchen always open the fridge and stare into it Even if I m not look ing for anything in particular Microchip was the first to give me what was looking for a micro with electrically erasable program memory It s no surprise that it has become my mainstay The F84 enables immediate code changes by skipping the UV cycle So what if it requires a special program ming voltage TAKING WING Atmel the longtime leader in EPROM EEPROM and flash memory finally caught on to what Microchip has known for along time T here s gold in them there flash based micros So Atmel introduced an advanced single voltage flash based microcon troller The AVR enhanced RISC micro controllers offer the highest MIPS per milliwatt capability in the 8 bit MCU market Higher level languages are making their way into an everyday coexistence with small micros And the AVR s hardware and software architecture was developed with special attention to highly efficient C code generation The use of many general purpose registers elimi nates the bottlenecks of 8 Bit data bus having to use an accumu Stack pointer Program counter Internal oscillator lator to move data around Althoug
94. gs that illustrate how various users interact with the system requirements power switch and status LEDs These interfaces surround the control entities e g the system software and DSP subsystem From the operational perspective a system may undergo different modes of operation depending on a set of events that may occur For example the System M ode diagram captures the Failure Calibration and Software Update modes Figure 3 shows a System Mode diagram for my modem with the modes defined as Command Con nected and U pdate Firmware The Command mode is entered when the modem is first powered up and re sponds to the AT commands Once the phone connection is es tablished the modem enters the Con nected mode where data is pumped to the modem on the other side of the connection At this stage the modem bypasses the AT command processor The U pdate Firmware mode is entered once a specified string is en countered during command mode and triggers a change In this mode subse quent data transferred to the modem contains the executable code that updates the version of the modem operating software Object Sequence diagrams OSDs show the interaction between objects and actors through events and opera Command lt _ l Esteblish Connection phone lost connection Update complete Update firmware Connected Figure 3 The System Mode diagram illust
95. h many micros Program flash Watchdog timer SRAM le control Timing and wardly compatible to the larger parts capable of using the full 64 KB space Figure 1 gives you an idea of the 90S2323 architecture Of interest here are the 32 x require a clock division of up to 12 for an execution MCU control register Y Instruction General register purpose cycle the AVR enhanced RISC microcontrollers execute an instruction on every oscillator cycle Prefetching enables most Instruction decoder registers Timer counter Interrupt unit v Control lines yY Status of the 118 instructions to E FERRON be executed in 100 ns with a 10 M Hz crystal Progam ino ia SPI 8 general purpose registers The last six registers can be used as register pairs These pairs called X Y and Z have some special 16 bit addressing functions associ ated with them As well there are 128 additional bytes of internal SRAM stack Atma has a full line of competitive parts in 20 to 64 pin sizes believe Atmel s entry into the marketplace with some 8 pin micros is significant Meanwhile Microchip has been quietly proving the practicality of the 8 pin micro and chuckling about it all the way to the bank The AVR AT 9082323 is the low end 8 pin micro with three general purpose I O pins The si
96. he RMS value The uniform PDF has the lowest peak to RMS ratio while the Gaussian has the highest The triangular PDF falls in between the other two The shape of the frequency spectrum of arandom signal is independent of its PDF Since the linearization and modulation masking properties of the signal are a function of the PDF the spectrum can be chosen or shaped to optimize how the noise relates to the desired signal For example if the signal energy is primarily in lower frequency bands the random signal can be shaped to put more of its energy in upper bands mak ing it easier for the ear to separate them In an audio application you might run the noise through a simple differ entiator by taking the difference be tween successive samples This process gives the noise a rising 6 dB per octave slope you could call this blue noise to distinguish it from pink noise which falls off at 3 dB per octave Figure 6 Adding dither to a fading signal makes a huge difference in how the quantized result is perceived a The undithered system shows harmonic structure changes and noise modulation b The dithered system has less waveform distortion and a constant noise level Circuit Cellar INK Figure 7 Some important probability distribution functions are Gaussian a uniform b and triangular c Each has a total area of one square unit under the curve If the signal was preemphasized before quantizing the high f
97. he average number of copies of each issue during the preceding twelve months are A Total number of copies printed net press run 29 783 B Paid Circulation 1 Sales through dealers and carriers street vendors and counter sales 4 270 2 Mail subscriptions 20 922 C Total paid circulation 25 192 D Free distribution by mail samples complimentary and other free 1 404 E Free distribution outside the mail carrier or other means 160 F Total free distribution 1 564 G Total Distribution 26 756 H Copies not distributed 1 Office use leftover unaccounted spoiled after printing 321 2 Returns from News Agents 2 706 Total 29 783 Percent paid and or requested circulation 94 2 Actual number of copies of the single issue published nearest to filing date are November 1998 Issue 100 A Total number of copies printed net press run 30 200 B Paid Circulation 1 Sales through dealers and carriers street vendors and counter sales 4 647 2 Mail subscriptions 21 767 C Total paid circulation 26 414 D Free distribution by mail samples complimentary and other free 1 050 E Free distribution outside the mail carrier or other means 240 F Total free distribution 1 290 G Total Distribution 27 704 H Copies not distributed 1 Office use leftover unaccounted spoiled after printing 562 2 Returns from News Agents 1 934 I Total 30 200 Percent paid and or requested circulation 95 3 certify that the st
98. heir use is warranted For example under exec we use two global variables to pass information between C and assembly routines The alternative is to use normal argument passing between the routines but that would be compiler and microcontroller dependent making it difficult to port exec using other compilers or to other microcontrollers void uexc_current_func void unsigned char uexc_current_sp uexc_current_func is the pointer to the function for the current task and is needed only to start a new task uexc_current_sp is the current stack pointer or the address of the sp field of the current task The latter is used by UEXC_Defer to tell the assembly routine where to store the stack pointer after the interrupt frame is created exec uses a few other global vari ables and macros such as static TaskControlBlock current_ task This global variable points to the task control block of the current task All the tasks are linked in a cir cular list so the next task to execute is given by current_task gt next void UEXC_InterruptDriver void contains the address of a function to call whenever the timer interrupt triggers If you have more than one function to call you can chain them together The NUM_TASKS macro is the maxi mum number of task control blocks that can be allocated You should change this to match the number of tasks you have in your system The macro UEXC_MIN_STACK_SIZE defines the minimum sta
99. here are two sleep modes Idle mode enables the timer to continue for a wakeup on timer overflow Power down mode can leave the watchdog running to wake up the micro or stop everything and wake up only ona level interrupt or reset A 32 768 Hz clock crystal enables the prescaler and timer to work well together providing a nice overflow time With a 64 prescaler and a 256 timer overflow you get a divide by 16 384 which gives 0 5 s with the 32 768 Hz crystal The initialization routine samples the two configuration inputs and sets up a three byte counter for two 1 s 120 1 min 7200 1 h or 172 800 overflows 1 day At this point the TimerO interrupt pretty much runs the show At each timer overflow a check of the 3 byte counter is performed When it reaches zero the output PB1 is set and the counter is reloaded for the next count down If the count isn t zero the counter decrements and the output PB1 is cleared This way the output only stays high for 0 5 s regardless of what timeout is selected PREPARE FOR TAKEOFF The Atmel AT 90S2323 has 118 instructions This may sound over whelming but they break down into four major groups arithmetic logic branch transfer and bit instructions Most of the arithmetic logic in structions deal with two registers or a register and a constant The majority of the branch instructions are based on status flag states Many transfer instructions deal with indirect ad
100. his by running the kernel configuration script 53 Photos 1a and 1b show screenshots of the graphical interface to this configuration script You sim ply decide which modules you want included in a kernel build and save the configuration For many configuration options and device drivers you can choose to select module support This way you can place the compiled code that implements the option or device driver into a loadable object module that is stored on the disk By putting the driver in modules you can reduce the run time memory require ments of the kernel When you need a certain feature the module is loaded into the kernel space and initialized Once you re done with the feature the module is unloaded and memory is reclaimed The kernel module loader can be used explicitly to load kernel modules via com mands to load unload and list the mod ules currently loaded As well Linux has a dynamic kernel loader which simply loads required modules as soon as the kernel needs them You can use which ever method suits your application The downside of using modules is maintainability Because kernel modules have to be stored on the disk you have to make sure they re on the disk when they are needed And because many modules are needed its often more difficult to track their interdependency and version than if all the modules are statically loaded into a single kernel image O nce you configure the kernel a
101. i cations portion of this application Their names tell the story By the way the __ CONFIG parameter denotes the use of an HS oscillator with no watchdog timer and no code protection Listing 2 is simply a macro declaration Some of the more complex PICs use pages to multiplex register addresses As you Listing 3 Note the inclusion of the two EMIT modules These tie the app fo emWare code ORG 0 Goto loopd org 4 include isr inc loopo call InitMicroController call EmInit CALL InitMyApp bsf INTCON GIE loop3 call call call goto PollSCI MyApplication EmMicroEntry loop3 MyApplication return CIRCUIT CELLAR INK DECEMBER 1998 INTERRUPT_SERVICE_ROUTINE enable interrupts Listing 4 Inifializing ports on the PIC is important because of the complex nature of the 1 0 module InitMicroController call InitUSART call InitPortAB call InitPortc call InitOptionRegister call InitInterrupts call InitMyApp return see in the macro definitions the PIC 6C73 is one of these devices A single bit in the Status register delin eates page O and page 1 When you re programming PICs with pages it can get confusing as to which page you re on and whether you swapped that page bit or not Using a macro cuts down on the confusion factor when things just don t act right in the application The beginning of Listing 3 looks like code for a bunch of other microcontrollers The first line jumps
102. included is a pair of SHARC serial ports and six 40 MB link ports for connecting to link portcompatible devices such as the bitsi 104 mezzanine interface and the other SHARCs The board combines the power and ruggedness needed for embedded systems designed for military or industrial environments and space constrained applications requiring very high floating point com putational performance The Silvertip Quad PC 104 board is also available in a dual processor configuration Source code development tools for the Silvertip Quad PC 104 include Analog Devices SHARC AN Sl compliant C compiler assembler linker simulator and sourcecode debugger True realtime in circuit emulation is available with the optional EZ ICE emulator from Analog Devices BittW are s DSP21k Toolkit provides developers with C callable host I O functions DSP functions example code and diagnostic utilities for 32 bit versions for W indows 95 and Windows NT The DSP21k porting kit is also available to support the Silvertip Quad PC 104 on additional platforms and operating systems Pricing for the Silvertip Quad PC 104 starts at 4595 BittWare Research Systems 603 226 0404 Fax 603 226 6667 www bittware com edited by Harv W einer Nouveau PU 48 CIRCUIT CELLAR INK DECEMBER 1998 PC 104 I O COPROCESSOR MODULE The IOCP 74 is an 8 bitPC 104 compli antmodule thatis designed to perform sophisticated mea surement and control operations with mi
103. ine by line 60 Listing 1 The include statement keeps you from having to remember all those funny register names LIST p 16c73 include lt p16c73 inc gt __ CONFIG B 111010 define crystalFreq define baudRate D 9600 SPBRG_VALUE EQU BitVarl 0 BitVarl 1 define gotChar define txEmpty D 10000000 crystalFreq baudRate D 64 1 Listing 2 It s just as easy to only code these but it s easier to read this way MACRO bef STATUS RPO ENDM pageO MACRO bsf STATUS RPO ENDM Some time ago built a realtime PIC emulator for PIC 6C5 x devices It consisted of lots of latch logic coupled to memory and a proprietary bondout device The design was simple enough but the necessary software was really heavy moved quite a few units and found that most of us like to know what s going on inside the devices we write apps for The application lm about to examine is a simpler version of that old emulator Listing 1 is a code snippet that defines and computes the data rate generator value versus the crystal frequency Note that a crystal frequency of 10 MHz is used to derive a data rate value for 9600 bps This formula is provided in the datasheet for the PIC16C73 You can compute this data rate outside the program and insert it manually but why not use the power of the PIC Macro assembler That s just what did Two bits are also defined in Listing 1 These bits are used in the serial commun
104. iner high frequency PWM outputs These signals are useful in front end switching power factor correction stages Additional on chip peripherals include a 16 bit watchdog timer and 24 bit DIO ports Two flexible doubl ebuffered bidirectional synchronous serial ports enable a variety of communica tion protocols The program memory in cludes 2K x 24 bit RAM and 2K x 24 bit ROM Data mem ory includes 1K x 16 bit RAM Both can be boot loaded through the serial port from a serial ROM EEPROM or UART or synchronous connection As well the ROM motor control functions support an interac tive mode The ADMC331 is available in an 80 pin TQFP package and costs under 5 in large quantities Analog Devices Inc 781 937 1428 Fax 781 821 4273 www analog com motorcontrol opment The complete eCos environment includes all kernel components HAL layers ulTRON configuration C runtime math libraries and drivers The source level configuration more than 170 configuration points means that this OS can exactly match the needs of the application eCos provides an open source infrastructure that enables embedded system developers to focus on differentiating their products rather than the development maintenance or configuration of a real time kernel The addition of eCos to Cygnus s GNUPro environment provides developers with basic components like compilers debuggers and real time kernels Cygnus s eCos is a royalty free OS
105. intainability and the speed of straight line coding Listing 7 shows how an SDS 68k compiler passes parameters to the C routines void PassMany long int outparl short int outpar2 long int outpar3 and void PassOne long int outparl from an assembly language code sequence First a stack frame is established A compiler can keep track of which variables are or are not pushed onto the memory stack 38 Issue 101 December 1998 Listing 5 The function int IsLampOn void demonstrates the use of a volatile register to return a parameter Note that there are two hidden sources of error in this simple function IsLightOn PORT _IsLightOn 4 ue SET DO EQU 0x200 EA L BASEADDR pt E L CONTROL pt temp 0 rtnvalue LAMPON temp BEQ IsLightOnEXIT OVE L 1 rtnvalue LightOnEXIT RTS OVE L AND L But if you adjust code where values are pushed onto a constantly changing stack it s easy to introduce error Having a fixed stack frame size deter mined by the maximum number of parameters to be passed avoids errors and offers speed advantages Space is allocated on the stack for all local variables despite the fact that many variables are optimized directly into registers This helps with code maintainability There s no speed disadvantage for adjusting the stack pointer by 200 rather than 48 bytes If stack space is limited remove the unnecessary storage locations
106. ion Since the FIR filter performs addi tional low pass filtering of the signal it removes high frequency noise that was present in the original input signal and the shaped noise that was added by the quantizer in the delta sigma modulator This filtered output is now bandlimited to the original band width of interest so you can reduce the sample rate to just twice this value by not bothering to calculate the extraneous intermediate samples DELTA SIGMA DAC The job of the delta sigma modulator in the DAC is to tum a series of integers representing a band limited signal into an oversampled one bit signal that can be averaged by a simple low pass filter at the output Here the delta sigma modulator is implemented in the digi tal domain and the integrator is just another digital filter IIR The overall structure is shown in Figure 5a 70 Issue 101 December 1998 i Zero Difference Mtegrator quantization Output signal Zero input signal There are two unwanted signals in the output of the DAC images of the input signal created by the sampling process and noise introduced by the delta sigma modulator see Figure 5b To help eliminate the images the delta sigma DAC starts with a digital low pass filter that acts as an interpo lator that oversamples the digital signal The filter is flat in the spectrum of interest and the signal is known to have no energy in its transition region So the filter has no effect
107. is varName Extended Attribute Normal Attribute Extended Attributes RARRAY RNONE RNV RTOKEN tended Attributes can be combined by ORing the keywords varName VARARRAY VARTOKEN Normal Attribute Normal Attributes RBIT Bit flag value Cannot be an array BYTE one byte value DOUBLE double precision floating point value DWORD four byte value FLOAT floating point value READABLE NG one byte character array RING two byte unicode character array RING two byte wide character array D two byte value TEABLE Attributes can be combined by ORing the keywords e VARARRAY VARTOKEN VARBYTE VARREADABLE RITEABLE CNM nam ADDO ADDADDADADDADADDD ARNONE VARBYTE VARREADABLE VARWRITEABLE ARNONE VARBYTE VARREADABLE VARWRITEABLE DECEMBER 1998 LEED C 65 everybody up and wait for work The real work is performed in the two functions shown in Listing 7 called Poke and Peek These functions are tied to EMIT using a configuration ini file Peek and Poke are defined as exports in the ini file along with any variables tied to EMIT s GUI widgets Since Peek and Poke are defined in the configuration file EMIT can generate code and addresses for them in its internal tables Data is transferred between the 66 PIC functions and EMIT via two buffer areas within EMIT These buffer areas are addressed as payload and replydata the receive and send buffers EM
108. is formatted a Linux file system is installed with the mkfs command in Linux O nce the file is made the floppy ismounted anda boot directory that contains the Linux kernel is installed The boot directory also contains the LiLo table image Of course for a boot floppy you only have one boot option to boot Linux The config file featured in Listing 1 is what I d use to configure LiLo for a floppy Now if the floppy is booted in your embedded system the system BIOS loads the LiLo boot loader which consults its table of bootoptions On the console LiLo prompts for an image name to bootand it will timeout and boot the default image if the user does not enter anything That s configurable of course and LiLo can boot the image directly withouta prompt if you want However providing the prompt lets a user enter options and flags for the kernel and can be used to debug things or change the location of Linux s root partition Once LiLo determines which image to boot itloads the image into memory and transfers control to it If no options are specified the Linux kernel uses whatever file system it was booted from as the root file system That s important because the kernel has to find the device entries for the console and any other device to be used The kernel then executes inuxrc or sbin init depending on whether the file is running from RAM disk l Il get back to that later on If the system can t find sbin init
109. isting 2 continued equ Code TMRO_OVF tst tst brne tst brne ERROR ov ov borne L ERO 1 test the high count byte sbranch if CNTLH lt gt 0 stest the mid count byte sbranch if CNTRM lt gt 0 stest the low count byte sbranch if CNTRL lt gt 0 sreload the low count byte sreload the mid count byte sreload the high count byte sraise PB tput sdone with is interrupt slower PB t even if already there sexit thro e place s decre t t byte affects carry sbranch if rrow T exit place s decre i t byte affects carry sbranch i rrow sexit t place decreme i t byte affects carry sbranch i rrow if error reload T exit t g place Circuit Cellar INK Issue 101 December 1998 77 GETTING YOUR WINGS What good s a programmer with nothing to program Here s a little application you may have made using a 555 timer and a big CAP see Listing 2 Using a 555 as a long duration timer requires a hefty sized ca DB 25M i DATAS cis 4 flow The 8 bit timer has a prescaler with five selec tions 0 8 64 256 and AUTO DATAL DATAZ 1024 oodd d coooooopooo ui 5052323 RST UCE A separate watchdog circuit employs an onboard 1 M Hz oscillator t
110. it starts up the shell the command line interpreter for Linux Although LiLo is flexible and complex it requires a Linux file system to find its tables and access the Linux file system This can be a problem Because Linux bypasses the BIOS to access devices like the floppy disk and hard disk it can t access devices like a flash memory based disk unless they look like one of the more traditional devices So installation of LiLo on a flash memory based file system is almost impossible Of course if you use an ATA compat ible flash disk like the one from SanDisk shown in Photo 2 this is no problem To the system the disk will look like a fast IDE drive and any OS including Linux that knows how to access an IDE drive will be able to deal with it Use the same technique here as when you generated the boot floppy SanDisk flash disks are popular in high end digital cameras and PCMCIA adaptersare avail able at many places carrying such cam eras A Linux boot disk can be built with a SanDisk on any notebook thatruns Linux and has a PCMCIA adapter My embedded system also needs a SanDisk interface either via a PCM CIA or PC 104 adapter or through a Motorola NLX 55 Pentium based SBC with an em bedded SanDisk interface If you have flash based memory al ready on the embedded system board but don t want to use an ATA flash card or SanDisk you can try a Linux boot method thatdoesn trequire a Linux based file system He
111. ity and safety that it promises to bring to portable computers medical equip ment consumer products and more SMART BATTERY SYSTEM Created by a group of leading com panies to improve portable product performance SBS is based on a set of standards 1 maintained by the Smart Battery System Implementers Forum As Figure 1 shows SBS consists of the system management bus SM Bus the SM Bus system host the smart battery the smart battery charger and the smart battery selector SBS based products integrate these key compo nents into a system that can maximize product service life while providing accurate and timely equipment status information to the user SYSTEM MANAGEMENT BUS The SM Bus provides the physical medium and command protocols that support the transfer of information between SBS components Envisioned as a low cost low bandwidth commu nication link it connects various devices within portable equipment SM Bus includes a physical medium based on the C bus developed by Philips Semiconductors although some of the electrical characteristics differ 1 The I C bus is a two wire open collector multimaster multidrop serial bus that uses clock and data signals to communicate with up to 127 devices on a single bus Using a serial bus reduces the pin count and cost of devices attached to the bus And it reduces PCB real estate requirements for pathways to connect the devices Devices on an SM Bus may act a
112. kControl Block see Listing 3 describes a task exec keeps all tasks in a circular linked list and a global variable keeps track of the current task To choose the next task to run exec follows the next pointer field of the current task and sets the current task variable accordingly To ensure that there is always at least one task to run the system creates a null task It calls UEXC_Defer in an infinite loop enabling other tasks to run If no other task is there the system runs this null task indefinitely A task is identified by its task ID which is kept in the tid field ticks Circuit Cellar INK task id task state do not use enum since compiler may allocate more space how many ticks does task execute function to call for that task stack low value stack high value current value of stack pointer is the number of ticks that the task should execute before scheduling occurs i e its timeslice value current_ ticks is the number of ticks left in the execution of this task func is the pointer to the C function for the task The stack start and end values are for debugging purposes such as detecting stack overrun sp is the current value of the stack pointer It must be within the range of the start and end stack values GLOBAL VARIABLES As most programmers have learned global variables are generally not part of good code design But there are situations where t
113. lave Address stoP Send Byte Command Start Slave Address Data Ack sto Receive Byte Command Star Slave Address Data Nack stoP Write Byte Command SMBus system host Smart battery charger Smart battery selector Smartbattery Table 1 SMBus includes these I C slave address assignments for standard SBS devices operate It also guides the built in power management system in selecting the best algorithm to extend battery life The data includes member elements that indicate present battery operating parameters like battery pack tempera ture and terminal voltage and current Additionally it predicts battery operation such as remaining capacity and runtime to empty Also it identi fies the battery manufacturer and chemistry as well as controls battery operation such as remaining capacity and remaining time alarm levels and operating mode controls Although all SBS data in a smart battery is readable from other SBS devices only a few alarm mode and rate parameters are writable from the SM Bus Most parameters are measured or calculated within the battery pack Other data elements like manu facturing date serial number and device chemistry are programmed into the battery pack electronics during manufacturing l Start Slave Address Command Code Ack stoP Write Word Command l Star Slave Address Command Code A
114. lem at three levels In Figure 5 these levels are described as system architecture software architec ture and object architecture The first layer refers to hardware elements like boards buses intercon nects and subsystems Software archi tecture refers to the system software and RTOS issues like concurrency and persistent storage modeling Finally in an OO environment the application layer in the software is defined as a collection of objects in the form of a Class diagram shown as the object architecture layer in Figure 5 UML offers the Class diagram not only as a means to define the system s logical architecture for building the OSD in Figure 4 but also for detailed design of each class It also shows the details of relationships among differ ent classes in the system Once sufficiently defined and developed the Class dia gram is the basis for code gen eration As the attributes and d Configure for data compression the AT command processor Use Case is broken down to show response and reply timing information automated code generator from the modeling tool The class code in Listing 1 contains not only the attributes and operations of these classes but also a reference to the instances of other classes that they associate with eg Async_I 0 asso ciates with the instances of AT_Com mand_Processor DataManager and ErrorManager Although the Class diagram gives software engineers a powerful tool
115. lid but immutable Clearly with design cycles crunching ever downward something has to give ADAPTATIONS Almost every engineer has run into the Von N eumann Harvard problem Generally the solution falls into one of two categories simply executing tokens stored in some form of non volatile memory NVM or swapping banks of code and data spaces so one bank can be written while the con troller executes from the other The BASIC Stamp from Parallax is an excellent example of token execu tion Ours is built from a PIC 16C56 and 93C56 NVM When write a program in PicBasic and upload it to the Stamp I m really sending tokens to the PIC to represent commands like FOR NEXT and GOTO The PIC stores these tokens in the NVM Later the PIC executes these tokens by fetching them from the NVM figuring out what each token means and carrying out the instruction These PicBasic tokens are not op codes native to the PIC the PIC is executing native code out of its ROM to interpret PicBasic tokens on the fly It s like getting a secret message and using your decoder ring to read it The overhead in token processing is immense An instruction such as A B may take hundreds of times longer than it would if the device were executing native opcodes Still this method is inexpensive and until recently was the only real solution But its Achilles heel is obvious what if the bug is in the interpreter Fortunately Parallax h
116. los i on lt AN PTI T CIRGUIT CELLAR 101 DECEMBER 1998 i i ih k J 5 rm h i Achieving Better Design Communication with UML C and Assembly Language When to Use What A Real Time Multitasking Executive PICs and PCs Come Together the Embedded Way wE T 3 95 U S x 4 95 Canada L e4MANAGER The Word is Communication hen think of programming it occurs to me that it s just one of many types of communication Whether you re trying to get information from computer to computer or from person to computer it s still the same goal the sharing of information that will hopefully prove useful to someone somewhere Maybe one of the reasons that useful communication has become so relevant to me has to do with my recent trip out to the Embedded Systems Conference in San Jose And this has more to do with getting useful information from person to person On the one hand Circuit Cellar had its own announcements to make had the privilege of speaking at a breakfast hosted by Motorola s Semicon ductor Products Sector The point of the event was to introduce Motorola s new family of 8 bit flash based 68HC908GPxx microcontrollers with the first product being the GP20 But my agenda was the launch of Design99 Circuit Cellar s eleventh annual design contest Prize wise it s the biggest design contest we ve ever offered with five 5000 first priz
117. ly code initialization routines Transfer control to C main Trap back to system kernel Circuit Cellar INK The 8 bit wide Transmit and Re ceive registers communicate with a small hand held screen and touchpad The Flash and Darken 16 bit register values reload the timers that control the rapid flash lamp and glasses The control register is 32 bits wide with Readready and Writeready bits for the serial communications line registers being bits 0 and 1 respec tively The activation bits for the Flash and Darken timers are bits 4 and 5 Interrupt handling information is stored in bits 16 31 If the Overheat warning bit bit 8 is set the rapid flash lamp controlled by bit 9 must be switched off GETTING STARTED The code for the main components of the first GLOB device prototype is given in Listings 1 2 and 3 main c see Listing 1 has amain function that calls the assembl y language pro gram void CallAsm void Also included in main c isasimple C utility void ShowTitle void that is called directly from the assem bly language routine CallAsm init s in Listing 2 contains the 68k code needed to establish the sys tem stack used by both C and the custom assembly code This code is activated during startup before main is called Various important initial izations e g ResetInit are also necessary before calling main After main exits program control returns to the embedded system ker
118. m In the world of PCs the Mac OS until OS X is an example of a cooperative multitasking system and so is Windows 3 1 and below except strangely for the DOS boxes under Windows 3 1 In a preemptive multitasking system eg Windows NT the system inter rupts a running task if other tasks must be run A preemptive system is more powerful than a cooperative one because it s easier to program and it enables tasks to run more fairly Under a preemptive system priori ties can be assigned to tasks so the scheduler will run higher priority tasks first A high priority task that is waiting for a resource may interrupt a lower priority task if the resource becomes available The multitasking executive we describe here is the preemptive type Despite the benefits of a multitask ing executive it s often not cost effec tive for most simple programs or for people on a budget to purchase a full blown multitasking executive Here we show you a small multitask ing executive aptly named exec pronounced myoo exec written in ANSI C and some assembly routines The supplied code is written for and tested on a Motorola HC11 but it should be easily ported to other micro controllers of comparable power The code is quite small in fact compiling to only 700 bytes using the ImageC raft ICC 11 HC11 C compiler exec is a preemptive multitasking system but to keep the code small its tasks all have the same priority level
119. mm can be attached to many surfaces They can also be combined with plastic or metal films for in creased stiffness or for added protection from their environment The software is simple to use and easy to interpret It is possible for users to read static or dynamic forces in real time or record a movie and view the information in a choice of graphical displays The information can then be viewed as a strip chart bar graph analog meter or digital display The FlexiForce ELF sells for 299 and custom sensor designs are available FlexiForce 617 269 8373 Fax 617 269 8389 www tekscan com 12 Issue 101 December 1998 Circuit Cellar INK December Design Forum password Code Your magazine enjoyment doesn t have to stop on the printed page Visit Circuit Cellar INK s Design Forum each month for more great online technical columns and applications Here are just some of the great new on line articles you ll see in December Columns Silicon Update Online The End of Architecture Tom Cantrell Lessons from the Trenches Getting a Head Start on Software Development Setting It Up for the Target George Martin Forum Feature Articles When Can You Sell an Idea Without Losing Y our Patent Rights Breffni Baggot A Serial Word Generator Raymond Dewey PIC Abstractions Design Abstracts from our Design98 Contest A PIC12C508 Multichannel Remote Control Transmitter Robert Larson D
120. nclude displaying network status importing web pages and text from RS 232 or RS 485 serial lines and displaying dynamically changing data The system is ideal for data acquisition and control The FlashTCP Server comes with DO S and connects to 10BaseT Ethernet networks Features include four PC compatible RS 232 serial ports one configurable as RS 485 a bidirectional printer port LPT1 34 parallel I O lines and onboard switching power supply accepts 7 34 VDC Italso offers a Y2 K compliant clock calendar system watchdog timer 512 KB SRAM 512 KB flash memory and a socket for a 512 KB flash memory or RAM disk Cards supporting A D and D A conversion isolated I O and GPS are also available Software can be developed using Borland C C Microsoft QuickC and QuickBASIC or development tools for DOS target systems Developers can easily upload compiled code through one of the serial ports or via ftp and Ethernet The FlashTC P ships with preinstalled web server user manual and schematic and is priced at 329 in 100 piece quantities A developer s kitincluding the FlashTC P preinstalled software cables AC adapter utilities disks manual and schematic costs 469 JK microsystems Inc 530 297 6073 Fax 530 297 6074 www jkmicro com QUAD DSP BOARD The Silvertip Quad PC 104 combines four 40 M Hz ADSP 2106x SHARC DSP processors 512K x 32 SRAM and 1MB flash memory on a standard PC 104 form factor board Also
121. nction UEXC_Kil1lTask is called with the task s ID void UEXC_Defer void gives up the rest of the timeslice and lets other tasks run This function calls an assembly routine to construct an interrupt stack frame so that the task can be resumed by using Return FromInterrupt This process is consistent when a task is interrupted by the timer and its timeslice runs out void UEXC_KillTask int tid is a function that kills a task with the Listing 4 This trivial program tests uexec s basic functionality Two tasks are created and each one prints out a different character on the output include uexec h unsigned char task_zero_stack UEXC_MIN_STACK_SIZE unsigned char task_one_stackLUEXC_MIN_STACK_SIZE void Zero void ile 1 tchar 0 One void ile 1 tchar 1 void main void UEXC_CreateTask Zero task_zero_stack sizeof task_zero_stack 0 UEXC_CreateTask One task_one_stack sizeof task_one_stack 0 UEXC_StartScheduler Circuit Cellar INK ID tid It searches the task list to find the matching task and reclaims its storage after it unlinks it from the list void UEXC_HogProcessor void hogs the processor and gives the current task another timeslice If this function is called repeatedly before its timeslice is up then no other tasks except for the interrupt driver function are run It simply assigns the current_ ticks field of the task control block with the ti
122. nd output functions of O port pins CIRCUIT CELLAR INK DECEMBER 1998 timer mode with prescaler 32 weak pullups unmask peripheral interrupts and TMRO unmask USART TX and TX interrupts Following along under InitMicro Controller the next step is to set up the Option register This register enables the programmer to define port B pull up sta tus interrupt edges timer clock sources and timer prescaler values 64 Weak pullups on port B are enabled in the application and the timer is prescaled by a value of 32 Writing a binary 01000100 to the Option register does it all The next logical step is to enable or unmask any interrupt options you deem necessary for the application Notice that the serial communication pin interrupts are unmasked but not enabled emWare uses a round robin approach Each part of the EMIT program must have equal access to processor resources Oth erwise data may be lost and processes may hang Later on you ll see that the communications resources are being polled About the only thing left to do now is O port initialization Here simply set ting the ports to O is sufficient Listing 6 shows the final three init procedures The call to set the ports to O is found under loopo By convention emMicro code is in cluded in the source code so its routines can be called from within the program Any included files are declared at the end of the user written application code One such r
123. nd the necessary modules for your application you need to compile the kernel Yes full sources for the kernel and many modules and device drivers are provided in Linux To compile the kernel once itis config ured use the make utility Usually the command make vmlinux will compile and link everything that you need But if you have modules thatare required by the kernel you also need to compile the modules in a separate step using the command make modules Once everything is made you end up with a kernel image file N ext compress the kernel so it takes up less space First use the command make zImage Com pressing the kernel is done with gzip a compression tool and algorithms devel oped by the GNU project 54 Listing 1 In this LiLo configuration file specify that there is only one image named linux and that the prompt should timeout after 5 s We can use this configuration to install LiLo on a boot floppy if we use the invocation lilo C lilo conf r mnt assuming the floppy is mounted on mnt boot dev fd0 map boot map install boot boot b prompt timeout 50 image boot vml inuz label linux root dev fd0 BOOTING FROM FLASH N ow let s look at how to get Linux on a boot device In normal Linux desktop installation the kernel and application programs are stored and booted from a hard disk This situation is possible either in a dedicated Linux installation where Linux is the only OS on the di
124. nd the reconstructed wave form has much higher distortion levels When the level gets down to one or two quants a sine wave signal comes out looking more like a square wave When the level drops below one quant the signal disappears altogether this is known as the fade to black or fade to zero problem 1 bit Input signal samples ri Quantizer and sampler b 1 bit gt er samples n m bit coefficients A output Figure 4a The ADC uses an analog delta sigma modulator to turn the waveform into a high speed bitstream which is then reduced digitally b The digital FIR filter both reduces the sample rate and increases the word width Circuit Cellar INK Figure 6 shows two scenarios of what happens as a signal fades An undith D 9 Modulator ered signal is shown in Figure 6ai and Scan Soren seneel Figure 6a ii shows the result of digi inter i Le Quantizer Switched RIG tizing it The bottom two traces give a Paie m Ea gt titer eter P output rough idea of how the ear interprets 7 x this signal Figure 6aiii is a short term High speed High speed clock cloc moving average which shows the tone you perceive and Figure 6a iv is the difference between Figure 6a ii and A Amplitude Sin x x distortion wie f
125. nel via a TRAP instruction and an associ ated parameter Equivalent software interrupts that transfer control back to an OS kernel or monitor can be found on other processors In the init s assembly code note that many compilers use the function name _main rather than main when transferring control to the C function main This coding convention uses a leading underscore and is familiar to anyone who s ever received an error message after accidentally linking C code segments that contained a miss ing function or misspelled name Naming conventions are language specific Anyone attempting to link legacy FORTRAN code _MAIN_ dis covers this quickly Issue 101 December 1998 33 Register Name Register Offset But it s possible that an Control 32 bit 0x 00 earlier subroutine e g Transmit Receive 8 bit 8 bit O x 04 e main may rely on the Flash time 16 bit 0x08 original value stored in AO Darken time 16 bit 0x 0A for some critical but Table 3 The GLOB device register characteristics sizes and offset were chosen to emphasize some of the problems of interfacing C and the device hardware N ote that the utilities are provided in afile named main c in C rather than main cpp in CH The naming convention to handle the function overloading possible in C is far more complex than for C functions The final component is the asm s file in Li
126. ng on chip board and systems design and marketing in Silicon Valley for more than ten years You may reach him by E mail at tom cantrell ircuitcellar com by telephone at 510 657 0264 or by fax at 510 657 5441 REFERENCES Hot Chips Conference www hotchips org Hot Interconnects Conference www hoti org SOURCES PA8500 H ewlett Packard 800 452 4844 650 857 1501 www hp com usa SV1 Silicon Graphics Inc 800 800 7441 650 960 1980 Fax 650 933 1010 www europe sgi com mathe HER AINTERRU PT Embedded Happenings d wi hew Talk about whirlwind trips and accomplishing a lot in a short time Last week was one of those times In one week we exhibited at the San Jose Embedded Systems Conference co sponsored the new Embedded Internet Workshop and announced Design99 Circuit Cellar s latest design contest jointly sponsored with Motorola In the middle of all this organized chaos the six of us attended workshops and had scores of meetings with companies and authors The result will be some fantastic editorial for the future Of course the frantic pace taught a few lessons too Elizabeth learned not to schedule meetings 90 minutes after touching down from a cross country flight Tom learned that there s a practical limit to the number of meetings and presentations that one person can attend in one day and Jeff and learned that some of this might actually be fun again Jeff and are your basic travel g
127. nimal host intervention Ap plications range from data acquisition and parsing communication protocols to using itas an intelligent virtual peripheral thatcan execute complex front end com putations process control loops and logi cal sequences A 20 MHz Microchip P1C16C74 RISC microcontroller controls onboard circuitry and executes any application specific computations or logic operations Standard features include two 12 bit and three 8 bit 0 5 VDC analog in puts and two 12bit 0 4 095 VDC analog outputs This board also has eight I O rack compatible digital chan nels advanced timer functions PW M capture compare 2 KB serial EEPROM shared interrupts one PlC supervised RS 232 485 serial communications port eee AA vey a tt kan i DCOM TECHNOLOGY FOR WINDOWS CE Annasoft Systems has announced Intrinsyc DeviceCOM an implementa tionofDCO M distributed componentobjectmodel for W indowsCE DeviceCO M makes it easy to create and deploy client server distributed applications and it extends the current capabilities of the W indows CE operating system Factory automation transportation and pointof sale applications are included Annasoft supports vertical market DCOM based standards by offering DeviceC O M application kits The DeviceC O M Q uickstartO DK O EM developer s kit gives developers everything necessary to create distributed applications on Windows CE The kit requires no programming and implements all
128. noise signals suitable for dith ering Important parameters include the choice of probability density func tion PDF the choice of frequency spectrum and the choice of amplitude how much signal to add Dither signals affect the original signal in two ways They make the system transfer function more linear and change the system s noise characteris tics by masking modulation effects A signal s PDF is a measure of how likely it is to have a given value sort of like the histogram constructed for the sine wave Some important PDF curves are shown in Figure 7 The Gaussian curve is a good model for many natural noise sources whereas the uniform and triangular curves are easy to generate in the digital domain using random numbers The latter have definite minimum and maximum values beyond which the PDF is zero but the Gaussian PDF is nonzero but very small all the way out to positive and negative infinity The dither signal s amplitude is a measure of the width of its PDF relative to the full scale values the system can handle For uniform and triangular PDFs this measurement is given as the peak to peak amplitude For the Gaussian PDF a statistical measure usually standard deviation is used For any of the three PDFs the best linearity and least noise modulation occurs when the RMS value of the random signal reaches half a quant The difference comes down to how much higher the peaks of the signal are than t
129. nutes Perhaps more disturbing was how many potential panelists turned him down Sure the reasons were purport edly innocent too busy on vacation But the most common excuse was prefer not to anger Microsoft Sounds like fear and loathing in Silicon Valley Anyway he managed to come up with a panel composed of a lawyer and various tech types who seemed like many in the audience rather unhappy with Microsoft Complaints Piece counts KP vs K KR vs KP Address generators XORed piece KQ vs KP locations for each piece type KRP vs KP Figure 5 The IBM chess chip supplements brute force move evaluation with strategy embodied in an endgame ROM Circuit Cellar INK Issue 101 December 1998 were along the line of got no class software sucks and done me wrong have to credit the lawyer Mr lan Feinberg for generating more light than heat Though no fan of M icrosoft he did point out that attempts to break it up can t rely on historic antitrust reasoning Standard Oil s turn of the century no no was an attempt to mo nopolize by acquiring all competitors while Microsoft is largely self grown More recently the breakup of AT amp T was actually about deregulating some thing government created in the first place Is the answer now to impose government regulation on Microsoft find myself somewhere in the middle sometimes curs
130. o evaluate different techniques CIO EAUCAOREE DELTA SIGMA IN GENERAL couple more advanced Delta sigma converters are basically one bit converters and therefore enjoy i ini some of the advantages of PWM that topics SO to finish up covered last time They require a very this series DEWIT small amount of analog circuitry and have excellent linearity characteristics They re based on the same basic gives US the details on concept as PWM a binary two level mt signal with a variable duty cycle can delta sigma converters represent many different average volt i i age levels The trick is noting that there and dithering are many choices of binary waveforms that have a given average value Suppose you have a PWM of the type I discussed last month which has a six bit counter Its sample rate would be Y s times the clock rate That is if you give it a clock of 512 kHz the sample rate will be 8 kHz If you set the other input of the comparator to 47 it generates the upper waveform shown in Figure 1a 68 Issue 101 December 1998 Circuit Cellar INK which is high for 47 clocks and low for 17 clocks making a 64 clock cycle The FFT of this waveform shown in Figure 1b gives you an idea of the kind of filter you need to turn this signal into a steady analog value FFT bin O represents the average value of the waveform over one full cycle one sample and has the desired value of 47 But the nearby bins show signi
131. o give eight timeout choices between 16 and 2048 ms This can be pacitor And even then accuracy is sorely lacking You can make a quick presettable long duration timer using an AT 9052323 micro and a 32 kHz crystal One of the three I Os be comes the output and the remaining I Os are used as timing selectors chose 1s 1 min 1 h and 1 day as the four output choices These can be selected by grounding or leaving open the PBO and PB2 pins set up as inputs Each input can have a weak internal pullup enabled to reduce parts count chose PB1 to use as the output because it was used as the MISO output when programmed the device through the SPI interface 78 Issue 101 December 1998 8TLI SCK XTL2 MISO GND MOST The reset input has an internal pullup and begins the power on timer once V has reached 1 5 V At this point the AVR microcontroller s ex ecution begins at address 0000H Two interrupt vectors are available The first is at address 0001H for exter nal interrupts that may be rising edge falling edge or low level triggered through PB1 The second interrupt vector is at address 0002H for the TIM ERO over Circuit Cellar INK Figure 2 Powered from the parallel port s upper data lines this programmer can be accessed using a BASIC program used to keep your application on the straight and narrow or to wake up the micro from its sleep mode T
132. o step process The master first writes the com mand code to the slave device so it can tell the slave what information it needs Then the master without generating a stop condition sends a new message to the slave reading the data The first byte indicates how many data bytes are to follow SM Bus slave devices may use any or all of the above command protocols Supported command protocols are defined in the appropriate SBS compo nent specification SMBus hosts should support all command protocols Although its initial use is to connect SBS devices SM Bus can be used for connecting a wide variety of devices The protocols meet most C bus communications requirements and are worth considering even on non SBS or SM Bus related projects SMBus SYSTEM HOST The SM Bus system host is the equipment laptop PC cellular phone video camera etc that communicates with SBS devices over the SM Bus It s powered by the smart battery In a laptop PC the host is the laptop s processor In other products the host might be an embedded microcontroller or microprocessor Whatever form it takes the system host provides the interface between the user and the rest of the power manage ment system The host s computing power can be used directly or indirectly to determine user power requirements Its SM Bus communication capability enables the system host to interact with the smart battery to determine slave reading two
133. oduct design and manufacturing He may be reached at jeff bachiochi circuitcellar com REFERENCE Atma AVR910 In System Program ming App Note 0943B B 1997 SOURCE AVR AT90S2323 Atmel 408 441 0311 Fax 408 436 4200 www atmel com Issue 101 December 1998 79 SILICON UPDATE Tom Cantrell Hot Chips X Files 80 It just wouldn t seem like summer if Tom didn t make it to Hot Chips And it just wouldn t be winter if we didn t read about everything he saw and heard SIMDs Deep Blue copyright law and Microsoft what a mix Issue 101 December 1998 Circuit Cellar INK he annual Hot Chips conference has become part of my summer ritual in the Silicon Valley When I see the newly minted Y ups drop the tops on their Beemers know the latest and greatest IC wise is right around the corner Perhaps it s the idyllic environs of the Stanford University venue The presentations are given in the stately Memorial Auditorium which with elevated theater seating is much nicer than the typical conference room Hungry Instead of schlepping over to some aptly named concession to good taste stand just step outside for excellent catered dining in the tree shaded Dohrman Grove Want to stretch your legs You can wander over to Hoover Tower or the Rodin Sculpture Garden Perhaps I m attracted by the non harried and noncommercial nature of the conference delivered under the auspice
134. of subsystems and is a good representative of a real time embedded system In this article discuss the design at a system architectural level anda detailed design level exploring the issues that arise when using UML for modeling also consider how the UML notation can be extended to better address the basic characteristics of real time systems The diagrams are the result of using extensions to UML and provide more effective communi cation among engineers THE BIG PICTURE Arguably system architecture demands more collaboration and agreement from all of the teams than any other part of the project Because the specifics of the underlying system are vague at this stage all engineering teams view the system at an abstract level t _ In UML Use Case diagrams capture the system requirements into numerous group ings called Use Cases Terminal operator Transfer data T Terminal Application Send data over phone lines Perform data uses A Interface with compression ED z phone lines Telco This functionality is descri bed from the perspective of a system user or actor An actor though not necessarily a human operator represents a user that interacts with the system In Figure 1 Teco a tele phone company is an actor because it interacts with the phone ine interface in the modem Use Case Figure 1 also represents other Use Cases as recognized for an asynchro nou
135. ols and adjunct professor of man agement and information technology at National Louis U niversity in Chi cago He was manager of embedded systems database development at Aksys Ltd and president of Irfnet Irv has extensive consulting experience in helping companies implement model ing and design solutions You may reach him at irvb artisansw com REFERENCES M Fowler et al UML Distilled Applying the Standard Object Modeling Language Addison Wesley Object Technology Se ries June 1997 A Moore and C Niall Real Time Perspective Overview Artisan Software Tools Capitola CA 1997 A Moore and C Niall Real Time Perspective Foundation Artisan Software Tools Capitola CA 1997 A Moore How Do Map Objects to Real Time Tasks and Vice versa Artisan Software Tools Capitola CA 1998 SOURCE Real Time Studio Artisan Software Tools 831 475 5554 Fax 831 475 3195 www artisansw com Circuit Cellar INK Issue 101 December 1998 31 some Assembly Required FEATURE ARTICLE Michael Smith Assembling C Code for Your Embedded System The most important rule for programming in assembly language know when not to When time and money are riding on how long it takes to develop debug test and implement code sometimes it s in your best interest to link in some C 32 Issue 101 December 1998 t might seem strange but the best advice you can give someone learning
136. ong time flight tested indeed It still makes money for some of us old airplanes still fly too It has the poten tial to make money for our children and children s children imagine the next gen eration of jet aircraft But what s so great about it For the enlightened the Internet is close to the Almighty in terms of information as it relates to power Whoever owns and comprehends the information the quickest holds the power to use it to their advantage Nathan Bedford Forrest knew this long ago He was consumed with fighting a war but the stakes were the same Remember the firstest with the mostest quote It still holds true With that let s take some of the emerging technology within reach and put some flight tested hardware to work PICING UP Last month when I laid down the ground work emWare supported the 8051 micro controller platform exclusively Now they re porting the 8051 paradigm to other platforms like Microchip s PIC don t know about you but that s what I ve been waiting for With this article you ll be the firstest with the mostest I ll show you how to launch the PIC16C73 into emWare land And if you re wondering why chose the 73 welcome to PIC16C73 101 THE PIC16C73 AND emWARE I m not going to go into finite PIC theory here Instead l Il go over the points that DECEMBER 1998 t NDP C make the PIC16C73 suitable for an emWare port First of all to control the
137. ool API In this section we present the user callable functions The function proto types and user definable macros are in the file uexec h These functions are written in ANSI C and they shouldn t need modifica tion to compile for other processors similar to the HC11 or under differ ent compilers As well some of the internal C functions shouldn t require any modification for porting purposes The function int UEXC_Create Task void func void un Signed char stack unsigned stack_size int ticks creates a task given the function func Each task must have its own stack given by the argument stack This stack is the lowest address of the array i e address of the zero th element Since stack usually grows from high addresses to lower addresses the size of the stack is needed and is given by the argument stack_size With the stack and stack size the stack pointer can be checked against the bounds If you port exec to a processor that needs stack alignment you need to align the stack properly ticks is the number of ticks in this task s timeslice If it is zero then the value given by the macro DEFAULT_ TICKS is used UEXC_CreateTask obtains a task control block from the free list initial izes it with the supplied arguments and links the task control block into the circular task list This function returns an integer task identifier If the task function returns then it acts as if the fu
138. or the return address is part of the stack frame the programmer establishes Many DSPs use a hardware stack for Listing 6 The function ong int ReturnTimerValues void to access a 32 bit hardware register works correctly at the assembly code level but not at the C code level EXPORT EXPORT _ReturnTimerValues ReturnTimerValues ReturnTimerValues _ReturnTimerValues ILAR pt SET AO rtnvalue SET DO FLASH EQU 0x08 MOVEA L BASEADDR pt long int ReturnTimerValues void register long int pt register long int rtnvalue define FLASH 0x08 pt long int BASEADDR Grab both 16 bit registers at once pt pt FLASH MOVE L FLASH pt rtnvalue RTS IAT Circuit Cellar INK return pt return address storage Other proces sors modify the stack frame by the adding a return address onto the stack via call to subroutine Some processors have stack pointers that point to the last used location while others point to the next empty location The assembl y l anguage pro grammer must ensure correct stack use to avoid passing or using the wrong parameter Prior to exiting the calling subroutine the local variables and out parameters must be removed from the stack possibly using a frame pointer register A6 ARRAY OPERATIONS Listing 8 shows the arrays that can be described in C It s important to recognize what happens at the assem bly code level for each type of array st
139. ore than one way to incorporate hardware properties into the System Architecture diagram In this case the values refer to the RS 232 interface on the modem controller board Circuit Cellar INK The challenge in coordinating these disciplines is compounded because all three have different concerns use different tools and work somewhat independently of one another The system engineer in an effort to refine system requirements and assess feasability is concerned with state modeling of the control system or communications protocols The hardware engineer tends to think in terms of processors and circuits within the domain of schematic capture ASIC design VHDL circuit simulation and board layout The software engineer is thinking about functional decomposi tion or an object model There s no proven methodology to bridge these disciplines and implement a more collaborative system develop ment Most organizations rely ona document or drawing tool to capture system architecture Although keeping that document current is challenging making it rel evant to the software engineer is more difficult Few software engineers read schematic diagrams or other hardware documents when considering how to interface their software to the hardware In this article consider the possi bility of coordinating system hardware and software development by using object oriented OO technology specifically the Unified M odeling L
140. otof effort A compromise is sought between systems that are general pur pose and those thatare totally customized to one application ume in drive A has no labe ume Serial Number is 2463 1AD1 54619 09 30 15718 09 30 32208 08 29 429371 08 29 166233 08 29 285 08 29 698 434 bytes and com exe exe inuz bat file s 4 400 bytes free Figure 1 These are the contents of a DOS based Linux boot floppy The DOS utility 1 0ad1in exe reads the Linux kernel image vm inuz and the RAM disk image initrd into memory and then transfers control to the kernel to boot it This file can run out of a flash based file system DECEMBER 1998 REED PC 993 6 993 6 998 16 998 16 998 17 998 19 So rather than excessively customiz ing or writing something from scratch let s look at how to embed Linux without too much fuss REDUCING THE KERNEL M ost Linux distributions deliver a Linux kernel that is configured to be as general purpose as necessary and yet still supportas many different devices as possible That s fine for mostdesktop applications because there s memory and disk space to burn However to embed Linux the size of the kernel should be reduced as much as possible There are two techniques for accomplishing this task customize the kernel and com press the kernel image Itis possible to configure only the modules and device drivers neces sary for your applications Linux lets you do t
141. outine EmInit is always called at least once in every EMIT pro gram to initialize emWare You ll find the call to EmInit at label 100p0 Once all of the initialization is completed you can turn on the interrupts you unmasked The next label 100p3 is the main program loop It polls the serial communi cations pins for incoming bits and checks if any data is waiting to be transmitted Listing 7 Just like BASIC but different Poke Write any PIC file register movf payload0 W movwf FSR movf payloadl W pagel movwf INDF paged poke Peek Read any PIC file register movf payload0 W movwf FSR movwf replydata0 page movf INDF W paged movwf replydatal return peek CIRCUIT CELLAR INK DECEMBER 1998 My application enables the user to manipulate read and write the PIC s internal registers provided functions for that purpose that are called directly from widgets on emWare s GUI My applica tion really does nothing but loop waiting for commands from the GUI As Listing 3 shows a call to MyApp1 i cation simply executes a return from subroutine If other programmatical opera tions are needed they are performed under the MyApplication label If any EMIT processes are requested the next call to EmMicroEntry pro cesses them Once this routine is entered all table lookups and EMIT related pro cesses will be completed before this mod ule is exited loop3 is where the round robin pro cessin
142. owing nothing about chess by Feng hsiung Hsu of IBM What started a decade ago as a student project at Carnegie Mellon was cultivated into Deep Blue by IBM consider the 1997 match win by the machine over world chess champion Kasparov a remarkable success The nice thing about Deep Blue is that you don t have to be a techno guru to get it There s none of the neural network fuzzy or Al hot air you might expect Instead the machine composed of 480 custom chess chips see Photo 1 relies on brute force move evaluation to the tune of 200 million positions per second Hsu notes Speed alone might not be enough pointing out that human grand masters in serious matches learn from computers mistakes exploit the weaknesses and drive a truck through the gaping holes Deep Blue tries to create evaluation terms that overcome known weak nesses and adds hooks to deal with new ones using external FPGAs It supplements brute force evaluation with ROM based endgame logic de picted in Figure 5 that handles the well known variations that character ize the final moments of a match What s next Hsu projects that migrating to 0 35 um process from 0 6 um for higher integration and faster clock rate will enable a small array of chips plugged into a PC to beat the best the human race has to offer BEYOND CHIPS As mentioned the Hot Chips folks usually throw in a few hot topics to break up the bit banging
143. pect for the device As Figure 2 shows the parallel printer port not only programs the device but also provides power By tying the printer s Auto control line output DB 25 pin 14 to the Paper status input line DB 25 pin 12 my BASIC software can search the three Issue 101 December 1998 75 printer ports to find out where the programmer is installed Three data output bits DB 25 pins 2 3 and 4 provide the Reset SCK Listing 2 Based on a 32 kHz crystal this code provides a positive 0 5 s pulse every 1 s 1 min 1h or 1 day based on two configuration inputs and MOSI outputs to pins 1 7 and 5 AT90S2323 Prohibits use of nonimplemented instructions respectively The MISO output pin 6 include 2323def inc of the micro is monitored by the SEL gt ae Register Variables status input bit DB 25 pin 13 and i Reset vector the upper five bits of the data output jmp I External interrupt vector are dioded together to provide power fe Timer 0 overflow vector the diodes prevent incorrect data from program initializes registers devices used shorting printer outputs together The timer overflow does the rest The connections are simple enough M ee Register Variables and remember these parts program with only the normal V applied To prevent unwanted programming a particular event sequence is needed or the part will ignore all SPI commands To solve this problem the SCK line must be low before Reset
144. r AtRateTimeToFull AtRate TimeToEmpty and AtRateOK functions specified in milliamps if BatteryMode CAPACITY_MODE bit 0 else 10 mW Predicted remaining time to full charge at AtRate value Predicted remaining operating time at AtRate value Indicates if battery can deliver the current AtRate value for 10 s Cell pack s internal temperature in degrees Kelvin Cell pack voltage in millivolts Current being supplied or accepted through battery s terminals in milliamps 1 min rolling average current being supplied or accepted through battery s terminals in milliamps Expected margin of error in the state of charge calculations Predicted remaining battery capacity as apercentage of FullChargeCapacity Predicted remaining battery capacity as apercentage of DesignCapacity Predicted remaining battery capacity in milliamp hours if BatteryMode CAPACITY_MODE bit 0 else in 10 mW h Predicted pack capacity when fully charged in milliamp hours if BatteryMode CAPACITY_MODE bit 0 else in 10 mWh Predicted remaining battery life at present rate of discharge in min 1 min rolling average of the predicted remaining battery life in min 1 min rolling average of the predicted remaining time to full charge in min Desired charging rate in milliamps Desired charging voltage in millivolts Battery status word flags Number of charge discharge cycles the battery has experienced Theoretical capacity of a new pack in milliamp hours i
145. r loop that requires 36 instructions and 18 cycles for a regular PowerPC is cut to two instructions and two cycles getting your slick legal firm to bam boozle some patent office clerk with a claim that covers everything and dis closes nothing All the better if they can submarine the thing and ensure plenty of fat wallets to squeeze when it finally surfaces Copyright law is especially wart ridden with clauses for everything from pantomime and choreographic works to pictorial and sculptural works which is why you can rent a video but you can t rent a music CD or software By comparison trademark law is relatively innocuous Yeah it may seem odd that Mr McDonald can t call his restaurant McDonalds but no biggie Thanks to the com domain turmoil even trademark law is getting some notoriety lately Mr McDonald can t use www mcdonalds com either A close cousin to tarnishing some one s trademark is genericide It s not proper to say you re going to Xerox this article Instead you should say you re going to copy it Of course you should be warned that actually doing so apparently runs afoul of copyright law Use a copy machine go to jail M aybe trade secret law has the best grip on reality relying as it does on a nefarious perpetrator Recently there was a case involving a sales guy planning a job switch from company A to company B He told his current customers that company A was in troubl
146. rates the step by step response sequence in modem operation Command Connected and Update Firmware are the three possible modes of operation Issue 101 December 1998 27 Figure 4 An Object Sequence diagram provides a detailed explana Description Terminal Application DataControl ErrorManager DataControl DataManager tion of an individual Use Case Here Terminal issues an A AT command to force error correction CommandProcessing AT Command Processor TAT NS 610 us 200 ms Command processor configures the error correction object Reply with OK to the terminal AT command to force data compression Reply OK AT C3 610 us Configure for error correction Configure the data compression object Reply with OK t Reply OK tions They give the system engineers valuable tools for developing an inter active mode of the system at higher levels of abstraction However in developing real time systems especially systems with hard timing constraints timing information needs to be conveyed to the software engineers as a part of the system archi tectural requirement By superimposing the timing information on an OSD this UML diagram supports the timing aspect of the system resulting in an effective instrument of communication The evolution of OSDs begins with identifying the objects in the sys
147. re use another Linux boot loader the DOS utility oadlin exe This boot loader is simply a DOS program that loads a Linux kernel from a DOS file system With loadlin you simply copy loadlin exe and the kernel image zImage or whatever you want to call it onto a boot disk similar to flash memory You can then place loadlin zImage into your autoexec bat file and you re all set W ith this method you need DOS in stalled in your system which requires a DOS license Or you can use FreeDOS see the excellent series on FreeDOS by Pat Villani INK 95 96 Also many flash based embedded system controllers come with a version of DOS installed There s one catch when booting Linux via the DO S boot method To use devices the Linux kernel still needs some sort of Linux based file system to load the initial DECEMBER 1998 REED PC program from as well as to map device entries W ell the Linux develop ers considered this problem right from the early days of Linux and that s why Linux supports using RAM disks as the root disks You can use RAM disks with either Lilo or loadlin Linux even supports using compressed RAM disk images which take up the least amount of space on the boot media So how do you build a RAM disk image for Linux to use as a root file system You have to go back to your 5T development system and use the sequence of steps in Listing 2 Just create an empty file initialize it
148. registers The appeal lies in the fact that it s relatively easy to find and exploit parallelism in scientific and signal processing algorithms that rely on vector operations Almost all hot chips support vector ops these days the most well known example being the Intel MMX At their simplest such schemes carve a full size register into parallel subparts that can be operated on For example a conventional 32 bit ADD is extended to perform two 16 bit ADDs or four 8 bit ADDs at once The latest generation of psuedo SIM Ds pushes the concept further with wider words more operands and extra instructions Consider M otorola s AltiVec upgrade of the PowerPC archi tecture The upgrade adds a complete vector unit featuring 128 bit registers that can be interpreted as 16 x8 bit 8 x 16 bit or 4 x 32 bit data There are 162 new instructions including both the typical intra dement and the newly introduced inter element operations Figure 4 shows how the two make short work of the inner Figure 2a To ease the pain of a cache miss the HP PA 8500 and other high end chips employ both hardware and software techniques One hardware approach is a nonblocking cache that allows multiple outstanding references b while software solutions include compiler inserted prefetch to initiate cache access prior to anticipated use c Circuit Cellar INK loops at the heart of scientific and DSP code
149. requencies were boosted the deemphasis circuit at the system output has a flattening effect on the blue noise HOW TO DITHER There are several ways to add dither In the digital domain it s a matter of generating random samples with the desired distribution A uniform PDF can be created by calling for example the C function rand and scaling the results to an appropriate range A triangular PDF which is a rea sonably good approximation of the natural sounding Gaussian PDF can be generated by adding two independent uniform random numbers together If you need to write your own random number generator for a processor or to get better efficiency over the library routine Seminumerical Algorithms is a good place to start 1 Things are trickier in the analog domain There are two broad ap proaches generate random numbers in the digital domain and use a DAC followed by an appropriate voltage divider to create a signal that can be mixed in with the signal being digitized or use an analog noise source and scale its output with a voltage divider Semiconductor junctions make good noise sources Zener diodes and tran sistor junctions that are biased to the point of reverse breakdown are particu larly noisy It s more difficult to get an accurately calibrated level out of an analog noise source but with the Gaussian PDF it isn t as critical CONVERTED That wraps up this series on A D and D A conversion
150. rget micro to power our buffer Without taking power from our target we d have to use an exter nal power supply or tap the 5 V line from the PC s keyboard port Just bring an extra line out from your target and you re ready SOFTWARE We created the ISP utility ISP EXE as a Straightforward program for DOS and it s exactly what Atmel should have provided all along We chose the RESET Circuit Cellar INK Issue 101 December 1998 17 c filename d filename p 1 2 3 Select which parallel port to use le Erase the entire chip before programming Ir Invertthe resetline s 0 9 hor DOS platform because 486 386 and even 286 computers always make it onto the production floor when the rest of the company upgrades The ISP utility gets binary files off your hard drive and into the 89S The utility supports a few command line options to make it generic For example if your programming interface is attached to LPT2 and FOOBAR BIN is your binary file typing isp exe p 2 c foobar bin should begin the upload operation Table 2 lists the ISP command line options We included the set programming speed s 0 9 option because the rate at which an 89S can be programmed is directly affected by its crystal Al though an 89S running at 20 MHz might program fine at speed 0 the same chip at 1 MHz probably requires an ISP speed setting of 9 We d also like to point out the invert reset line r
151. rumps who hate the aggravations of travelling but considering the positive results of this trip both of us might complain a little less the next time Obviously the big event was Embedded Systems Conference West Like many of the other computer specific trade shows it has evolved considerably over the years Nine years ago ESC W was a modest reflection of the embedded control community Today it s a glitzy spectacle that s equally consistent with the current state of the embedded systems industry used to relish the nomadic trek among the many rows of entrepreneurial startups I d swap war stories with owners and inventors who in those days shared booth duty with everyone else Today Microsoft s booth is larger than most small company parking lots And as far as schlepping the booth to trade shows it s obviously Bill who among the weary exhibit personnel This isn t a complaint It s just a statement of reality about the progress we ve made in this industry The good old days have many fond memories but there s a definite down side to removing technology once we ve come to depend on it certainly wouldn t give up my cellphone or 100 plus processor automobile to be in the good old days again At the same time it would be a hypocritical for me to be overly critical about ESC W when we ve made just as many changes as everyone else over the years Of course our booth isn t the size of a parking lot and you can still find me there Som
152. s bus masters and bus slaves A master Smart battery A Smart battery B Smart battery selector Dual battery system Smart battery charger SMBus Figure 1 The minimum SBS requires a system host smart battery and charger An optional smart battery selector and second battery extend product runtime initiates a message between itself and a slave also attached to the bus by generating a start condition followed by the slave address and a read write bit see Figure 2 Each slave device on the bus has an assigned address Slaves recognize start conditions and monitor slave addresses that traverse the bus A slave recogniz ing its own address on the bus gener ates an acknowledgment bit to signal that the addressed slave is present The master exchanges one or more data bytes and acknowledge bits with the slave and terminates the message with a stop condition or by initiating anew message with a repeated start Table 1 lists the standard SM Bus slave address assignments Within the structure of its messages SM Bus defines the eight command protocols you see in Figure 3 These protocols define the rules that devices connected to the SM Bus must follow and provide a menu of commands for implementing SBS device functions Quick commands send one bit of data to a slave device The value of the Read Write bit 0 or 1 controls the state of a function in the addressed write only slave This command uses
153. s modem Assuming an AT com mand compatible external modem the serial interface is usually an RS 232 connection This connection carries the AT commands from a terminal operator or terminal program to the modem in the form of serial data AT commands determine the modem s next action Both obtaining the serial data and processing AT commands are captured as Use Cases and are shown as separate ellipses in Figure 1 Error correction data com pression and data passing over T elco s lines all identify a different Use Case To model the interaction within the system UML provides Object Sequence and Object Collaboration diagrams In the next section ex plain Object Sequence diagrams in an extended form to incorporate timing UML FOR HIGH LEVEL SUPPORT To capture the main characteristics of real time systems i e timing concurrency and the presence of hard ware want to introduce the diagrams used at this stage of design A System Scope diagram presents the interfaces to the hardware and soft ware It shows the interaction between the actors and system interfaces as well as the interaction of the interfaces with the system s control elements Figure 2 illustrates the external interfaces to my modem using the System Scope diagram namely the serial interface analog phone line Circuit Cellar INK Figure 1 n a Use Case Diagram the system requirements are broken down into individual Use Case groupin
154. s of the IEEE No juggling an unschedulable array of meetings ses sions and keynotes Or maybe it s the chance to see old friends and meet new ones in the rather eclectic audience There are world famous academics fresh faced stu dents VCs venture capitalists on the prowl and grizzled IC vets Despite the ambiance Hot Chips wouldn t have made it ten years if it weren t for worthy content and this year was no exception Besides offer ing a glimpse at the latest and greatest silicon it features some interesting presentations on other hot topics The ultimate attraction of course is the chips themselves If the day comes when there aren t any new hot chips there won t be any Hot Chips conference Fortunately silicon con tinues to march on and there s no shortage of stuff to write about ARCHITECTURE WARS Keeping pace with Moore s Law is no trivial task For some time it has seemed that computer architects have had trouble coming up with any break throughs or radical changes in computer organization that have really paid off Instead the continuing trend is an attempt to wring the last bit of perfor mance out of the traditional solutions by brute force i e throwing transistors at the problem It would be easy to contend that architecture is dead were it not for the fact that the name of the game is performance at any price no matter how little the gain no matter how high the price The bag of
155. set input The 705 706 and 813L feature a watchdog timer output that goes low if the watchdog input is not triggered within 1 6 s The 813L has the same pinout and functions as the 705 but has an active high reset output The 707 and 708 have active high and active low reset outputs instead of a watchdog function 10 Issue 101 December 1998 Circuit Cellar INK NEW nae NEWS 68338 COMPUTER MODULE The Persistor CF1is a modular microcomputer system using CompactFlash CF technology to extend the range of remote and portable data acquisition The 1 4 x 2 5 x 0 5 unit gives instant access to all microcomputer resources including 68020 processing power a DOS like OS and up to 48 MB of secure transportable CF storage The CF1 features an integral PicoDOS OS running on a 16 M Hz Motorola 68C K338 coupled with 1 MB program flash and 256 KB battery backed SRAM It has an onboard 3 3 V linear regulator power management circuitry that reduces current drain to below 5 uA real time clock dual RS 232 driver QSPI interface 15 counter timers and full 16 bit bus expansion The developer s CD offers projects with commented source code and HTML descriptions The PicoLog Recipe Card a 3 x5 circuit board turns the Persistor into an eight channel 12 bit analog recorder that samples at variable rates up to 1 KHz and stores to CF files PicoDOS uses DOS prompts and commands runs batch and execut
156. sk or in multiboot configurations where Linux is one of the OSs that can be booted In the multiboot environment a boot loaderpromptsfor the O S to load Choices can include booting DOS Windows 95 W indows NT and others besides Linux Installation of Linux to a hard disk is the normal procedure and since it s covered by the documentation that comes with most Linux distributions won t discuss it here However do want to tell you how to deal with booting Linux in an embed ded environment where you may boot Linux from flash memory or floppy disk To boot Linux you have to load the Linux kernel thatyou have builtinto memory and start running it Typically you do this by using a boot loader like LiLo Linux Loader LiLo has evolved to be very flexible and configurable It is installed in the boot block of a boot disk W hen LiLo boots it consults a table to find out what images are available for booting These images can be Linux ker nel images DO S or W indows boot parti tions and other Intel based operating systems such as OS 2 or QNX which use the normal boot block method of booting Linux must be running to install and configure the LiLo boot loader We can build a configuration LiLo file which tells Listing 2 There are several steps to creating a RAM disk image suitable for use as a root partition for Linux One handy feature in Linux is the loopback device This device can be used to map a file to a
157. ster part the 2343 has five general purpose I O pins when using the internal RC os cillator An external crystal provides an accurate timebase but the 2343 s internal RC oscillator is handy when combination of goes here and 128 bytes of high endurance nonvolatile Data register Port B reg Port B EFTE Wy Port B drivers Data dir PBO PB4 Figure 1 While every micro has its own personality the AVR devices contain a standard and special function blocks great accuracy iS unnecessary and extra I O is needed Since the address path of these micros is 16 bits wide no bank switch ing is necessary All code and data are available through direct and or indirect addressing Although these small parts have a thousand words of code space the entire code written is up Listing 1 The beginning BASIC code demonstrates how the parallel ports can be searched for the program mer hardware amp H3BC REM REM Ipt 2 amp H3 8 DATA BITS X X X IRQ4EN DLPT CLPT XXX01011 lpt 1 0 2 SLPT 1 REM BUSY ACK P FOR x 1 T0 3 0 pt x CLPT I I NP Ipt x SLPT A 0 CLPT I I t x SLPT A nd LPT x 1 ind the Progr SCKHI amp H2 LO 0 RESET NT Programm Insert chip to be pr INKEY IF I THE T lpt RESETHI VCCHI T Placing chip into RE pt VCCHI D 1000 1
158. sting 3 This routine calls other routines written in C and as sembly code There s little point in developing a complicated assembly language sequence to print out a title when a simple C call can do the job Because the message to the display device is limited by a slow transmis sion rate over the serial line assembly code doesn t offer a speed advantage N ote the two entry points for each assembl y code function The entry point with the leading underscore makes it easy to call the subroutine from C The entry point without the underscore is better for calling the routine directly from assembly code developed a coding practice that provides both entry points whether they re needed or not This technique makes code maintainability easier and avoids the common error of forgetting to code the entry point you end up using in the final program HIDDEN ERRORS ALREADY Although it seems unlikely in the 20 or so lines of code developed there s already one possible error source that could crash the processor An error can occur whenever an algorithm is developed with one routine calling and then returning from another routine But the problem is far less obvious because assembly and C sub nonobvious purpose Listing 4 shows two pos sible solutions N o register values are destroyed in Reset DeviceV2 where an absolute ad dressing mode instruction is used to set the Control register This mode of operation gen
159. t a swept or chirp style sampling method For those brave enough to use it the analysis math for nonuniformly spaced sampling has already been done elsewhere A better solution known as a time slip or incre mental delay method is older than some hills and makes few demands on the hardware Paddy McKee Paddy keetech demon co uk To address Darrell s point first in the section Real World Considerations discussed choosing a sample rate Let s choose 9 kHz The sum of the A D rates is 19 kHz which is close to the conventional example of 20 kHz p 34 included that example to show that relaxed input filtering can be used with a conventional rate Secondly in Figure 5 there are nonmultiplexed inputs either two ADCs or two sample holds And Figure 4 would require a very fast ADC if nonrepetitive signals were to be measured But in the Implementation section stated that the method is suitable for systems with constant or repetitive signals p 33 I m aware of the 1 fsa 1 fsb obstacle and why Figure 4 is limited That s why included Figure 5 The 1 fsa 1 fsb consideration wasn t mentioned because every detail can t be covered in one article Nowhere in my article is a method described for adding the spectra In the Implementation section state Since the sample rate affects the characteristics of the FFT the spectrum comparison routine won t be completely trivial p 33 Also pointed ou
160. t of digitizing this signal It looks messy but when you do the analysis in Figure 6b iii and 6b iv several important things stand out The perception of the tone in Figure 6b iii doesn t stop abruptly but gradu ally turns into a more random signal You can still see traces of the tone well beyond the point at which the undithered system quit and it looks a lot more like the original sine wave Finally the residual in Figure 6b iv although it has a higher amplitude than the one in Figure 6a doesn t vary in amount or character So it s less objectionable to listen to and most people get used to it and can ignore it Of course the dither signal be comes noise at the ADC s output So its characteristics must be chosen so that its effects are relatively benign Dither can also be applied in places other than ADCs In fact you want to Circuit Cellar INK Issue 101 December 1998 71 72 Issue 101 December 1998 consider dithering whenever the reso lution of a digital signal is reduced This reduction can occur whenever arith metic is performed on a digital signal For example multiplying a 16 bit digital audio sample by a 16 bit volume control value creates a result with 31 bits of precision If you truncate this to 16 bits again you re doing a form of requantization and it may be appro priate to add dither to the product first DITHER PARAMETERS There are many ways to create ran dom or
161. t on their feet react quickly and cater to customer demands ISP makes those three goals just a little easier to reach l Craig Pataky is a systems engineer with over nine years of experience ranging from simple embedded pro gramming to OS design You may reach him at craig ogical co com Bill Maggs is an electrical engineer with over eight years of enbedded design experience His designs range from low power handheld devices to fixed station monitoring equipment You may reach him at www logic fire com SOFTWARE Source code for this article is avail able via the Circuit Cellar web site SOURCES 89Sxx microcontrollers Atmel Corp 408 441 0311 Fax 408 436 4200 www atmel com PIC 16C56 Microchip Technology Inc 602 786 7200 Fax 602 899 9210 www microchip com BASIC Stamp Parallax Inc 888 512 1024 916 624 8333 Fax 916 624 8003 www parallaxinc com Circuit Cellar INK Issue 101 December 1998 A Minimalist Multitasking Executive A multitasking execu tive might seem like a nice enhancement but the costs are prohibitive right Well maybe they don t have to be With exec even simple embedded programs can be written as multiple tasks 20 Issue 101 December 1998 FEATURE ARTICLE Richard Man amp Christina Willrich typical embedded program reads data from input devices ADC keypad serial port etc and after some processing gener
162. t style2 100 short int style6 10 1 2 3 char style5 malloc 200 Funcl stylel style2 3 printf Hello World return style5 volatile ensures that the mem ory location is accessed at each step volatile long int pt volatile long int 0xA0000 long int sum 0 for count 0 count lt max count sum pt Sum sum gt gt 3 Hint Use assembly language to access hardware MORE BUMPS IN THE DARK I ve covered many things that must be considered when cross linking C and assembly programs But you can be haunted by many things that are compiler and processor dependent Many programmers use the com piler s S option as a starting point for style4 4 producing custom code when generat ing assembly code from C This method has many possible trade offs One optimization of the SDS com piler is to use RTD rather than RTS RTD pulls the return address and a specified number of pushed parameters from the stack The number of instructions to be stored in program ROM is re duced because the stack is adjusted within one commonly called routine rather than during each calling routine Other optimizations see Table 2 can hinder future use of the C code assembler listing as a starting point for optimized code Dead code removal may remove values you want before you ever use them in a customized way One advantage of frame pointers is that the position of the incoming par
163. t why direct addition or comparison of spectral lines won t work As for the Z diagram its purpose is to illustrate frequency foldback The diagram was novel to me because had been unfamiliar with it Certainly the chirp to Z transform isn t for the faint of heart but I m not trying to reinvent FFT and all subsequent work In the More Samples section p 34 admitted that the math corrections aren t trivial and that work is progressing slowly Of course when it comes to ideas it s easy to find reasons why something won t work It s more rewarding though often more difficult to find a way to make it work that s the essence of being an entrepreneur Gerard Fonte ATEMENT REQUIRED BY THE ACT OF AUGUST 12 1970 TITLE 39 UNITED STATES CODE SHOWING THE OWNERSHIP MANAGEMENT AND CIRCULATION OF CIRCUIT CELLAR INK THE COMPUTER APPLICATIONS JOURNAI published monthly at 4 Park Street Vernon CT 06066 Annual subscription price is 21 95 The names and addresses of the Publisher Editorial Director and Editor in Chief are Publisher Steven Ciarcia 4 Park Street Vernon CT 06066 Editorial Director Steven Ciarcia 4 Park Street Vernon CT 06066 Editor in Chief Steven Ciarcia 4 Park Street Vernon CT 06066 The owner is Circuit Cellar Inc Vernon CT 06066 The names and addresses of stockholders holding one percent or more of the total amount of stock are Steven Ciarcia 4 Park Street Vernon CT 06066 T
164. tem This may be done at an architectural level by the system engineers and later elaborated on by the software engineers as a part of the detailed design Referring to one of the Use Cases from Figure 1 AT command processing one of the possible scenarios is depicted in Figure 4 The directed lines between the actor and the objects denote a function call message or event Note that the timing information associated with a given message identifies the propagation delay or latency In this example it takes the AT N5 command about 608 us at 115 2 kbps to travel from the terminal to the AT command processor Once the message arrives it may take the AT command processor 200 ms to process the request Both of these can be specified by the system engineer and added to the OSD The vertical axis in Figure 4 repre sents time moving from top to bottom So we can specify the round trip time for replying to an AT command a combination of many sequences as a vertical line with 1 s duration Another way to study the interaction in the system is through UML Collabo 28 Issue 101 December 1998 ration diagrams A reference like UML Distilled Applying the Standard Ob ject Modeling Language provides more information DESIGNING THE DETAILS Embedded systems present the problem of where to draw the line between hardware and software areas of responsibility From a distance we can view the solution to the detailed design prob
165. the command code to the slave device which enables it to tell the slave what information it requires The master then without generating a stop condition sends a new message to the slave reading one or two bytes of data As with Write Byte Word the 8 bit data byte holds a value of 0 255 and the 16 bit data word holds a value of 0 65 535 The SM Bus host device can use this command to request battery pack temperature information from a smart battery The command code byte tells the slave that the data to transmit should be the battery pack temperature Process Call islikeaWrite Word followed by a Read Word but it uses a repeated start and only a single com mand code for the entire sequence Here the master writes the command code plus two data bytes 16 bits low byte first to the slave device This step enables the master to issue a command to the slave and provide two bytes of data that the slave can use for internal computations Then the master without generating a stop condition sends a new message to the cess Call is used in more computa tionally intensive situations Block Write sends a series of data bytes to a slave receiver device The command code tells the slave how to interpret the remaining bytes in the message The byte count with a valid range of 1 32 tells the slave how many data bytes should follow Block Read is used to read a series of data bytes from a slave transmitter It also involves a tw
166. tmel 89Sxx series of 8051 compatible ISP microcontrollers with integrated flash and E We ve been designing with this family for the last year and because the device is a mere 10 in quantity we re building it into all of our new products The Atmel ISP family comprises the 89S8252 and the 89S53 The 89S 8252 has 8 KB ISP code memory and 2 KB ISP E data memory whereas the 89S53 has 12 KB ISP code memory but no ISP E data memory According to Atmel arm yourself with the 89S series and software modifications are as simple as the wave of a wand Truly we live in times of reprogrammable bliss WELL NOT QUITE Of course any significant innovation is useless if it you can t take advantage Issue 101 December 1998 15 of it This is the one area where Atmel came up short Although the ISP nature of the 89Sxx series promises Target Powered Dongle u10 74HC125 sist ZIRS R3 R4 Li to revolutionize the design cycle Atmel didn t provide any utilities to get our bina ries into the chip Their documentation was cryptic at best The data sheets are concise about 18 k2 Oke appropriate ISP pins The parallel port was the obvious choice As mentioned in Beyond We The Box With Windows 95 WLA 74HC125 El f INK 74 even the most basic PEPEPEPBPRR EP a S RESET fa foo Y1B 74HC125 E fo co
167. to help model system details it fails to provide a convenient way to map the application software to the underlying hardware Going back to Figure 5 sandwiching the software architecture layer between the objects and the hardware lets us map the former to the underlying hardware So by introducing the concurrency and storage diagrams you can map the RTOS tasks and the data storage objects on to the hardware entities all without compromising the boundary that divides the two layers One advantage of layering is that you can cleanly differentiate between the system hardware and software components As well objects are mapped to the software architecture layer instead of directly to the system Object architecture Interface Control Entity Software J the operations of a class evolve they can be directly mapped into source code in the OO language of choice Typically C and to a lesser extent Java are used in embedded systems The CPP and H files in List ing 1 were generated using an Circuit Cellar INK architecture architecture Architecture Figure 5 At each level in the embedded system design process designers must consider the needs of each individual layer as well as how it interacts with the next level Listing 1 These C header files contain the class definition source code for the AT Command Pro cessor andAsyncData_I 0 classes ifndef _ ASYNCDATA_IO_H define _ _ASYNCDATA_IO_H
168. transfer the data to other applications A user can automate data collection and analysis using the software drivers supplied The auto ranging multi meter features simultaneous display of multiple pa rameters such as true RMS or DC voltage decibel gain and frequency measurements Software drivers are supplied for users who want to program Windows NT LabVIEW Excel and Visual Basic applications The direct computer hookup provides the ability to annotate save and print traces on ordi nary or networked printers in black and white or color ADC 216 comes ready to use with software cables and power supply at 799 A 12 bit version the ADC 212 is available at 499 Saelig Company 716 425 3753 Fax 716 425 3835 www saelig com Circuit Cellar INK Issue 101 December 1998 11 MAYA 10 been E NEW ECONOMICAL LOAD AND FORCE SYSTEM TeKscan has announced a simple load measurement system that uses single element sensors The ELF system uses a serial interface Windows software and innovative electronics to provide an economical solution to measure ment problems Applications include variable force control for joysticks occupant detection weight measurement and distribution and fill rates and pressures The ELF system is durable accurate and simple to use The system allows for non intrusive measurement and the sensors are small enough to allow for precise placement The thin sensors 0 005 0 127
169. ult to detect small blood splatters and tissue remains around a corpse during daylight hours This new hardware illuminates the crime scene with rapid flashes of light causing the blood splashes to fluoresce But the fluorescence can t be seen above normal daylight reflection so the detective wears glasses with lenses that darken By making the darkening rate different than the timing of the flashes the tissue samples seem to flicker on and off like Christmas lights l II assume there are five hardware registers necessary to control the Generalized Locator of Blood GLOB device These registers shown in Table 3 were deliberately chosen to have size and offset characteristics that could cause problems when ac cessed from a C program Listing 1 The main c code contains a call to an assembly language routine Ca 1 1ASM anda C utility called from assembly code include lt stdio h gt void main void void CallAsm void void ShowTitle void void main void CallAsm id ShowTitle void printf ACME GLOB V1 n Switch to assembly code Listing 2 The stack and various other parameters are initialized before program control is transferred to C from within the init s assembly code EXPORT START IMPORT _main IMPORT STKTOP ResetInit START MOVEA L STKTOP SP SR ResetInit SR _main RAP 15 DC W RETURN_TO_KERNEL Call Establish stack needed for C and assemb
170. uses exec can be used to implement subsumption architec ture which is a powerful program ming paradigm particularly suitable for programming autonomous robots If you re interested we recommend checking out Mobile Robots Inspira tion to Implementation 1 for more detailed information on subsumption programming ENHANCEMENTS In summary exec is a small simple to use simple to port and yet Circuit Cellar INK useful multitasking executive Its resource usage is modest taking only about 700 bytes on an HC11 With this executive even simple embedded programs can be written as multiple tasks gaining you the ben efit of having a preemptive executive Naturally there are plenty of pos sible enhancements such as adding the watchdog timer function that comes with most microcontrollers to the system As well you might choose to modify the system so that error conditions can be reported via your system s output mechanisms serial port LCD or even just a blink ing LED Or why not modify the system so that it prints out the maximum stack usage for each task You can even add a name field to the task control block so that diagnostics can be printed with the task s name kl Richard Man and Christina Willrich are the owners of ImageCraft a com pany which specializes in low cost professional ANSI C tools for micro controllers plus HC12 hardware and BDM debug Pods You may contact them via
171. veau PU 52 CIRCUIT CELLAR INK DECEMBER 1998 Real_Time PC Ingo Cyliax Imbedded RI Linux Part 2 Working with Flash Memory Once you decide that Linux might be the right OS for your embedded application where do you go next Ingo has the answers as he reduces the Linux kernel and even shows how to boot it from Hash memory or floppy disk hen introduced Linux last month covered the initial development of Linux as a conventional operating system for desktop and server systems But because Linux tries to satisfy the needs of many it tends to be very modular and flexible Therefore it can also to be pressed into service as an embedded OS for many 32 bit processors W ith such possibilities at hand wanted to explain how to embed Linux Formany embedded applications we want a small streamlined OS Desktop and server installations typi cally include relatively large memory configurations since you don tusually know what applications and pro grams you mightend up running on it Today s feature laden desktop applications tend to be bloated for the amount of work they do As we re frequently told memory is cheap W ell although memory might be cheap in the embedded systems co debug loadlin irectory for A itrd Loexec world every dollar spenton memory and other frivolous resources comes out of the profit margin O ur goal make systems as lean and mean as possible withoutinvest ing a l
172. www imagecraft com SOFTWARE Complete source code for exec is available via the Circuit Cellar and ImageCraft web sites REFERENCE 1 J L Jones and A M Flynn Mobile Robots Inspiration to Implementation A K Peters Natick MA 1993 SOURCES 68HC11 microcontroller Motorola MCU Information Line 512 328 2268 Fax 512 891 4465 www mcu motsps com ICC11 HC11 C complier ImageC raft 650 493 9326 650 493 9329 www imagecraft com Issue 101 December 1998 FEATURE ARTICLE Irv Badr Object Oriented Design of Real Time Systems A Multidisciplinary Challenge During the design stage the system hardware and soft ware engineers all have their own issues and development tools Irv presents a way to balance and coordinate the efforts so we can all speak a common language at last Issue 101 December 1998 esigning real time embedded systems involves a multidisciplinary team of engineers System engineers get the process started and because they are primarily concerned with the overall architecture they often make trade offs that influence the hardware and software composition Hardware engineers design circuitry that fulfills the system requirements as determined by the system engineers And because the majority of the sys tem functionality lies in the software the software engineers have the larg est design and implementation task Photo 1 There s m
173. ycle was completed as a busy ready handshake Warnings are given not to clock in any additional commands while in an internal pro gramming cycle There s also a discrepancy in the SCK times between the app note and the datasheet The note says one crystal clock cycle low and four crystal clock cycles high but the datasheet says two and two Since my BASIC program can t run anywhere near that fast I m not worried about it But there are some delays i e 4 ms need to take into account BASIC has a sound command which is measured in timer 12 ms tics use the minimum beep to make sure that a fast PC can t execute the write faster than 12 ms And last think the timing diagram is a bit misleading in both documents The MISO output is clocked on the falling edge and therefore should be read before dropping the clock If read MISO output after the clock falls as implied by the timing diagram find myself a bit behind FLIGHT SIMULATOR For those of you who can remember DOS you may also remember that some form of BASIC always came with DOS One of my friends recently complained to me because his brand new PC had Windows 98 installed and there was no DOS or BASIC available don t know where I d be without some BASIC on my machine Listing 1 is the beginning of a BASIC program using the PC s parallel port to control the AVR programmer This code searched the three ports to find the attached programmer L
174. ylel arrays are made by allo cating space on the stack These auto matic arrays don t have a fixed starting address and only exist while the func tion containing them exists If the function exits the space is deallocated and the array and its values vanish Static sty1e2 and global style3 arrays exist independently of the stack and are located in aRAM section set aside for all static and global variables These arrays have a fixed starting address once the program is loaded into memory Constant arrays sty1le4 are found in a memory section set aside for constant values Be careful if you initialize a string variable sty1e4 and then change its contents Some compilers use the same memory for style4 andthe Hello World array used as a printf parameter Arrays style5 generated via calls to C memory allocation functions like malloc or the C new operator exist within a memory section called the heap Provided the memory alloca tion for the array isn t freed the start ing address is fixed even though it s a function when malloc is performed Initialization of variables including arrays style6 occurs many ways Downloading code using S records generated by the SDS compiler places the values into the array which causes problems if the code is rerun without being downloaded a second time 40 Issue 101 December 1998 A better approach available from the SDS compiler is to store these
175. z x at higher sample 6a iii which is perceived as noise Desired rate ind Image at i al e i Y ou can see that the amplitude of aaa Images removed by produce by asi interpolating filter D S Modulator the waveform decreases in steps and that the waveform harmonic struc ture changes through each step The noise is modulated by the tone and Le both the amount and the character of the noise change over time Response of itched itor filt As demonstrated in Part 2 with merine am ec eee PWMs and this month with delta sigma converters you can exploit the ability Pi gt of a binary signal to represent levels M X Frequency 4 Original sample rate New sample rate falling between its two values by Nyquist limit Nyquist limit averaging a waveform over time ither isaw f using th m m as B ISa Way ae alee Figure 5a The DAC uses a digital delta sigma modulator to create an oversampled one bit datastream which is effect in reverse By addi ngan ANC Ole then filtered in the analog domain b The various filtering stages deal with the problems of images sin x related random signal noise to the correction and quantization noise signal being digitized the pattern of output codes from a quantizer can be averaged to produce levels that are effectively between the nominal deci sion points of the converter Figure 6b shows the fading tone again but with 1 6 quants of peak to peak dither added Figure 6b ii shows the resul

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