lab2 - Cristinel Ababei
Contents
1. IIRValue amp 0x07 check bit 1 3 interrupt identification Which shifts right with one bit HR Value and then AND s it with 0x07 This effectively zooms in onto the field formed by bits index 1 3 from the original LPC_UARTO0 gt IIR bits which are now in the position bits index 0 2 of IR Value variable Going on we find an if instruction with several branches if IIRValue IIR RIS Receive Line Status fuses else if IIRValue IIR_RDA Receive Data Available ees else if IIRValue IIR CTI Character timeout indicator 8 ers else if IIRValue IIR_THRE THRE transmit holding register empty ans See in Table 276 on page 303 in the User Manual what is the meaning of the three bits 1 3 from the original IR register 011 1 Receive Line Status RLS 010 2a Receive Data Available RDA 110 2b Character Time out Indicator CTI 001 3 THRE Interrupt For each of these situations something else is done inside the corresponding branch of the if instruction above In other words we first identify the interrupt and for each ID we do something else If none of the expected IDs is found we do nothing Please take your time now to explain what s done in each of these cases Read pages 303 304 in the User Manual for this This is very important in order to understand the overall operation of the example of this lab 4 Lab Assignment 12. uarttest c contains a small test program utilizing the UART driver system_LPC17xx c Cortex M3 Device Peripheral Access Layer Source File startup_LPC17xx s CMSIS Cortex M3 Core Device Startup File Abstract txt Describes what the uarttest c program does Change include Ipc17xx h to include lt Ipc17xx h gt This is done in order to use the latest Keil s release of the header file normally located in C Keil ARM INC NXP directory Step 3 Make sure the uVision4 Target setting is FLASH Then build the project by rebuilding all target files Download to the microcontroller and confirm that download is ok Step 4 Establish a Terminal connection Method 1 If your Windows is XP or older you can use HyperTerminal Start HyperTerminal by clicking Start gt All Programs gt Accessories gt Communications gt HyperTerminal Connect HyperTerminal to the serial port that is connected to the COMO port of the evaluation board for example For the HyperTerminal settings you should use COM1 double check that it the host s serial port is indeed COM lin your case you can do that by Start gt Control Panel gt System gt Hardware gt Device Manager and click on Ports COM amp LPT if in your case it s a different port number then use that for example in my case as I use the USB to serial adapter with my laptop the port is COM14 baud rate 57600 8 data bits no parity 1 stop bit and no flow control Method
3. See pages 298 and 318 of the LPC17xx User s Manual 1 See also page 27 of the Datasheet 2 UARTO and UARTI of the microcontroller are connected on the MCB1700 board to the ST3232C IC6 which converts the logic signals to RS 232 voltage levels This connection is realized from pins P0 2 TXD0 AD0 7 and P0 3 RXD0 AD0 6 and P2 0 PWM1 1 TXD1 and P2 1 PWM1 2 RXD1 of the microcontroller to the pins 10 9 11 and 12 ST3232C chip The ST3232C chip drives the two COMO and COM represented by the two female DB9 connectors Note if you use an Embest LPC1700 board then note that these two connectors are male DB9 connectors To see these connections take a look on pages 1 and 3 of the schematic diagram of the board 3 included also in the downloadable files of this lab 2 For more details on UART and RS 232 please read references 1 6 In this lab we will explore serial communication between the target LPC1768 UART and a serial communication port of the host PC 3 EXAMPLE 1 Microcontroller echoes back the characters sent by host computer a Experiment In the first example of this lab well use an example project that comes with the LPC1700 code bundle The LPC1700 Code Bundle is a free software package from NXP that demonstrates the use of the built in peripherals on the NXP LPC17xx series of microcontrollers The example software includes a common library peripheral APIs and test modules for the APIs Download L
4. not graded and should not be discussed in the lab report Use a Debug session to step through the execution of this program The scope is for you to better understand its operation See lab 1 for how to use run a debug session See also documentation of the code bundle from NXP 7 2 Answer the question Why did we need to remove the ISP and RST jumpers in Example 1 3 Describe in less than a page typed font size 11 single line spacing all instructions inside the function void UARTO_IRQHandler void for each of the branches of the main if instruction Include this in your lab report 4 Modify Example such that the characters typed on the host s keyboard are also displayed on the LCD display on the board Hint re use code from Blinky2 example of lab 1 5 Credits and references 1 LPC17xx user s manual http www nxp com documents user_manual UM10360 pdf part of lab 1 files 2 NXP LPC17xx Datasheet http www nxp com documents data_sheet LPC1769_68 67 66 65 64 63 pdf part of lab 1 files 3 Schematic Diagram of the MCB1700 board http www keil com mcb1700 mcb1700 schematics pdf part of lab 2 files 4 MCB1700 Serial Ports http www keil com support man docs mcb1700 mcb1700_to_serial htm 5 UART entry on Wikipedia click also on the references therein for RS 232 http en wikipedia org wiki Universal_asynchronous_receiver transmitter 6 Jonathan W Valvano Embedded Systems Introduction to Arm Cortex M3 Mi
5. a multi threaded system threads are normally cooperating to perform an overall task Consequently we ll develop ways for threads to communicate e g FIFOs and synchronize with each other A process is also defined as the action of software as it executes Processes do not necessarily cooperate towards a common shared goal Threads share access to I O devices system resources and global variables while processes have separate global variables and system resources Processes do not share I O devices To arm disarm a device peripheral means to enable shut off the source of interrupts Each potential interrupting trigger has a separate arm bit One arms disarms a trigger if one is is not interested in interrupts from this source To enable disable means to allow interrupts at this time postponing interrupts until a later time On the ARM Coretx M3 processor there is one interrupt enable bit for the entire interrupt system In particular to disable interrupts we set the interrupt mask bit I in PRIMASK register Note An interrupt is one of five mechanisms to synchronize a microcontroller with an I O device The other mechanisms are blind cycle busy wait periodic polling and direct memory access With an input device the hardware will request an interrupt when input device has new data The software interrupt service will read from the input device and save in global RAM With an output device the hardware will request an
6. buffer UARTOBuffer This is done only if there are characters in the buffer the total buffer size is 40 characters which have been received so far from the host PC The number of characters received so far and not yet echoed back is stored and updated in UARTOCount e Once the transmission of all characters from the buffer is done reset the counter UARTOCount e Enable Receiver Buffer Register RBR This is achieved by setting to 1 the LSB of IER which in turn is achieved using the mask IER_RBR c Source code discussion Please take your time now to thoroughly browse the source code in files uart c and uarttest c files Open and read other files as necessary to track the declarations and descriptions of variables and functions For example in uarttest c we see A function call SystemClockUpdate This is described in source file system_LPC17xx c which we locate in the Project panel of the uVision4 IDE Click on the name of this file to open and search inside it the description of SystemClockUpdate This function is declared in header file system_LPC17xx h Open these files and try to understand how this function is implemented what each of the source code lines do A function call UARTInit 0 57600 This function is described in source file uart c The declaration of this function is done inside header file uart h Open these files and read the whole code try to understand each line of the code An instruction LPC_U
7. interrupt when the output device is idle The software interrupt service will get data from a global structure and write it to the device Sometimes we configure the hardware timer to request interrupts on a periodic basis The software interrupt service will perform a special function for example a data acquisition system needs to read the ADC at a regular rate On the ARM Cortex M3 processor exceptions include resets software interrupts and hardware interrupts Each exception has an associated 32 bit vector that points to the memory location where the ISR that handles the exception is located Vectors are stored in ROM at the beginning of the memory Here is an example of a few vectors as defined inside startup _LPC17xx s __ Vectors DCD initial p Top of Stack DCD Reset Handler Reset Handler DCD NMI Handler NMI Handler DCD HardFault Handler Hard Fault Handler External Interrupts DCD WDT_ IRQHandler 16 Watchdog Timer DCD TIMERO IRQHandler ATs Timer DCD UARTO_IRQHandler 21 UARTO ROM location 0x00000000 has the initial stack pointer and location 0x00000004 contains the initial program counter PC which is called the reset vector It points to a function called reset handler which is the first thing executed following reset Interrupts on the Cortex M3 are controlled by the Nested Vector Interrupt Controller NVIC To activate an interrupt source we need to set its priority and enable that source i
8. optional do not do it on computers in the lab On your own computer only download and install NXP s FlashMagic tool from here http www flashmagictool com Then follow the steps that describe how to use this tool as presented in the last part of the UART documentation for the code bundle http ics nxp com literature presentations microcontrollers pdt code bundle lpcl 7xx keil uart pdf included in the downloadable archive of files for this lab Note With this approach one does not need the ULINK2 programmer debugger b Brief program description Looking at the main function inside the uarttest c file we can see the following main actions UARTO and UART are initialized UARTInit 0 57600 baud rate setting UARTInit 1 57600 baud rate setting A while loop which executes indefinitely either for UARTO or for UART1 The instructions executed inside this loop let s assume the UARTO are e Disable Receiver Buffer Register RBR which contains the next received character to be read This is achieved by setting all bits of the Interrupt Enable Register IER to 0 except bits THRE and RLS In this way the LSB i e bit index 0 out of 32 bits of IER register is set to 0 The role of this bit as explained in the LPC17xx User s Manual 1 on page 302 when set to 0 is to disable the Receive Data Available interrupt for UARTO e Send back to the host the characters from the
9. 2 If your Windows is 7 or newer you first must make sure you download and or install a serial connection interface because HyperTerminal is not part of Windows 7 or later On the machines in the lab you can use Putty http www putty org Start gt All Programs gt Putty gt Putty Then select Connection Serial and type COM1 or whatever is in your case find what it is as described in Method 1 baud rate 57600 8 data bits no parity I stop bit and no flow control Click on Session and choose the type of connection as Serial Save the session for example as lab2 Finally click on Open you should get HyperTerminal like window Method 3 You can use other programs such as TeraTerm http logmett com index php products teraterm html or HyperSerialPort http www hyperserialport com index html or RealTerm http realterm sourceforge net or CoolTerm http freeware the meiers org etc Step 5 Type some text It should appear in the HyperTerminal window This is the result of First what you type is sent to the microcontroller via the serial port that uses a UART Second the MCU receives that via its own UART and echoes sends back the typed characters using the same UART The host PC receives the echoed characters that are displayed in the HyperTerminal Disconnect the serial cable from COMO and connect it to COM1 port on the MCB1700 board The behavior of project should be the same Step 6
10. A commonly used device for encoding and decoding such asynchronous bit streams is a Universal Asynchronous Receiver Transmitter UART UART is a circuit that sends parallel data through a serial line UARTs are frequently used in conjunction with the RS 232 standard or specification which specifies the electrical mechanical functional and procedural characteristics of two data communication equipment A UART includes a transmitter and a receiver The transmitter is essentially a special shift register that loads data in parallel and then shifts it out bit by bit at a specific rate The receiver on the other hand shifts in data bit by bit and reassembles the data The serial line is 1 when it is idle The transmission starts with a start bit which is 0 followed by data bits and an optional parity bit and ends with stop bits which are 1 The number of data bits can be 6 7 or 8 The optional parity bit is used for error detection For odd parity it is set to 0 when the data bits have an odd number of 1 s For even parity it is set to 0 when the data bits have an even number of 1 s The number of stop bits can be 1 1 5 or 2 The transmission with 8 data bits no parity and 1 stop bit is shown in Fig 2 note that the LSB of the data word is transmitted first idle yo Start bit stop bit Figure 2 Transmission of a byte 1 No clock information is conveyed through the serial line Before the t
11. ARTO gt IER IER_THRE IER RLS Disable RBR Based on what s been studied in lab 1 you should know already that LPC_UARTI is an address of a memory location the UARTO peripheral is mapped to this memory location Starting with this memory location several consecutive memory locations represent registers associated with this peripheral device called UARTO All 14 such registers or memory locations are listed on page 300 of the User Manual Utilizing this peripheral is done through reading writing into these registers according to their meaning and rules described in the manual For example one of the 14 registers associated with UARTO is Interrupt Enable Register IER Form a C programming perspective LPC_UARTI is declared inside header file LPC17xx h define LPC_UARTO LPC_UART_TypeDef LPC_UARTO BASE Which also declares what LPC_UARTO BASE as define LPC _UARTO BASE LPC_APBO BASE 0x0C000 Where LPC_APBO_BASE is declared at its turn in the same file define LPC APBO BASE 0x40000000UL This effectively makes LPC_UARTO_BASE to have value 0x4000C000 which not surprisingly coincides with what is reported on page 14 of the LPC17xx User s Manual 5 Furthermore the Interrupt Enable Register IER contains individual interrupt enable bits for the 7 potential UART interrupts The IER register for UARTO is mapped or associated with to memory address 0x4000C004 as se
12. Lab 2 Using UART EE 379 Embedded Systems and Applications Electrical Engineering Department University at Buffalo Last update Cristinel Ababei January 2013 1 Objective The objective of this lab is to utilize the Universal Asynchronous Receiver Transmitter UART to connect the MCB1700 board to the host computer Also we introduce the concept of interrupts briefly In the example project we send characters to the microcontroller unit MCU of the board by pressing keys on the keyboard These characters are sent back i e echoed looped back to the host computer by the MCU and are displayed in a hyperterminal window 2 UART The most basic method for communication with an embedded processor is asynchronous serial It is implemented over a symmetric pair of wires connecting two devices referred as host and target here though these terms are arbitrary Whenever the host has data to send to the target it does so by sending an encoded bit stream over its transmit TX wire This data is received by the target over its receive RX wire The communication is similar in the opposite direction This simple arrangement is illustrated in Fig 1 This mode of communications is called asynchronous because the host and target share no time reference no clock signal Instead temporal properties are encoded in the bit stream by the transmitter and must be decoded by the receiver TX Target RX Figure 1 Basic serial communication
13. PC1700 Code Bundle from 7 http ics nxp com support software code bundle lpc 17xx keil and save it in your own work directory Save it with the plan to keep it as we ll revisit some other example in the future Unzip it to get the keil_examples folder created with several examples therein Take a minute and read keil_example readme txt now Launch Keil uVision4 and then open the project UART from among the example just downloaded The UART project is a simple program for the NXP LPC17xx microcontrollers using Keil s MCB1700 evaluation board When sending some characters from a terminal program on the PC at a speed of 57600 Baud to the LPC17xx UARTO or UARTI the LPC17xx will echo those same characters back to the terminal program Step 1 Connect the board ULINK2 and the host computer as shown in Fig 4 Ask the TA for the COMO 1 to Serial Port cable Note Remove the RST and ISP jumpers on the MCB1700 board USB USB Ports 7 Serial Port Note instead of ULINK2 you can also use ULINK ME Figure 4 Hardware setup Remove the RST and ISP jumpers Please keep the jumpers safe and place them back when you are done with this lab Note Ifyou are doing this lab using a laptop which does not have a serial port you can use a USB Serial Converter I got mine for about 12 from Amazon 8 and it works great Step 2 Familiarize yourself with the following files uart c contains the UARTO UARTI handlers driver functions
14. crocontrollers 2012 Chapters 8 9 Pong P Chu FPGA Prototyping by VHDL Examples Xilinx Spartan 3 Version Wiley 2008 Chapter 7 Lab manual of course http homes soic indiana edu geobrown c335 Chapter 5 EE 472 Course Note Pack Univ of Washington 2009 http abstract cs washington edu shwetak classes ee472 notes 472 note _pack pdf Chapter 8 9 7 LPC1700 Code Bundle Download http ics nxp com support software code bundle lpc17xx keil Documentation http ics nxp com literature presentations microcontrollers pdf code bundle lpc17xx keil uart pdf 8 Plugable USB to RS 232 DB9 Serial Adapter Amazon http www amazon com Plugable Adapter Prolific PL2303HX Chipset dp B00425S1H8 ref sr_1_1 ie UTF8 amp qid 1359988639 amp sr 8 1 amp keywords plugable usbttotserial Tigerdirect http www tigerdirect com applications SearchTools item details asp EdpNo 3753055 amp Catld 464 10
15. ction void UARTO_IRQHandler void is the UARTO interrupt handler Its name is UART0O_IRQHandler because it is named like that by the startup code inside the file startup_LPC17xx s DCD is an assembler directive or pseudo op that defines a 32 bit constant To get a better idea about these things we need to make a parenthesis and discuss a bit about interrupts in the next section For the time being this discussion is enough We will discuss interrupts in more details in class lectures and in some of the next labs as well d Interrupts a 1 encounter An interrupt is the automatic transfer of software execution in response to a hardware event that is asynchronous with the current software execution This hardware event is called a trigger The hardware event can either be a busy to ready transition in an external I O device i e peripheral like for example the UART input output or an internal event like bus fault memory fault or a periodic timer When the hardware needs service signified by a busy to ready state transition it will request an interrupt by setting its trigger flag A thread is defined as the path of action of software as it executes The execution of the interrupt service routine ISR is called as a background thread which is created by the hardware interrupt request and is killed when the ISR returns from interrupt e g by executing a BX LR in an assembly program A new thread is created for each interrupt request In
16. en on page 300 of the LPC17xx User s Manual This fact is captured in the struct declaration of LPC_UART_TypeDef inside the header file LPC17xx h open this file and double check it As a result in our C programming we can refer to the IER register as in the instruction that we are currently discussing LPC_UART0 gt IER which basically stores represents the address 0x4000C004 In addition note that IER_THRE and IER_RLS are declared inside the header file uart h as define IER THRE 0x02 define IER RLS 0x04 Which are utilized as masks in our instruction LPC_UARTO gt I ER ITER THRE ee ER RLS Disable RBR So finally as we see the effect of this instruction is simply to turn 1 bit index 1 the second LSB out of 32 bits and bit index 2 the third LSB out of 32 bits of the IER register All other bits are set to 0 Having bit index 1 of this register set to 1 enables the Transmit Holding Register Empty THRE flag for UARTIO see page 302 Table 275 of the LPC17xx User s Manual Having bit index 2 of this register set to 1 enables the UARTO RX line status interrupts see page 302 Table 275 of the LPC17xx User s Manual As already said all other bits are set therefore via this masking to 0 This includes the LSB i e bit index 0 out of 32 bits of IER register which is set to 0 The role of this bit as explained in the LPC17xx User s Manual on page 302 wh
17. en set to 0 is to disable the Receive Data Available interrupt for UARTO You should be able now to explain what the following instruction does LPC_UARTO gt IER IER_THRE IER RLS IER _RBR Re enable RBR Summarizing what the code inside uarttest c does is as also mentioned in the previous section disable receiving data send back data to the PC from the buffer i e array variable UARTOBuffer reset counter of characters stored in buffer enable receiving data Note As mentioned in lab 1 in general one would not need to worry about these details about addresses to which registers are mapped It would be sufficient to just know of for example the definition and declaration of LPC_UART_TypeDef inside the header file LPC17xx h To the C programmer it is transparent to what exact address the register IER is mapped to for example However now at the beginning it s instructive to track these things so that we get a better global picture of these concepts It also forces us to get better used with the LPC17xx User s Manual and the datasheets Notice that inside the source file uart c we have these two function descriptions void UARTO IRQHandler void void UART1 IRQHandler void which are not called for example inside uarttest c but they appear inside startup_LPC17xx s DCD UART 0 1 ROHandler 21 UARTO DCD UART1 IROHandler 22 UARTI The fun
18. n the NVIC i e activate set priority enable source in NVIC This activation is in addition to the arm and enable steps discussed earlier Table 50 in the User Manual page 73 lists the interrupt sources for each peripheral function Table 51 page 76 in User Manual summarizes the registers in the NVIC as implemented in the LPC17xx microcontroller Read the entire Chapter 6 of the User Manual pages 72 90 and identify the priority and enable registers and their fields of the NVIC Pay particular attention to i e search watch for UARTO in this Chapter How would you set the priority and enable UARTO as a source of interrupts Coming back to our discussion of the function void UARTO_IRQHandler void in uart c we see a first instruction IIRValue LPC_UARTO gt IIR What does it do It simply reads the value of LPC_UARTO gt IR and assigns it to a variable whose name is HRValue LPC_UARTO0 gt IIR is the value of the register IR Interrupt IDentification Register identifies which interrupt s are pending which is one of several 14 of them registers associated with the UARTO peripheral device You can see it as well as the other registers on page 300 of the User Manual Take a while and read them all The fields of the interrupt register HR are later described on page 303 in the User Manual Take another while and read them all on pages 303 304 Next inside uart c we see IIRValue gt gt 1 skip pending bit in IIR
19. ransmission starts the transmitter and receiver must agree on a set of parameters in advance which include the baud rate i e number of bits per second the number of data bits and stop bits and use of parity bit To understand how the UART s receiver extracts encoded data assume it has a clock running at a multiple of the baud rate e g 16x Starting in the idle state as shown in Fig 3 the receiver samples its RX signal until it detects a high low transition Then it waits 1 5 bit periods 24 clock periods to sample its RX signal at what it estimates to be the center of data bit 0 The receiver then samples RX at bit period intervals 16 clock periods until it has read the remaining 7 data bits and the stop bit From that point this process is repeated Successful extraction of the data from a frame requires that over 10 5 bit periods the drift of the receiver clock relative to the transmitter clock be less than 0 5 periods in order to correctly detect the stop bit idle start TX gt A_o Xai PUL ee N cs amp clock 16x Figure 3 Illustration of signal decoding UARTSs can be used to interface to a wide variety of other peripherals For example widely available GSM GPRS cell phone modems and Bluetooth modems can be interfaced to a microcontroller UART Similarly GPS receivers frequently support UART interfaces The NXP LPC1768 microcontroller includes four such devices peripherals called UARTs UARTO 2 3 and UARTI
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