lab4 - Cristinel Ababei
Contents
1. Pong P Chu FPGA Prototyping by VHDL Examples Xilinx Spartan 3 Version Wiley 2008 Chapter 7 Lab manual of course http www cs indiana edu geobrown book pdf 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 4 UART entry on Wikipedia click also on the references therein for RS 232 http en wikipedia org wiki Universal_asynchronous_receiver transmitter 5 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 6 Pluggable USB to RS 232 DB9 Serial Adapter Amazon http www amazon com Plugable Adapter Prolific PL2303HX Chipset dp B00425S 1H8 ref sr_1_1 ie UTF8 amp gid 1359988639 amp sr 8 1 amp keywords plugable usb to serial Tigerdirect http www tigerdirect com applications SearchTools item details asp EdpNo 3753055 amp CatIld 4642. a first instruction IIRValue LPC _UARTO gt IIR What does it do It simply reads the value of LPC_UARTO gt IIR and assigns it to a variable whose name is TRValue LPC_UARTO0 gt IIR is the value of the register IIR 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 309 of the User Manual Take a while and read them all The fields of the interrupt register IIR are later described on page 312 in the User Manual Take another while and read them all on page 312 Next inside uart c we see IIRValue gt gt 1 skip pending bit in IIR IIRValue amp 0x07 check bit 1 3 interrupt identification Which shifts right with one bit IRValue and then AND s it with 0x07 This effectively zooms in onto the field formed by bits index 1 3 from the original LPC_UARTO gt IIR bits which are now in the position bits index 0 2 of IIRValue variable Going on we find an if instruction with several branches if IIRValue IIR_RLS Receive Line Status else if IIRValue IIR_RDA Receive Data Available s else if IIRValue IIR_CTI Character timeout indicator else if IIRValue IIR THRE THRE transmit holding register empty Read Table 277 page 312 in the User Manual to see the meani
3. includes a common library peripheral APIs and test modules for the APIs These examples were put together for ARM s boards However because LandTiger 2 0 board bears a lot of similarities with ARM s MCB1700 board most of these examples can be adapted fairly easily to make them work on the LandTiger 2 0 board For instance in this lab we work with an adapted version of the UART example from the LPC1700 code bundle All the required source files for this example are located under Example1 folder that comes with the archive of files provided for this lab Create a new uVision project and add all the provided files to your project Before doing anything first make sure you remove the ISP and RST jumpers of the LandTiger 2 0 board these are the jumpers marked as JP6 and JP7 on the board next to the actual COM connectors Step 1 Connect the board COM1 and the host computer using the serial cable Step 2 Familiarize yourself with the following files uart c contains the UARTO UART2 handlers driver functions uarttest c contains a small test program Step 3 Build the project and download to target 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 bo
4. 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 UARTO_Count e Once the transmission of all characters from the buffer is done reset the counter UARTO_Count 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 SystemInitQ This is described in source file system_LPC17xx c Place the mouse cursor on SystemInit then right click and select Go to the Definition of SystemInit Try to understand how this function is implemented what each of the source code lines do A function call UARTInit 0 9600 This function is described in source file uart c The declaration of this function is done inside the header file uart h Open these files and read the whole code try to understand each line of the code 4 An instruction LPC _UARTO gt IER IER THRE IER RLS Disable RBR Based on what s been studied in the previous labs we should know already that LPC_UARTO is an address of a memory location the UAR
5. Lab 4 Using UART COEN 4720 Embedded Systems Cristinel Ababei Dept of Electrical and Computer Engineering Marquette University 1 Objective The objective of this lab is to utilize the Universal Asynchronous Receiver Transmitter UART to connect the LandTiger 2 0 board to the host computer We ll continue to discuss the concept of interrupts 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 printed in a terminal 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 A commonly used device for enc
6. PC17xx User s Manual 1 See also page 27 of the Datasheet 2 UARTO and UART2 of the microcontroller are connected on the LandTiger 2 0 board to the SP3232 U10 on the board s schematic diagram which converts the logic signals to RS 232 voltage levels This connection is realized from pins P0 2 and P0 3 and P0 10 and P0 11 of the microcontroller to the pins 9 10 11 and 12 SP3232 chip To confirm this please take a look at the board s schematic diagram provided as file 0_ HY_LandTiger_SCH pdf page 6 inside the files archive of lab 2 Also take some time to read Section 2 12 of the board s manual provided as file 1_HY_LandTiger_v20_user_manual_v11 pdf pages 18 19 inside the files archive of lab 2 The SP3232 chip drives the two COM1 and COM2 represented by the two female DB9 connectors on the board For more details on UART and RS 232 please read references 1 4 In this lab we will explore serial communication between the target LPC1768 UART and a serial communication port of the host PC 3 Examplel Microcontroller echoes back the characters sent by host computer a Experiment In the first example of this lab we ll use an adapted to the LandTiger 2 0 board example project that comes with the LPC1700 code bundle 5 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
7. TO 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 309 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 From a C programming perspective LPC_UARTO is declared inside header file LPC17xx h define LPC_UARTO LPC_UART_TypeDef LPC_UARTO BASE Which also declares what LPC_UART0O_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 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 seen on page 309 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
8. ard for example For the HyperTerminal settings you should use COM1 double check that it the host s serial port is indeed COM 1in 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 9600 8 data bits no parity 1 stop bit and no flow control Method 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 COMI or whatever is in your case find what it is as described in Method 1 baud rate 9600 8 data bits no parity 1 stop bit and no flow control Click on Session and choose the type of connection as Serial Save the session for example as lab4 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 Ty
9. in our C programming we can refer to the IER register as in the instruction that we are currently discussing LPC_UARTO0 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 IER IER THRE IER 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 UARTO see Table 276 page 311 of the LPC17xx User s Manual Having bit index 2 of this register set to 1 enables the UARTO RX line status interrupts 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 311 when 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 Su
10. itter 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 sx Ao X11 PUTT Me 2 ade al amp clock 16x Figure 3 Illustration of signal decoding UARTs 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 UART1 See pages 307 and 327 of the L
11. mmarizing what the code inside uarttest c does is disable receiving data send back data to the PC from the buffer i e array variable UARTO_Buffer reset counter of characters stored in buffer enable receiving data Note As mentioned in previous labs 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 5 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 of this class 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 UART2 IRQHandler void which are not called for example inside uarttest c but they appear inside startup_LPC17xx s DCD UARTO IRQHandler DCD UART2 IRQHandler The function void UARTO_IRQHandler void is the UARTO interrupt handler Its name is UARTO_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 Inside this function we see
12. ng of the three bits 1 3 from the original IIR 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 312 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 1 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 2 Modify Example 1 such that the characters typed on the host s keyboard are also displayed on the LCD display on the board 5 Credits and references 1 LPC17xx user s manual http www nxp com documents user_manual UM10360 pdf part of lab 2 archive of files 2 NXP LPC17xx Datasheet http www nxp com documents data_sheet LPC1769_68 67 66 _65_64 63 pdf also part of lab 2 files archive of files 3 Jonathan W Valvano Embedded Systems Introduction to Arm Cortex M3 Microcontrollers 2012 Chapters 8 9
13. oding 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 s Stop bit Figure 2 Transmission of a byte No clock information is conveyed through the serial line Before the transmission starts the transm
14. pe some text The text 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 text 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 COM1 and connect it to COM2 port on the LandTiger 2 0 board The behavior of project should be the same as I hope you expected b Brief program description Looking at the main function inside the uarttest c file we can see the following main actions UARTO and UART2 are initialized UARTInit 0 9600 UARTInit 2 9600 A while loop which executes indefinitely either for UARTO or for UART2 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 page 311 when set to 0 is to disable the Receive Data Available interrupt for UARTO e Send back to the host the characters from the buffer UARTO_Buffer This is done only if there are characters in
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