CSC231 Lab 7

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CSC 231 Lab # 7

© D. Thiebaut, 2008

Before you start, you will need to setup the Ubuntu the same way we did in Lab #6, so that you are in the root folder of ubuntu, logged in as root, and you have copied your environment from the USB stick to your Ubuntu root account.

Input/Output PC to Arduino: Part I

In this first part you will enter commands at the Linux prompt to set the Arduino LED 13 On and Off, or to read the status of various pins.

Don't miss the presentation that will be done in class. We'll go over the 3 programs involved in today's lab.

The Arduino program: arduino_loop.pde

• First take a close look at the program that runs on the arduino: arduino_loop.pde, whose code is available here. Notice how the loop function continuously store incoming characters in the buffer until a \n character is found, in which case the contents of the buffer is analyzed, the command identified, and executed.

• Cut and paste arduino_loop.pde in the arduino GUI on your Ubuntu machine.

• Compile it.

• Upload it to the Arduino.

The C-Program running on the Ubuntu: arduino-serial.c

• Take a close look at arduino-serial.c . It is the program running on the Ubuntu PC/laptop. You should copy/paste it into an emacs window and save it to your

• compile the program as follows:

gcc  -o  arduino-serial  arduino-serial.c

• run it as follows:

 ./arduino-serial -b 9600 -p /dev/ttyUSB0  -s "w d 13 1"

where -b is the switch used to set the communication speed (9600 baud--very slow), -p is used to set the port associated with the USB connection, and -s means Send a message to the arduino. Here the message is Write a 1 on Digital Pin 13 of the arduino.

• Try to read the digital pins, too:

 ./arduino-serial -b 9600 -p /dev/ttyUSB0 -s "r d" -r

In this case you make the program send a string first (the request to read), and receive next. In receive mode, the arduino-serial program simply wait and fills a buffer with characters received until it gets a '\n' character. Then it displays what it has received.

EXERCISE #1 Modify the command line so that you will turn Pin 13 ON, then OFF, then ON, then OFF again.

EXERCISE #2 Look at the code of serial-arduino.c and figure out how you can make the program wait for a few ms or seconds between commands. Once you have figure this out, repeat Exercise 1 but make the LED stay ON for a second before being turned OFF, and similarly make it stay OFF a second before being turnd ON again.

EXERCISE #3 Take a wire and connect it between Pin 3 of the Arduino connector and Ground. Use serial-arduino to request a list of the values currently on the digital pins. Identify Pin 3 in the list of 0s and 1s (you will need to see how arduino_loop.pde generates the string of 1s and 0s). Now connect Pin 3 to Vcc using the same wire. Now Pin 3 sees a high voltage. Use serial-arduino to read the digital pins Verify that you can read the changing value of Pin 3 this way.nbsp;

The Assembly Program

Step 1: C + asm = new program

You will have probably noticed the two commented lines in serial-arduino containing asm_main in them, one to indicate that asm_main is extern, i.e. defined somewhere else, and one to call it at the end of the loop that processes the command line arguments.

• Uncomment the two asm_main statements, please.

• On the Ubuntu PC, open emacs and create a file called talkToArduino.asm

;;; talkToArduino.asm
;;; D. Thiebaut
;;; 
;;;  nasm -f elf talkToArduino.asm
;;;  gcc -o talkToArduino  arduino-serial.c  talkToArduino.o
;;;

;;; ----------------------- EXTERN LABELS -----------------------
extern serialport_writebyte	; int function
extern serialport_write		; int function
extern serialport_read_until	; int function
extern displayBuffer		; int function
	
extern buf	
extern byte		
        
        ;; -------------------------
        ;; data segment
        ;; -------------------------
        section .data
msg1	db	"w d 13 1", 0
msg1len	equ	$-msg1
	
	
        
        ;; -------------------------
        ;; code area
        ;; -------------------------
        section .text
        global  asm_main
asm_main:
	
	;; turn Pin 13 On 
  	mov	eax, msg1
  	mov	ecx, msg1len
  	call	copyMsg                     ;create copy of msg1 in buf, in C prog
  	call	serialport_write           ;call function in C prog

	
        ;; return to C program
	
        ret

;;; ----------------------------------------------------------------
;;; copyMsg1: puts array whose address in eax  in external buffer
;;; 	      number of bytes shoudl be in ecx.
;;; ----------------------------------------------------------------
copyMsg:
	pushad
	mov	esi, eax	; source buffer
	mov	edi, buf	; destination buffer in C program
.for	mov	al, [esi]
	mov	[edi], al
	inc	esi
	inc	edi
	loop	.for
	popad
	ret

• Assemble the program and link it with the C program:

nasm -f elf talkToArduino.asm

gcc -o arduino-serial  arduino-serial.c  talkToArduino.o

• Make sure Pin 13 is off. Then run the program, but without specifying any options relating to the pins. This time we want the assembly program to do the work!

./arduino-serial -b 9600 -p /dev/ttyUSB0

Did the pin turn off? If not, there's a problem with your setup. Double check everything we have done so far.

Step 2: More assembly

EXERCISE #4 Modify the assembly language program and add another message, msg2, that can be used to turn Pin 13 Off. Modify the body of the asm_main function so that it will turn Pin 13 ON and OFF a few times.