Lab04 - Serial port access
- Communcation methods

Lab04 - Serial port access

Use cat and picocom for serial line access.

Communcation methods

cat - old method

cat allows to read data from a file or device. The Nucleo board will be present at /dev/ttyACM0. The default speed of the serial port set by the kernel driver is 115200 bd.

cat /dev/ttyACM0

The main issue with serial communication is the proper settings of the communication parameters such as:

communication speed - baudrate
number of bites - usually 8
number of stop-bits - usually 1
parity - in some applications none

Unix environment allows to control the serial line settings by stty command.

stty -F /dev/ttyACM0 -brkint -icrnl -imaxbel -opost -onlcr -isig -icanon -iexten -echo -echoe -echoctl -echoke 115200

picocom

Perform the same task with picocom terminal (help man piccocom). Don't forget to set the proper baud rate (115200).

C app

Serial port open

int hSerial = open( "/dev/ttyUSB0", O_RDWR| O_NONBLOCK | O_NDELAY );
// h = handle

Serial port settings

struct termios o_tty;
// o = object
memset (&o_tty, 0, sizeof o_tty);
iRetVal = tcgetattr (hSerial , &o_tty);

Now, modify the settings appropriately. The best guide for serial port programming in Unix is here: serial port programming guide.

Serial port write

unsigned char chArrCmd[] = {'*', 'I', 'D', 'N', '?', '\r', '\n', '\0'};
int n_written = write( hSerial, chArrCmd, sizeof(chArrCmd)-1 ); // why -1?

Serial port read

char chArrBuf [256];
memset (&chArrBuf , '\0', sizeof(chArrBuf) );

int n = read( hSerial, &chArrBuf , sizeof(chArrBuf) );

Serial port close

close(hSerial);

Recommended includes for this task are: stdio.h, stdlib.h, string.h, unistd.h, fcntl.h, errno.h, termios.h.

Lab Instructions

Download the files provided in link lab04_x.zip.
Compile and upload main.c file to NUCLEO board. Can you explain whats happening in main.c?
Send and receive data to NUCLEO board by using the lab04_sender.cpp and lab04_receiver.cpp. Can you explain what lab04_receiver.cpp and lab04_sender.cppcodes are doing?
NOTICE 1: in every terminal that you want to run lab04_sender.cpp and lab04_receiver.cpp, you need to run the command below to set up your serial communication.

stty -F /dev/ttyACM0 -brkint -icrnl -imaxbel -opost -onlcr -isig -icanon -iexten -echo -echoe -echoctl -echoke 115200

NOTICE 2: make sure that you only send and receive from one source. You wont recieve any data if you listen to NUCLEO with two terminals.
NOTICE 3: reset your board each time before running your code to make sure datas from previous running are not still in board buffer.
NOTICE 4: check that make file for nucleo board is written relative and it does not contain user name of any other person.

Lab Tasks

Change lab04_sender.cpp in a way that strings that are supposed to be sent are passed through the terminal.
Make board blink by sending led1 and led0 commands by lab04_sender.cpp from computer. You can make delays in cpp by

#include<unistd.h>
unsigned int microsecond = 1000000;
usleep(3 * microsecond);//sleeps for 3 second

Modify main.c of NUCLEO board in a way that if an integer (1 digit) is sent to it, adds one and returns back through UART. If one is added to 9, it should return 0, not 10.
expand the exercise above for four digit numbers.

Table of Contents