Serial interface initialisation on Linux systems is a mess and it is easy
to forget something. That's why I would recommend to use a library which
does all the work for you like liboapc
from https://sourceforge.net/p/oapc/code/ci/master/tree/liboapc/
Am Mittwoch, 20. Juli 2016 08:56:50 UTC+2 schrieb Regina Choi:
>
>
> Hi,
>
> I have programmed (in C) UART4 read in thread with blocking read, the code
> as below: I confirmed that the UART receive port does have data through
> oscilloscope, but somehow there is no data in read( ), the return count
> always zero ?
>
> The strange thing is if minicom is open on the Uart4, then the read( ) in
> receive thread started to run as normal. However, the regular file write
> become weird. The string won't be able to be written into file ?!
>
> Btw, my BBB version is 3.8.13-bone47
>
>
> #include<stdio.h>
> #include<stdlib.h> // required for fopen, exit()
> #include<fcntl.h>
> #include<termios.h>
> //#include<string.h>
> #include<unistd.h>
> #include<pthread.h>
> #include "readerComm.h"
>
>
> pthread_t uartRxT , uartTxT;
> int file, file2;
>
> int main (int argc, char* argv[])
> {
> int count;
>
> pthread_attr_t attr;
> void *status;
> FILE *fdata;
>
>
> if(argc != 2)
> {
>
> printf("Invalid number of arguments, exiting!");
> return -2;
>
> }
>
> if((file = open("/dev/ttyO4", O_RDWR | O_NOCTTY | O_NDELAY ))< 0)
> {
> perror("UART: Failed to open the file");
> return -1;
> }
>
> fcntl(file, F_SETFL, 0); // blocking read
> struct termios options; //oriopt
> tcgetattr(file, &options);
> options.c_cflag = B9600 | CS8 | CREAD | CLOCAL;
> options.c_iflag = IGNPAR | ICRNL;
>
> options.c_iflag &= ~IGNBRK;
> options.c_iflag &= ~(IXON | IXOFF | IXANY); // shut off xon/xoff ctrl
>
> options.c_cc[VMIN] = 2; // Non Canonical input mode (as we didnt
> set ICANON for c_lflag)
> options.c_cc[VTIME] = 10; // 1 sec timeout
>
>
> tcflush(file, TCIFLUSH);
>
> tcsetattr(file, TCSANOW, &options);
>
>
> unsigned char cmd[] = {0x11, 0x00, 0x32}; //"Tx From Beaglebone ";
>
> if ((count = write(file, (char*)cmd, 3))<0){
> perror("Failed to write to the output\n");
> return -1;
> }else{
> printf("Byte sent: %d \n", count);
> }
>
> fdata = fopen("capture.dat", "w");
> if (fdata == NULL) {
> printf("I couldn't open capture.dat for writing.\n");
> exit(0);
> }
>
> // save in file ( cannot print to file ??)
> fprintf(fdata, "%s", "test");
> perror("UART: Test comment");
>
>
> pthread_attr_init(&attr);
> pthread_attr_setdetachstate(&
> attr, PTHREAD_CREATE_JOINABLE);
>
> // Create UArt Tx thread
> if(pthread_create(&uartTxT, &attr, &uartTxWait, NULL)){
> perror("GPIO: Failed to create the tx thread");
>
> return -1;
> }
>
> // Create Uart Rx thread
> if(pthread_create(&uartRxT, &attr, &uartRxWait, NULL)){
> perror("GPIO: Failed to create the rx thread");
>
> return -1;
> }
>
> pthread_attr_destroy(&attr);
> pthread_join(uartRxT,&status);
> pthread_join(uartTxT,&status);
>
> close(file); // close first file descriptor
>
> // capture.dat file close
> fclose(fdata);
>
> return 0;
>
> }
>
> // UART RX thread
> void* uartRxWait(void *param){
>
> unsigned char receive[100];
> int count, n;
> fd_set input;
> struct timeval timeout;
>
> //initialize input set
> FD_ZERO(&input);
> FD_SET(file, &input);
>
> timeout.tv_sec=0;
> timeout.tv_usec=0;
>
> while(1){
>
> if ((count = read(file, (void *)receive, 100))<0)
> {
> perror("Failed to read from input \n");
> printf("count = %d\n", count);
> }else{
>
> if(receive[2]==0x32){
> printf("Header received \n");
> }
> printf("Byte received [%d] \n", count);
> printf("Value of Pi = 0x%.2x\n", receive[0]);
>
> }
>
> }
>
> pthread_exit(0);
> }
>
>
> void* uartTxWait(void *param){
>
> usleep(1000000);
> pthread_exit(0);
> }
>
--
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