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);
}
