Reading from serial port fails
linux, serial-port
Solution
`read()` returning 0 indicates the end-of-file condition. You should check for that and break out of the loop if it occurs.
As to what's causing that - end-of-file on a serial port indicates it has detected a hangup, meaning that the DCD line has been dropped.
You can set the `CLOCAL` flag in `options.c_cflag` to ignore the modem control lines, if your device doesn't set them properly.
Problem
I have the following C program: ``` #include <fcntl.h> #include <termios.h> #include <stdio.h> int main() { int fd = open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NONBLOCK); if(fd < 0) { perror("Could not open device"); } printf("Device opened\n"); struct termios options; tcgetattr(fd, &options); cfmakeraw(&options); cfsetispeed(&options, B19200); cfsetospeed(&options, B19200); tcsetattr(fd, TCSANOW, &options); char txpacket[] = {0x23, 0x06, 0x00, 0x00, 0xdd, 0xf9}; ssize_t written = write(fd, txpacket, sizeof(txpacket)); printf("Written %d bytes\n", written); printf("Starting to wait for target to respond\n"); while(1) { fd_set readset; FD_ZERO(&readset); FD_SET(fd, &readset); int nCount = select(fd + 1, &readset, NULL, NULL, NULL); if(nCount > 0) { if(FD_ISSET(fd, &readset)) { int i; char buffer[128]; ssize_t bytesread = read(fd, buffer, sizeof(buffer)); printf("Received %d bytes\n", bytesread); for(i = 0; i < bytesread; i++) { printf(" %02x", buffer[i]); } } } } } ``` This program opens the serial device /dev/ttyS0, writes a sequence of data to it and starts listening for a response. I get the following output: ``` Device opened Written 6 bytes Starting to wait for target to respond Received 0 bytes Received 0 bytes Received 0 bytes Received 0 bytes Received 0 bytes Received 0 bytes ... ``` And the application consumes 100% CPU. I'm not able to receive any data, even though the target hardware actually transmits it. What is wrong?