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POClear data at serial port in Linux in C?
 

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  1. POClear data at serial port in Linux in C?
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    <p>I am testing the sending and receiving programs with the code as</p> <p>The main() function is below:</p> <pre> <code>#include "lib.h" int fd; int initport(int fd) { struct termios options; // Get the current options for the port... tcgetattr(fd, &options); // Set the baud rates to 19200... cfsetispeed(&options, B9600); cfsetospeed(&options, B9600); // Enable the receiver and set local mode... options.c_cflag |= (CLOCAL | CREAD); options.c_cflag &= ~PARENB; options.c_cflag &= ~CSTOPB; options.c_cflag &= ~CSIZE; options.c_cflag |= CS8; // Set the new options for the port... tcsetattr(fd, TCSANOW, &options); return 1; } int main(int argc, char **argv) { fd = open("/dev/pts/2", O_RDWR | O_NOCTTY | O_NDELAY); if (fd == -1) { perror("open_port: Unable to open /dev/pts/1 - "); return 1; } else { fcntl(fd, F_SETFL, 0); } printf("baud=%d\n", getbaud(fd)); initport(fd); printf("baud=%d\n", getbaud(fd)); char sCmd[254]; sCmd[0] = 0x41; sCmd[1] = 0x42; sCmd[2] = 0x43; sCmd[3] = 0x00; if (!writeport(fd, sCmd)) { printf("write failed\n"); close(fd); return 1; } printf("written:%s\n", sCmd); usleep(500000); char sResult[254]; fcntl(fd, F_SETFL, FNDELAY); if (!readport(fd,sResult)) { printf("read failed\n"); close(fd); return 1; } printf("readport=%s\n", sResult); close(fd); return 0; } </code> </pre> <p>The lib.h contains read and write code as at:</p> <p><a href="https://stackoverflow.com/questions/2500567/parse-and-read-data-frame-in-c">Parse and read data frame in C?</a></p> <p>and got the issue:</p> <p>In order to test with serial port, I used the socat (<a href="https://help.ubuntu.com/community/VirtualSerialPort" rel="nofollow noreferrer">https://help.ubuntu.com/community/VirtualSerialPort</a> ) to create a pair serial ports on Linux and test my program with these port.</p> <p>The first time the program sends the data and the program receives data is ok. However, if I read again or even re-write the new data into the serial port, the return data is always null until I stop the virtual serial port and start it again, then the write and read data is ok, but still, only one time.</p> <p>(In the real case, the sending part will be done by another device, I am just taking care of the reading data from the serial port. I wrote both parts just to test my reading code.)</p> <p>Does anyone have any ideas?</p>
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    1. COI see one bug (possibly unrelated to your question): Don't assign to `result[iIn-1]` before verifying that `iIn1 > 0`
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      1. USDavid Gelhar
    2. COCould you please explain why that? and by the way, I wrote iIn < 0 not iIn > 0
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