Messages in this thread | | | Date | Thu, 20 Nov 2008 11:06:19 +0100 (CET) | From | Thomas Pfaff <> | Subject | Question about TTY_DO_WRITE_WAKEUP |
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I have written a program that reads and writes data to the serial uart using async io. Unfortunately it does not work properly because a SIGIO is never gerated when output becomes possible, the reason is that TTY_DO_WRITE_WAKEUP is not set for most of the tty drivers. After i set the bit in serial_core.c the program works as expected. Now i wonder why TTY_DO_WRITE_WAKEUP is almost always disabled ?
Below is a test case.
Thank you in advance,
Thomas
#include <stdlib.h> #include <unistd.h> #include <signal.h> #include <string.h> #include <stdlib.h> #include <sys/fcntl.h> #include <termios.h> #include <errno.h>
static const char outbuf [] = "01234567890abcdef\n";
static void sigio_handler (int sig __attribute__((unused))) { }
static int sigact (int sig, void (*handler)(int)) { struct sigaction sa;
memset (&sa, 0, sizeof (sa));
sa.sa_flags = SA_NOCLDWAIT | SA_NOCLDSTOP; sigfillset (&sa.sa_mask); sa.sa_handler = handler;
return sigaction (sig, &sa, NULL); }
static int uart_set_termio (int fd) { struct termios term;
if (tcgetattr (fd, &term) == -1) return -1;
term.c_cflag = B19200 | CS8 | CREAD | CLOCAL; term.c_iflag = IGNPAR; term.c_oflag = 0; term.c_lflag = 0;
term.c_cc [VTIME] = 0; term.c_cc [VMIN] = 0;
return tcsetattr (fd, TCSAFLUSH, &term); }
static int uart_fd_init (int fd) { if (fcntl (fd, F_SETSIG, 0) == -1 || fcntl (fd, F_SETOWN, getpid ()) == -1) return -1;
return fcntl (fd, F_SETFL, fcntl (fd, F_GETFL) | O_ASYNC | O_NONBLOCK); }
static int uart_sig_init (void) { sigset_t sigset;
if (sigact (SIGIO, sigio_handler) == -1) return -1;
if (sigemptyset (&sigset) == -1 || sigaddset (&sigset, SIGIO) == -1) return -1;
return sigprocmask (SIG_BLOCK, &sigset, NULL); }
int main (int argc, char *argv []) { int uart_fd; sigset_t sigmask; const int outbuflen = strlen (outbuf); const char *dev = "/dev/ttyS0";
if (argc > 1) dev = argv [1];
if (uart_sig_init () == -1) return EXIT_FAILURE;
uart_fd = open (dev, O_RDWR | O_NOCTTY | O_NONBLOCK); if (uart_fd == -1) return EXIT_FAILURE;
if (uart_set_termio (uart_fd) == -1 || uart_fd_init (uart_fd) == -1) return EXIT_FAILURE;
if (sigprocmask (SIG_SETMASK, NULL, &sigmask) == -1 || sigdelset (&sigmask, SIGIO) == -1) return EXIT_FAILURE;
while (1) { int written; int towrite = outbuflen; const char *buf = outbuf;
while (towrite) { written = write (uart_fd, buf, towrite); if (written == -1) { if (errno == EAGAIN) { sigsuspend (&sigmask); continue; } else return EXIT_FAILURE; }
buf += written; towrite -= written; } }
return EXIT_SUCCESS; }
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