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comparison libserial-newlnx/openport.c @ 608:9d9c241f2c84

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libserial-newlnx experimental change to set ASYNC_LOW_LATENCY
author Mychaela Falconia <falcon@freecalypso.org>
date Wed, 12 Feb 2020 06:23:22 +0000
parents 6984b76f3def
children f82551c77e58
comparison
equal deleted inserted replaced
607:d5abcbbf7432 608:9d9c241f2c84
3 */ 3 */
4 4
5 #include <sys/types.h> 5 #include <sys/types.h>
6 #include <sys/file.h> 6 #include <sys/file.h>
7 #include <sys/ioctl.h> 7 #include <sys/ioctl.h>
8 #include <linux/serial.h>
8 #include <stdio.h> 9 #include <stdio.h>
9 #include <stdlib.h> 10 #include <stdlib.h>
10 #include <unistd.h> 11 #include <unistd.h>
11 12
12 int target_fd; 13 int target_fd;
13 14
14 open_serial_port(ttyport) 15 open_serial_port(ttyport)
15 char *ttyport; 16 char *ttyport;
16 { 17 {
18 struct serial_struct kernel_serial_settings;
19
17 target_fd = open(ttyport, O_RDWR|O_NONBLOCK); 20 target_fd = open(ttyport, O_RDWR|O_NONBLOCK);
18 if (target_fd < 0) { 21 if (target_fd < 0) {
19 perror(ttyport); 22 perror(ttyport);
20 exit(1); 23 exit(1);
21 } 24 }
22 ioctl(target_fd, TIOCEXCL); 25 ioctl(target_fd, TIOCEXCL);
26 /*
27 * It appears that some miscreants have modified recent Linux kernel
28 * versions (newer than linux-4.4.14 of Slackware 14.2) to insert
29 * a delay of 10 ms before select system call returns when serial
30 * input is ready; this Linux kernel misbehaviour majorly slows down
31 * many of our operations. It appears that we need to set the
32 * ASYNC_LOW_LATENCY flag in TIOCSSERIAL in order to get the old
33 * sane behaviour back.
34 */
35 ioctl(target_fd, TIOCGSERIAL, &kernel_serial_settings);
36 kernel_serial_settings.flags |= ASYNC_LOW_LATENCY;
37 ioctl(target_fd, TIOCSSERIAL, &kernel_serial_settings);
23 return 0; 38 return 0;
24 } 39 }