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annotate libserial-newlnx/openport.c @ 611:c847d742ab38

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doc/Loadtools-performance: article started
author Mychaela Falconia <falcon@freecalypso.org>
date Mon, 24 Feb 2020 21:44:13 +0000
parents 9d9c241f2c84
children f82551c77e58
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1 /*
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2 * This module implements the basic serial port opening operation.
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3 */
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4
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5 #include <sys/types.h>
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6 #include <sys/file.h>
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7 #include <sys/ioctl.h>
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8 #include <linux/serial.h>
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9 #include <stdio.h>
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10 #include <stdlib.h>
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11 #include <unistd.h>
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12
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13 int target_fd;
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14
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15 open_serial_port(ttyport)
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16 char *ttyport;
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17 {
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18 struct serial_struct kernel_serial_settings;
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19
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20 target_fd = open(ttyport, O_RDWR|O_NONBLOCK);
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21 if (target_fd < 0) {
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22 perror(ttyport);
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23 exit(1);
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24 }
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25 ioctl(target_fd, TIOCEXCL);
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26 /*
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27 * It appears that some miscreants have modified recent Linux kernel
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28 * versions (newer than linux-4.4.14 of Slackware 14.2) to insert
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29 * a delay of 10 ms before select system call returns when serial
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30 * input is ready; this Linux kernel misbehaviour majorly slows down
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31 * many of our operations. It appears that we need to set the
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32 * ASYNC_LOW_LATENCY flag in TIOCSSERIAL in order to get the old
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33 * sane behaviour back.
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34 */
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35 ioctl(target_fd, TIOCGSERIAL, &kernel_serial_settings);
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36 kernel_serial_settings.flags |= ASYNC_LOW_LATENCY;
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37 ioctl(target_fd, TIOCSSERIAL, &kernel_serial_settings);
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38 return 0;
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39 }