linux-----------串口设置缓冲器的大小_xmit_fifo_size

作者：我家小花儿 | 2024-05-05 15:02:53

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xmit_fifo_size

转自:http://stackoverflow.com/questions/10815811/linux-serial-port-reading-can-i-change-size-of-input-buffer

You want to use the serial IOCTL TIOCSSERIAL which allows changing both receive buffer depth and send buffer depth (among other things). The maximums depend on your hardware, but if a 16550A is in play, the max buffer depth is 14.

You can find code that does something similar to what you want to do here

一下转自:http://e2e.ti.com/support/embedded/linux/f/354/t/164893.aspx

Hello,

I need to send a character (acknowledgement) after reception of a telegram
within no more than 2ms. Before beginning the real application, I wrote a
small test program, to measure the latency. Very strange: sometimes the
latency is about 3ms, sometimes about some �s only, but never other values,
than these 2.
For testing, I send about 3 times per second the telegram "abcdefghij" from
another system to my serial interface.

Perhaps, I need some more information about the fifos: are there tx and rx
fifos, where and how should I configure them?

Here is my test-program with some more detailed questions:

/* I tried 0, 1, 10 and 16, but it does not seem to change anything... */
#define FIFO_SIZE 1

/* This is needed, if not, we can get up to 10ms latency. */
#define TEST_LOW_LATENCY 1

/* If 1, than it seems, some transmissions get lost... */
#define TEST_OUTPUT_FLUSH 0

/* Perhaps only useful with heavy load... */
#define TEST_SCHED 1

#include <sched.h>
#include <sys/ioctl.h>
#include <linux/serial.h>
#include <unistd.h>
#include <termios.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <stdio.h>
#include <strings.h>

#define _POSIX_SOURCE 1
#define DEVICE "/dev/ttyS0"
#define FRAME_SIZE 10 // "abcdefghij"

int fd;

void serial_init()
{
struct termios options;
struct serial_struct serial;
if((fd = open(DEVICE, O_RDWR | O_NOCTTY)) < 0){
perror(DEVICE);
exit(-1);
}
ioctl(fd, TIOCGSERIAL, &serial);
#if TEST_LOW_LATENCY
serial.flags |= ASYNC_LOW_LATENCY;
#else
serial.flags &= ~ASYNC_LOW_LATENCY;
#endif
serial.xmit_fifo_size = FIFO_SIZE; // what is "xmit" ??
ioctl(fd, TIOCSSERIAL, &serial);

tcgetattr(fd, &options);
cfsetispeed(&options, B19200);
cfsetospeed(&options, B19200);
options.c_cflag &= ~(CSIZE | PARODD | CSTOPB | CRTSCTS);
options.c_cflag |= CLOCAL | CREAD | CS8 | PARENB;
options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
options.c_iflag |= INPCK | ISTRIP;
options.c_oflag &= ~OPOST;
options.c_cc[VTIME] = 1;
options.c_cc[VMIN] = FRAME_SIZE;
tcsetattr(fd, TCSANOW, &options);
}

int check_frame()
{
char buf[FRAME_SIZE + 1];
while(!read(fd, buf, FRAME_SIZE));
buf[FRAME_SIZE] = '\0';
puts(buf);
return buf[FRAME_SIZE - 1] == 'j';
}

void serial_ack()
{
write(fd, "a", 1);
#if TEST_OUTPUT_FLUSH
tcflush(fd, TCOFLUSH);
#endif
}

int main()
{
#if TEST_SCHED
struct sched_param sched;
sched_getparam(0, &sched);
sched.sched_priority = 50;
sched_setscheduler(0, SCHED_RR, &sched);
#endif
serial_init();
while(1)
if(check_frame())
serial_ack();
else
puts("Error");
return 0;
}

I would be glad about any hint!
Greetings, Peter

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