一、硬件电路
1.1、硬件外扩的io接口原理图
二、查看串口操作目录
2.1、操作串口的目录为/sys/class/tty
root@localhost:~# ls /sys/class/tty/
2.2、USB串口为串口1，实际调用的是/dev/ttyS0，在此使用的串口是UART2,所以软件当中调用的是ttyS1
三、串口程序
3.1、程序代码
/* Copyright 2018 Tronlong Elec. Tech. Co. Ltd. All Rights Reserved. */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/select.h>
#include <sys/time.h>
#include <fcntl.h>
#include <termios.h>
#include <string.h>
#include <errno.h>
#include <stdbool.h>
#include <libgen.h>
#include <signal.h>
#include <getopt.h>
#define NOPASS_CONDITIONS 3
#define INADEQUATE_CONDITIONS 10
enum Mode { READ, WRITE, LOOPBACK };
/* Exit flag */
volatile bool g_quit = false;
/* Short option names */
static const char g_shortopts [] = ":d:s:rwvhl";
/* Option names */
static const struct option g_longopts [] = {
{ "device", required_argument, NULL, 'd' },
{ "read", no_argument, NULL, 'r' },
{ "write", no_argument, NULL, 'w' },
{ "loopback", no_argument, NULL, 'l' },
{ "size", required_argument, NULL, 's' },
{ "version", no_argument, NULL, 'v' },
{ "help", no_argument, NULL, 'h' },
{ 0, 0, 0, 0 }
};
static void usage(FILE *fp, int argc, char **argv) {
fprintf(fp,
"Usage: %s [options]\n\n"
"Options:\n"
" -d | --device Device such as '/dev/ttyS0'\n"
" -r | --read Read\n"
" -w | --write Write\n"
" -l | --loopback loopback test\n"
" -s | --size Read size\n"
" -v | --version Display version information\n"
" -h | --help Show help content\n"
" e.g. ./tl-uart-rw -d /dev/ttyS1 -r -s 256\n"
" ./tl-uart-rw -d /dev/ttyS1 -w -s 1024\n"
" ./tl-uart-rw -d /dev/ttyS1 -l -s 1024\n\n"
"", basename(argv[0]));
}
static void opt_parsing_err_handle(int argc, char **argv, int flag) {
/* Exit if no input parameters are entered */
int state = 0;
if (argc < 2) {
printf("No input parameters are entered, please check the input.\n");
state = -1;
} else {
/* Feedback Error parameter information then exit */
if (optind < argc || flag) {
printf("Error: Parameter parsing failed\n");
if (flag)
printf("\tunrecognized option '%s'\n", argv[optind-1]);
while (optind < argc) {
printf("\tunrecognized option '%s'\n", argv[optind++]);
}
state = -1;
}
}
if (state == -1) {
printf("Tips: '-h' or '--help' to get help\n\n");
exit(2);
}
}
void sig_handle(int arg) {
g_quit = true;
}
int init_serial(int *fd, const char *dev) {
struct termios opt;
/* open serial device */
if ((*fd = open(dev, O_RDWR)) < 0) {
perror("open()");
return -1;
}
/* define termois */
if (tcgetattr(*fd, &opt) < 0) {
perror("tcgetattr()");
return -1;
}
opt.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
opt.c_oflag &= ~OPOST;
/* Character length, make sure to screen out this bit before setting the data bit */
opt.c_cflag &= ~CSIZE;
/* No hardware flow control */
opt.c_cflag &= ~CRTSCTS;
/* 8-bit data length */
opt.c_cflag |= CS8;
/* 1-bit stop bit */
opt.c_cflag &= ~CSTOPB;
/* No parity bit */
opt.c_iflag |= IGNPAR;
/* Output mode */
opt.c_oflag = 0;
/* No active terminal mode */
opt.c_lflag = 0;
/* Input baud rate */
if (cfsetispeed(&opt, B115200) < 0)
return -1;
/* Output baud rate */
if (cfsetospeed(&opt, B115200) < 0)
return -1;
/* Overflow data can be received, but not read */
if (tcflush(*fd, TCIFLUSH) < 0)
return -1;
if (tcsetattr(*fd, TCSANOW, &opt) < 0)
return -1;
return 0;
}
int serial_write(int *fd, const char *data, size_t size) {
int ret = write(*fd, data, size);
if ( ret < 0 ) {
perror("write");
tcflush(*fd, TCOFLUSH);
}
return ret;
}
int serial_read(int *fd, char *data, size_t size) {
size_t read_left = size;
size_t read_size = 0;
char *read_ptr = data;
struct timeval timeout = {5, 0};
memset(data, 0, size);
fd_set rfds;
while (!g_quit) {
FD_ZERO(&rfds);
FD_SET(*fd, &rfds);
timeout.tv_sec = 5;
timeout.tv_usec = 0;
if (read_left == 0)
break;
switch (select(*fd+1, &rfds, NULL, NULL, &timeout)) {
case -1:
perror("select()");
break;
case 0:
perror("timeout and retry");
break;
default:
if (FD_ISSET(*fd,&rfds)) {
read_size = read(*fd, read_ptr, read_left);
if (read_size == 0)
break;
read_ptr += read_size;
read_left -= read_size;
}
}
}
return strlen(data);
}
int run_read_mode(char *dev, size_t size) {
char *buf = NULL;
int fd = -1;
int ret = -1;
ret = init_serial(&fd, dev);
if (ret < 0) {
close(fd);
return -1;
}
printf("Mode : read\n");
if (size <= 0) {
printf ("Error : Incorrect size settings\n");
exit(INADEQUATE_CONDITIONS);
}
buf = (char*)malloc(size);
ret = serial_read(&fd, buf, size);
printf("recv: %s\nsize: %d\n", buf, ret);
free(buf);
return 0;
}
int run_write_mode(char *dev, size_t size) {
int fd = -1;
int ret = -1;
ret = init_serial(&fd, dev);
if (ret < 0) {
close(fd);
return -1;
}
printf("Mode : write\n");
if (size <= 0) {
printf("Error : Incorrect size settings\n");
exit(INADEQUATE_CONDITIONS);
}
int i = 0;
char context;
size_t write_size = 0;
while (!g_quit) {
if (i > 7)
i = 0;
context = (char)('0' + i);
write_size += serial_write(&fd, &context, sizeof(context));
i ++;
if (size == write_size)
break;
}
printf("send size: %d\n", write_size);
return 0;
}
int run_loopback_test(char *dev, size_t size) {
int fd;
int ret;
size_t buf_size;
int serial_buf_size;
ret = init_serial(&fd, dev);
if (ret < 0)
return -1;
printf("Start uart loopback testing.\n");
/* Serial port buffer size generally defaults to 2k - 4k */
char *write_buf = (char*)malloc(size);
char *read_buf = (char*)malloc(size);
buf_size = size;
while (buf_size > 0)
{
if(buf_size > 1024) {
serial_buf_size = 1024;
} else {
serial_buf_size = buf_size;
}
// Generate random data to write.
memset(write_buf, rand() % 26 + 65, serial_buf_size);
memset(read_buf, 0, serial_buf_size);
ret = serial_write(&fd, write_buf, serial_buf_size);
/* delay > 1024 / 115200 * 1000000 */
usleep(90000);
ret = serial_read(&fd, read_buf, serial_buf_size);
ret = memcmp(read_buf, write_buf, serial_buf_size);
if (ret != 0) {
printf("Result : Test failed\n");
goto release;
}
buf_size -= 1024;
}
printf("send size: %d\n", size);
printf("recv size: %d\n", size);
printf("Result : Test pass\n");
release:
free(write_buf);
free(read_buf);
close (fd);
if (ret != 0) {
return NOPASS_CONDITIONS;
} else {
return 0;
}
}
int main(int argc, char *argv[]) {
int c = 0;
int flag = 0;
int mode = -1;
size_t size = 0;
char *dev = NULL;
int ret = -1;
/* Parsing input parameters */
while ((c = getopt_long(argc, argv, g_shortopts, g_longopts, NULL)) != -1) {
switch (c) {
case 'd':
dev = optarg;
break;
case 'r':
mode = READ;
break;
case 'w':
mode = WRITE;
break;
case 'l':
mode = LOOPBACK;
break;
case 's':
size = atoi(optarg);
break;
case 'v':
/* Display the version */
printf("version : 1.0\n");
exit(0);
case 'h':
usage(stdout, argc, argv);
exit(0);
default :
flag = 1;
break;
}
}
opt_parsing_err_handle(argc, argv, flag);
/* Ctrl+c handler */
signal(SIGINT, sig_handle);
switch (mode) {
case READ:
if(run_read_mode(dev, size) < 0) {
return INADEQUATE_CONDITIONS;
}
break;
case WRITE:
if(run_write_mode(dev, size) < 0) {
return INADEQUATE_CONDITIONS;
}
break;
case LOOPBACK:
ret = run_loopback_test(dev, size);
if(ret < 0) {
return INADEQUATE_CONDITIONS;
} else if(ret == NOPASS_CONDITIONS) {
return NOPASS_CONDITIONS;
}
break;
default:
break;
}
return 0;
}
3.2、Makefile
tl_uart_rw:tl_uart_rw.c
$(CC) -Wall $< -o $@
clean:
rm -f tl_uart_rw *.o *~
install:
cp tl_uart_rw $(PREFIX)
四、实际操作
感谢分享C串口的示例分享。给出了图示等，非常详细，感谢分享。
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