Add tool that can auto control the DE pin state of RS485.

tools/rs485_control_DE/readme.md

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+## Usage
+### Install Required Libraries
+``` bash
+sudo apt-get install libgpiod-dev
+```
+
+### Compilation
+``` bash
+gcc -o rs485_DE rs485_DE.c -lgpiod
+```
+### Execution
+``` bash
+sudo ./rs485_DE TTY_DIR DE_CHIP DE_LINE [rs485_dir] [EN_CHIP] [EN_LINE]
+```
+### Parameter Explanation
+TTY_DIR: Serial port device name, e.g., /dev/ttyAMA0
+DE_CHIP: gpiochip device number for the DE pin chip, e.g., /dev/gpiochip0 
+DE_LINE: Number of the DE pin, e.g., 0 
+rs485_dir: The directory of the created device file, e.g., "/dev/ttyAMA10"
+EN_CHIP: gpiochip device number for the enable control pin chip (optional), e.g., /dev/gpiochip0 
+EN_LINE: Number of the enable control pin (optional), e.g., 0
+
+## Results
+
+A device file in [rs485_dir] will be created. By utilizing this device file, automatic switching between RS485 transmission and reception states can be effortlessly accomplished.

tools/rs485_control_DE/rs485_DE.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <errno.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <termios.h>
+#include <gpiod.h>
+#include <pty.h>
+
+#define BUFFER_SIZE 256
+#define RS485_CONSUMER "RS485_program"
+
+struct gpiod_chip *chip;
+struct gpiod_line *line;
+
+struct gpiod_chip *rs485_chip;
+struct gpiod_line *rs485_line;
+
+void setup_gpio(char *rs485_de_chip, int rs485_de_line, char *rs485_en_chip, int rs485_en_line)
+{
+ int ret;
+
+ // open GPIO controller
+ chip = gpiod_chip_open(rs485_de_chip);
+ if (!chip) {
+ perror("gpiod_chip_open");
+ exit(EXIT_FAILURE);
+ }
+
+ // request GPIO line
+ line = gpiod_chip_get_line(chip, rs485_de_line);
+ if (!line) {
+ fprintf(stderr, "Failed to get GPIO line %d\n", rs485_de_line);
+ gpiod_chip_close(chip);
+ exit(EXIT_FAILURE);
+ }
+
+ // set GPIO as output
+ ret = gpiod_line_request_output(line, RS485_CONSUMER, 0);
+ if (ret < 0) {
+ fprintf(stderr, "Failed to request GPIO line as output: %s\n", strerror(-ret));
+ gpiod_chip_close(chip);
+ exit(EXIT_FAILURE);
+ }
+ if (rs485_en_chip)
+ {
+ // open GPIO controller
+ rs485_chip = gpiod_chip_open(rs485_en_chip);
+ if (!rs485_chip) {
+ perror("gpiod_chip_open");
+ exit(EXIT_FAILURE);
+ }
+
+ // request GPIO line
+ rs485_line = gpiod_chip_get_line(rs485_chip, rs485_en_line);
+ if (!rs485_line) {
+ fprintf(stderr, "Failed to get GPIO line %d\n", rs485_de_line);
+ gpiod_chip_close(rs485_chip);
+ exit(EXIT_FAILURE);
+ }
+
+ // set GPIO as output
+ ret = gpiod_line_request_output(rs485_line, RS485_CONSUMER, 0);
+ if (ret < 0) {
+ fprintf(stderr, "Failed to request GPIO line as output: %s\n", strerror(-ret));
+ gpiod_chip_close(rs485_chip);
+ exit(EXIT_FAILURE);
+ }
+ gpiod_line_set_value(rs485_line, 1);
+ }
+
+}
+
+void toggle_gpio_high() {
+ gpiod_line_set_value(line, 1);
+}
+
+void toggle_gpio_low() {
+ gpiod_line_set_value(line, 0);
+}
+
+
+int main(int argc, char* argv[]) {
+ int master_fd, slave_fd, tty_fd;
+ char slave_name[32];
+ char *tty_name;
+ struct termios tty_termios;
+ struct termios tty;
+ char buffer[BUFFER_SIZE];
+ ssize_t n;
+ int ready;
+ fd_set readfds, writefds;
+ int rs485_de_line, rs485_en_line;
+ char *rs485_de_chip, *rs485_en_chip , *rs485_dir;
+
+
+ if(argc < 4) {
+ printf("Usage: %s /dev/ttyAMA* DE_CHIP(/dev/gpiochip*) DE_LINE [RS485_dir] [EN_CHIP] [EN_LINE]\n", argv[0]);
+ return 1;
+ }
+
+ tty_name = argv[1];
+ rs485_de_chip = argv[2];
+ rs485_de_line = atoi(argv[3]);
+ rs485_dir = (argc > 4) ? argv[4] : "/dev/ttyAMA10";
+ rs485_en_chip = (argc > 6) ? argv[5] : NULL;
+ rs485_en_line = (argc > 6) ? atoi(argv[6]) : -1;
+
+ setup_gpio(rs485_de_chip, rs485_de_line, rs485_en_chip, rs485_en_line);
+
+ // create pseudo terminal
+ if (openpty(&master_fd, &slave_fd, slave_name, NULL, NULL) == -1) {
+ perror("openpty");
+ return 1;
+ }
+
+ // create symlink
+ if(symlink(slave_name, rs485_dir) == -1) {
+ if(errno != EEXIST) {
+ perror("symlink");
+ return 1;
+ } else {
+ if (unlink(rs485_dir) == -1) {
+ perror("unlink");
+ return 1;
+ }
+ if(symlink(slave_name, rs485_dir) == -1) {
+ perror("symlink");
+ return 1;
+ }
+ }
+ }
+
+ // 0666 permissions
+ chmod(slave_name, 0666);
+
+ printf("slave_name: %s new tty: %s\n", slave_name, rs485_dir);
+ // open serial port
+ tty_fd = open(tty_name, O_RDWR | O_NOCTTY | O_NDELAY);
+ if (tty_fd < 0) {
+ perror("Unable to open serial port");
+ return 1;
+ }
+
+ // set serial port attributes
+ tcgetattr(master_fd, &tty);
+ cfmakeraw(&tty); // set raw mode
+ tcsetattr(master_fd, TCSANOW, &tty);
+ tcsetattr(tty_fd, TCSANOW, &tty);
+ // monitor file descriptors
+ FD_ZERO(&readfds);
+
+ while (1) {
+ FD_SET(master_fd, &readfds);
+ FD_SET(tty_fd, &readfds);
+ int max_fd = (tty_fd > master_fd) ? tty_fd : master_fd;
+ ready = select(max_fd + 2, &readfds, NULL, NULL, NULL);
+ if (ready == -1) {
+ perror("select");
+ break;
+ }
+
+ if (FD_ISSET(master_fd, &readfds)) {
+ toggle_gpio_high();
+ tcgetattr(master_fd, &tty);
+ tcsetattr(tty_fd, TCSANOW, &tty);
+ n = read(master_fd, buffer, BUFFER_SIZE - 1);
+ if (n > 0) {
+ buffer[n] = '\0'; // make sure string is null terminated
+ // send data to serial port
+ write(tty_fd, buffer, n);
+ // wait for data to be sent
+ tcdrain(tty_fd);
+ }
+ toggle_gpio_low();
+ }
+
+ if (FD_ISSET(tty_fd, &readfds)) {
+ tcgetattr(master_fd, &tty);
+ tcsetattr(tty_fd, TCSANOW, &tty);
+ n = read(tty_fd, buffer, BUFFER_SIZE - 1);
+ if (n > 0) {
+ buffer[n] = '\0'; 
+ // send data to pseudo terminal
+ write(master_fd, buffer, n);
+ // wait for data to be sent
+ tcdrain(master_fd);
+ }
+ }
+ }
+
+ // close serial port
+ close(master_fd);
+ close(slave_fd);
+
+ return 0;
+}