[feat] add linux demo of serial port

linux/main.c

@@ -0,0 +1,45 @@
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <termios.h>
+#include <string.h>
+
+int main() {
+    int fd;
+    struct termios options;
+
+    fd = open("/dev/ttyS3", O_RDWR | O_NOCTTY | O_NDELAY);
+    if (fd == -1) {
+        perror("can not open serial port");
+        return -1;
+    }
+
+    /* config serial port */
+    tcgetattr(fd, &options);
+    options.c_cflag = B115200 | CS8 | CLOCAL | CREAD;
+    options.c_iflag = IGNPAR;
+    options.c_oflag = 0;
+    options.c_lflag = 0;
+    tcflush(fd, TCIFLUSH);
+    tcsetattr(fd, TCSANOW, &options);
+
+    uint8_t buffer_w[] = {0x09, 0x04, 0x00, 0x00, 0x00, 0x20, 0xF0, 0x9A};
+    uint8_t buffer_r[256];
+    while (1) {
+        write(fd, buffer_w, sizeof(buffer_w));
+        sleep(1);
+
+        int num_bytes = read(fd, buffer_r, sizeof(buffer_r));
+        for (int i = 0; i < num_bytes; i++) {
+            printf("%02X ", buffer_r[i]);
+        }
+        printf("\r\n");
+        fflush(stdout);
+    }
+
+    close(fd);
+
+    return 0;
+}