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--- products:sbc:common:applications:gpio:uart [2022/07/04 22:27]
nick ↷ Links adapted because of a move operation
+++ products:sbc:common:applications:gpio:uart [2023/11/07 05:09] (current)
nick [Enable UART]
@@ Line 3: / Line 3: @@
 ===== Introduction =====
-This document mainly introduces UART. You will learn how to enable UART on 40-Pin Header on Khadas SBC.
+This page introduces the usage of UART on [[products:sbc:common:applications:gpio:40pin-header|40pin-Header]].
+===== UART Information =====
+|           ^  UART       ^ PIN      ^ GPIO Name  ^  DT Overlays Node  ^  Device Node  ^
+^  VIM1/2   |  UART_AO_B  |  15(RX)  |  GPIOAO_5  |  uart4             |  /dev/ttyS4   |
+| :::       | :::         |  16(TX)  |  GPIOAO_4  | :::                | :::           |
+^  VIM3/3L  |  UART_C     |  15(RX)  |  GPIOH_6   |  uart3             |  /dev/ttyS3   |
+| :::       | :::         |  16(TX)  |  GPIOH_7   | :::                | :::           |
+^  VIM4     |  UART_E     |  15(RX)  |  GPIOY_7   |  uart_e            |  /dev/ttyS4   |
+| :::       | :::         |  16(TX)  |  GPIOY_6   | :::                | :::           |
+^  VIM1S    |  UART_C     |  15(RX)  |  GPIOD_3   |  uart_c            |  /dev/ttyS2   |
+| :::       | :::         |  16(TX)  |  GPIOD_2   | :::                | :::           |
 ===== Enable UART =====
-Uart PIN in 40-Pin Header is PIN15 and PIN16. Refer to [[products:sbc:vim4:configurations:device-tree-overlay|Device Tree Overlay]].
+In order to use the UART, you need to enable the UART function via [[products:sbc:common:configurations:device-tree-overlay|Device Tree Overlay]].
-Enable uart node via device tree overlays. Edit ''/boot/env.txt'' to add ''uartX'' to overlays. E.g.
+<tabbox VIM1/2/3/3L/Edge1>
-```sh
+Edit ''/boot/env.txt'' to add the uart node to ''overlays'' node if it doesn't exist.
-overlays=uart4 pwm_ao_a pwm_f i2c0
+Take VIM3 as an example to enable ''UART_C'', you need to add ''uart3'' node to ''overlays'' node if it doesn't exist.
+```shell
+overlays=pwm_ao_a pwm_f uart3
 ```
-Reboot to effect.
+After reboot, you will see the UART device node.
-<WRAP info >
+```shell
-  * VIM1/VIM2/VIM4 - uar4
+$ ls /dev/ttyS3
-  * VIM3/VIM3L - uart3
+/dev/ttyS3
-</WRAP>
+```
+<tabbox VIM3 with 5.15 kernel>
+Edit ''/boot/dtb/amlogic/kvim3.dtb.overlay.env'' to add uart node to ''fdt_overlays'' node if it doesn't exist.
+e.g. Enable ''UART_C'', you need to add ''uart3'' to node ''fdt_overlays'' if it doesn't exist.
+```shell
+fdt_overlays=uart3
+```
+After reboot, you will see the UART device node.
+```shell
+$ ls /dev/ttyS3
+/dev/ttyS3
+```
+<tabbox VIM3L with 5.15 kernel>
+Edit ''/boot/dtb/amlogic/kvim3l.dtb.overlay.env'' to add uart node to ''fdt_overlays'' node if it doesn't exist.
+e.g. Enable ''UART_C'', you need to add ''uart3'' to node ''fdt_overlays'' if it doesn't exist.
+```shell
+fdt_overlays=uart3
+```
+After reboot, you will see the UART device node.
+```shell
+$ ls /dev/ttyS3
+/dev/ttyS3
+```
+<tabbox VIM4>
+Edit ''/boot/dtb/amlogic/kvim4.dtb.overlay.env'' to add uart node to ''fdt_overlays'' node if it doesn't exist.
+e.g. Enable ''UART_E'', you need to add ''uart_e'' to node ''fdt_overlays'' if it doesn't exist.
+```shell
+fdt_overlays=uart_e
+```
+After reboot, you will see the UART device node.
+```shell
+$ ls /dev/ttyS4
+/dev/ttyS4
+```
+<tabbox VIM1S>
+Edit ''/boot/dtb/amlogic/kvim1s.dtb.overlay.env'' to add uart node to ''fdt_overlays'' node if it doesn't exist.
+e.g. Enable ''UART_C'', you need to add ''uart_c'' to node ''fdt_overlays'' if it doesn't exist.
+```shell
+fdt_overlays=uart_c
+```
+After reboot, you will see the UART device node.
+```shell
+$ ls /dev/ttyS2
+/dev/ttyS2
+```
+</tabbox>
+===== Demo Source Code =====
+```c uart.c
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <termios.h>
+// set correct serial path
+#define SERIAL_PORT "/dev/ttyS2"
+int main() {
+    int serial_port;
+    struct termios tty;
+    // open
+    serial_port = open(SERIAL_PORT, O_RDWR | O_NOCTTY);
+    if (serial_port < 0) {
+        perror("Error opening serial port");
+        return 1;
+    }
+    // Configuration of serial
+    memset(&tty, 0, sizeof(tty));
+    if (tcgetattr(serial_port, &tty) != 0) {
+        perror("Error getting serial port attributes");
+        close(serial_port);
+        return 1;
+    }
+    cfsetospeed(&tty, B921600); // set correct baud rate
+    cfsetispeed(&tty, B921600);
+    tty.c_cflag |= (CLOCAL | CREAD);
+    tty.c_cflag &= ~PARENB;
+    tty.c_cflag &= ~CSTOPB;
+    tty.c_cflag &= ~CSIZE;
+    tty.c_cflag |= CS8;
+    // write configration to serial
+    if (tcsetattr(serial_port, TCSANOW, &tty) != 0) {
+        perror("Error setting serial port attributes");
+        close(serial_port);
+        return 1;
+    }
+    // loop test
+    while (1) {
+        // receive data
+        char received_data[64];
+        if (read(serial_port, &received_data, sizeof(char)*64)) {
+            // get data
+            printf("Received: %s", received_data);
+        }
+        // Only send "Hello, UART!"
+        char data_to_send[] = "Hello, UART!\n";
+        write(serial_port, data_to_send, strlen(data_to_send));
+        // sleep 100ms
+        usleep(100000);
+    }
+    // close
+    close(serial_port);
+    return 0;
+}
+```
+Compile test code:
+```
+$ gcc uart.c -o uart
+```
+===== Test demonstration =====
+Run ''uart''
+```
+$ ./uart
+```
+After connecting PIN15, PIN16 and GND to PC, open ttyUSBX and input hello
+```
+hello
+Hello, UART!
+```
+Check output data:
+```
+$ ./uart
+Received: hello
+```
-===== Check UART Node =====
+===== Disable UART to Use GPIO =====
-After reboot, you will see the uart device node.
+If you want to use normal GPIO instead of UART, you can remove the UART node in [[products:sbc:common:configurations:device-tree-overlay|Device Tree Overlay]].
-  * VIM1/VIM2/VIM4 - /dev/ttyS4
-  * VIM3/VIM3L - /dev/ttyS3

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