# RT-Thread GPIO
[](https://hackmd.io/@ATKTC/S1vO3eXco)

Author : Christpher Kwan ([e-mail])
## What is GPIO ?
* The link below is about some concepts related to GPIO
[](https://hackmd.io/@ATKTC/BygTkzV0yo)

## How to configure GPIO ?
### Useful links
* **Board Schematic**:
* old domain : https://gitlab.hkustracing.com/chleeay/internal_board
* new domain (use this): https://smartcargl.ddns.net/chleeay/internal_board
* **Core Board**: https://drive.google.com/file/d/1W4W5Dwfp7e8sE6FGIGpkS1ixEExaXQ-G/view?usp=sharing

### Important steps
1. First, find an *unused* pin from the **board schematic**
* 
* Let says I choose `P2_FlexSPI_CLK_B` number 15 in this example
2. Second, check the pin name to get the corresponding GPIO port and pins from **Core Board** (start from p.16)
* 
* Since I choose `P2_FlexSPI_CLK_B` number 15, the correspnding GPIO will be `GPIO3_IO4`
* Then, it will be GPIO port3 and pin4
3. Third, define a Marco the GPIO

    /* GPIO3_IO04 */
    #define IR_SENSOR_PIN1            GET_PIN(3,4)

4. Next, set the `pinMode`

    /* set IR_SENSOR_PIN1 pin mode to input */
    rt_pin_mode(IR_SENSOR_PIN1, PIN_MODE_INPUT);

* Check out `pin.h` for the second paramter of `rt_pin_mode`

    /* pin.h */
    #define PIN_LOW                 0x00
    #define PIN_HIGH                0x01

    #define PIN_MODE_OUTPUT         0x00
    #define PIN_MODE_INPUT          0x01
    #define PIN_MODE_INPUT_PULLUP   0x02
    #define PIN_MODE_INPUT_PULLDOWN 0x03
    #define PIN_MODE_OUTPUT_OD      0x04

* Choose the right one according to the hardware design`

## How to write or set GPIO ?
### Read GPIO

int sensor1 =  rt_pin_read(IR_SENSOR_PIN1);

* return values:
* `PIN_LOW` or `PIN_HIGH`
* [API](https://www.rt-thread.io/document/site/programming-manual/device/pin/pin/#read-pin-level)
### Set GPIO
* `rt_pin_write(LED0_PIN, PIN_HIGH);`
* [API](https://www.rt-thread.io/document/site/programming-manual/device/pin/pin/#set-the-pin-level)

## Examples
### Read GPIO

#include <rtdevice.h>
#include <rtthread.h>
#include "drv_gpio.h"

/* GPIO3_IO04 */
#define IR_SENSOR_PIN1            GET_PIN(3,4)

int main(void)
{
    /* set IR_SENSOR_PIN1 pin mode to input */
    rt_pin_mode(IR_SENSOR_PIN1, PIN_MODE_INPUT);
    
    rt_uint8_t sensor1 =  rt_pin_read(IR_SENSOR_PIN1);
    
    char *message = (sensor1 == PIN_HIGH) ? "HIGH" : "LOW";
    rt_kprintf("IR Sensor reads %s.\n", message);
}

### Set GPIO for on-board LED
* default example

#include <rtdevice.h>
#include <rtthread.h>
#include "drv_gpio.h"

/* GPIO1_IO09 */
#define LED0_PIN               GET_PIN(1,9)

int main(void)
{
    /* set LED0 pin mode to output */
    rt_pin_mode(LED0_PIN, PIN_MODE_OUTPUT);
    
    while (1)
    {
        rt_pin_write(LED0_PIN, PIN_HIGH);
        rt_thread_mdelay(500);
        rt_pin_write(LED0_PIN, PIN_LOW);
        rt_thread_mdelay(500);
    }
}

## Further reading:
* https://www.rt-thread.io/document/site/programming-manual/device/pin/pin/#read-pin-level