GPIO - user version

Let's throw away the useless theories and focus on how to use it

GPIO are simply the pins/wires on the MCU (CPU of your robot)

We call the pins

PA0, PA1, PA2, ... , PA16, 
PB0, PB1, ...      , PB16, 
PC0, ...           , PC16, 
..., 
PI0, ...           , PI16

Remember to ask your HW which pins they plug their wires in

GPIO Pins can be set for Input or Output

• Input examples:

  • buttons

  • toggle switch

  • digital line sensors (that only returns white and black)

• Output examples:

  • LEDs (On/Off)

  • Pneumatic cylinders (extend/retract)

Initialization of GPIO

We need to tell the MCU whether we use it for input/output

TODO : how to setup the GPIO pins on .ioc file on CubeIDE

// By default, this line of code is already in your main.c
// It initializes all GPIO that you set up in the .ioc file
MX_GPIO_Init();

GPIO for Input

/* main.h */
#define gpio_read(gpio) HAL_GPIO_ReadPin(gpio##_GPIO_Port, gpio##_Pin)

// usage
uint8_t state = gpio_read(BTN1);

Don't ask why, your HW teammate might make the circuit "0 for Pressed and 1 for Released" so you never know which is Pressed and which is Released until you try it yourself.

More Readability:

Writing gpio_read(BTN1) is also not very readable because you don't know if gpio_read(BTN1) == 1 is pressed or gpio_read(BTN1) == 0is pressed.

So, we defined some more macro functions in main.h for more readability:

/* main.h */
#define btn_read(btn) gpio_read(btn)

If one day your hardware groupmate accidentally swapped the wires of buttons, you can simply change the defines above. You don't need to read through your hundreds/thousands of lines of code and change every gpio_read() you wrote.

GPIO for Output

Writing GPIO Output in the Program

The following macros can be found in main.h

• The gpio_set(gpio) macro sets the GPIO pin to be 1.

• The gpio_reset(gpio) macro resets the GPIO pin to 0.

• The gpio_toggle(gpio) macro toggles the GPIO pin. (i.e. changes the GPIO pin state to 1 if it was originally 0 and vice versa)

Don't ask why, your HW teammate might make the circuit "0 for On and 1 for Off" so you never know which is On and which is Off until you try it yourself.

Examples:

/* main.h */
#define gpio_set(gpio) HAL_GPIO_WritePin(gpio##_GPIO_Port, gpio##_Pin, GPIO_PIN_SET)
#define gpio_reset(gpio) HAL_GPIO_WritePin(gpio##_GPIO_Port, gpio##_Pin, GPIO_PIN_RESET)
#define gpio_toggle(gpio) HAL_GPIO_TogglePin(gpio##_GPIO_Port, gpio##_Pin)

// usage
// Turns off the LED
gpio_set(LED1);

// Turns on the LED
gpio_reset(LED1);

// Toggles the LED
gpio_toggle(LED1);

Full Example (Flickering the LED1 for every 500 ticks)

/* main.c */
int main(void) {

    HAL_Init();
    SystemClock_Config();
    MX_GPIO_Init();

    volatile uint32_t last_ticks = HAL_GetTick();

    while (1) {

        if (HAL_GetTick() - last_ticks > 500) {
            last_ticks = HAL_GetTick();
            gpio_toggle(LED1); // flickering the LED1
        }
    }
    return 0;
}

More Readability:

Writing gpio_set(LED1) is still not very readable because you don't know if it is turning on/off the LED1.

So, we defined some more macro functions in main.h for more readability:

/* main.h */
#define led_on(led) gpio_reset(led) // notice that reset the pin turns the led on
#define led_off(led) gpio_set(led)
#define led_toggle(led) gpio_toggle(led)

If one day your hardware groupmate accidentally swapped the wires of all LEDs, you can simply change the defines above. You don't need to read through your hundreds/thousands of lines of code and change every gpio_set() gpio_reset() you wrote.