opensteno_qmk/docs/internals_gpio_control.md

# GPIO Control

QMK has a GPIO control abstraction layer which is microcontroller agnostic. This is done to allow easy access to pin control across different platforms.

## Functions

The following functions can provide basic control of GPIOs and are found in `quantum/quantum.h`.

|Function              |Description                                                       | Old AVR Examples                               | Old ChibiOS/ARM Examples                        |
|----------------------|------------------------------------------------------------------|------------------------------------------------|-------------------------------------------------|
|`setPinInput(pin)`    |Set pin as input with high impedance (High-Z)                     | `DDRB &= ~(1<<2)`                              | `palSetLineMode(pin, PAL_MODE_INPUT)`           |
|`setPinInputHigh(pin)`|Set pin as input with builtin pull-up resistor                    | `DDRB &= ~(1<<2); PORTB \|= (1<<2)`             | `palSetLineMode(pin, PAL_MODE_INPUT_PULLUP)`    |
|`setPinInputLow(pin)` |Set pin as input with builtin pull-down resistor                  | N/A (Not supported on AVR)                     | `palSetLineMode(pin, PAL_MODE_INPUT_PULLDOWN)`  |
|`setPinOutput(pin)`   |Set pin as output                                                 | `DDRB \|= (1<<2)`                               | `palSetLineMode(pin, PAL_MODE_OUTPUT_PUSHPULL)` |
|`writePinHigh(pin)`   |Set pin level as high, assuming it is an output                   | `PORTB \|= (1<<2)`                              | `palSetLine(pin)`                               |
|`writePinLow(pin)`    |Set pin level as low, assuming it is an output                    | `PORTB &= ~(1<<2)`                             | `palClearLine(pin)`                             |
|`writePin(pin, level)`|Set pin level, assuming it is an output                           | `(level) ? PORTB \|= (1<<2) : PORTB &= ~(1<<2)` | `(level) ? palSetLine(pin) : palClearLine(pin)` |
|`readPin(pin)`        |Returns the level of the pin                                      | `_SFR_IO8(pin >> 4) & _BV(pin & 0xF)`          | `palReadLine(pin)`                              |

## Advanced Settings

Each microcontroller can have multiple advanced settings regarding its GPIO. This abstraction layer does not limit the use of architecture-specific functions. Advanced users should consult the datasheet of their desired device and include any needed libraries. For AVR, the standard avr/io.h library is used; for STM32, the ChibiOS [PAL library](http://chibios.sourceforge.net/docs3/hal/group___p_a_l.html) is used.