ANX SDK GPIO API: Digital I/O Control

The ANX SDK GPIO API (anx/gpio.h) lets you configure, read, and write any of the 20 available GPIO pins on the ANX dev module. Whether you are toggling an LED, sampling a button, or bit-banging a custom protocol, every digital I/O operation goes through this API. All functions return anx_err_t so you can handle configuration errors consistently alongside the rest of your application code.

Include

Add the GPIO header to any source file that performs digital I/O operations:

#include "anx/gpio.h"

You still need #include "anx/anx.h" as the first include in your file. anx/gpio.h depends on the common types defined there.

Direction Configuration

Configure a pin as either an input or an output before performing any read or write operations on it. Calling anx_gpio_read() on a pin configured as output, or anx_gpio_write() on a pin configured as input, returns ANX_ERR_INVALID_ARG.

`anx_gpio_set_direction()`

Sets the direction of a GPIO pin.

uint8_t

required

GPIO number in the range 0–33. Refer to the ANX dev module pinout diagram for the physical pin mapping.

dir

anx_gpio_dir_t

required

Pin direction. Use ANX_GPIO_INPUT to configure the pin as a high-impedance input, or ANX_GPIO_OUTPUT to drive it as a push-pull output.

return

anx_err_t

ANX_OK on success. ANX_ERR_INVALID_ARG if pin is out of range or dir is not a valid anx_gpio_dir_t value.

gpio_direction.c

#include "anx/anx.h"
#include "anx/gpio.h"

#define LED_PIN    2
#define BUTTON_PIN 8

void app_main(void) {
    anx_gpio_set_direction(LED_PIN,    ANX_GPIO_OUTPUT);
    anx_gpio_set_direction(BUTTON_PIN, ANX_GPIO_INPUT);
}

Pull Resistor Configuration

Enable an internal pull-up or pull-down resistor on any input pin to avoid leaving it floating. Always call anx_gpio_set_direction() before calling anx_gpio_set_pull().

`anx_gpio_set_pull()`

Configures the internal pull resistor for a GPIO pin.

uint8_t

required

GPIO number in the range 0–33.

pull

anx_gpio_pull_t

required

Pull resistor mode. Choose from:

ANX_GPIO_PULL_NONE — no pull resistor (pin floats when disconnected)
ANX_GPIO_PULL_UP — internal pull-up to VCC
ANX_GPIO_PULL_DOWN — internal pull-down to GND

return

anx_err_t

ANX_OK on success. ANX_ERR_INVALID_ARG if pin is out of range or pull is not a valid value.

Use ANX_GPIO_PULL_UP for active-low buttons and switches. This way the pin reads 1 at rest and transitions to 0 when the button is pressed, which is the expected polarity for falling-edge interrupts.

Reading and Writing

`anx_gpio_write()`

Drives a GPIO output pin high or low.

uint8_t

required

GPIO number in the range 0–33. The pin must already be configured as ANX_GPIO_OUTPUT.

level

uint8_t

required

Output level: 1 to drive the pin high (VCC), 0 to drive it low (GND).

return

anx_err_t

ANX_OK on success. ANX_ERR_INVALID_ARG if the pin is not configured as an output or the pin number is out of range.

`anx_gpio_read()`

Samples the current logic level of a GPIO input pin.

uint8_t

required

GPIO number in the range 0–33. The pin must already be configured as ANX_GPIO_INPUT.

return

uint8_t

1 if the pin is high, 0 if the pin is low. Returns 0 on error (check anx_gpio_set_direction() was called first).

gpio_blink.c

#include "anx/anx.h"
#include "anx/gpio.h"

#define LED_PIN 2

void app_main(void) {
    anx_gpio_set_direction(LED_PIN, ANX_GPIO_OUTPUT);

    while (1) {
        anx_gpio_write(LED_PIN, 1);
        anx_delay_ms(500);
        anx_gpio_write(LED_PIN, 0);
        anx_delay_ms(500);
    }
}

Interrupts

Attach an interrupt handler to a GPIO input pin to react to level changes without polling. ANX OS calls the handler from an interrupt context, so keep the function as short as possible.

`anx_gpio_attach_interrupt()`

Attaches an ISR callback to a GPIO pin.

uint8_t

required

GPIO number in the range 0–33. The pin must already be configured as ANX_GPIO_INPUT.

trigger

anx_gpio_trigger_t

required

The edge or edges that fire the interrupt:

ANX_GPIO_TRIGGER_RISING — fires when the pin transitions from low to high
ANX_GPIO_TRIGGER_FALLING — fires when the pin transitions from high to low
ANX_GPIO_TRIGGER_BOTH — fires on both rising and falling edges

handler

anx_gpio_isr_t

required

A pointer to your ISR callback function. The function signature must be void handler(void *arg).

return

anx_err_t

ANX_OK on success. ANX_ERR_INVALID_ARG if the pin is not configured as input, the pin number is out of range, or handler is NULL.

gpio_interrupt.c

#include "anx/anx.h"
#include "anx/gpio.h"

#define BUTTON_PIN 8

void IRAM_ATTR button_isr(void *arg) {
    // Keep ISR short — just set a flag
    static volatile bool pressed = false;
    pressed = true;
}

void app_main(void) {
    anx_gpio_set_direction(BUTTON_PIN, ANX_GPIO_INPUT);
    anx_gpio_set_pull(BUTTON_PIN, ANX_GPIO_PULL_UP);
    anx_gpio_attach_interrupt(BUTTON_PIN, ANX_GPIO_TRIGGER_FALLING, button_isr);
}

Keep ISR handlers extremely short. Never call anx_delay_ms(), allocate heap memory with malloc(), or invoke any ANX SDK function that is not explicitly marked as ISR-safe inside an interrupt handler. Doing so can corrupt the scheduler state or trigger a watchdog reset. Set a flag in the ISR and handle the work in app_main() or a dedicated task instead.

Debouncing hardware buttons

Mechanical switches produce multiple rapid transitions when pressed or released, causing your ISR to fire several times per button press. The most reliable approach is to record anx_uptime_ms() at the start of the ISR and ignore subsequent interrupts that arrive within 50 ms of the last one. Implement this debounce check in your main-loop handler rather than inside the ISR itself.

​Include

​Direction Configuration

​anx_gpio_set_direction()

​Pull Resistor Configuration

​anx_gpio_set_pull()

​Reading and Writing

​anx_gpio_write()

​anx_gpio_read()

​Interrupts

​anx_gpio_attach_interrupt()

Include

Direction Configuration

`anx_gpio_set_direction()`

Pull Resistor Configuration

`anx_gpio_set_pull()`

Reading and Writing

`anx_gpio_write()`

`anx_gpio_read()`

Interrupts

`anx_gpio_attach_interrupt()`