sysfs-gpio.h

#pragma once
#include <stdbool.h>

#ifdef __cplusplus
extern "C" {
#endif

// use one of the gpio_open* functions to initialize this structure and use gpio_close() to clean it up.
struct Gpio {
	int fd;		// of value attribute (gets POLLPRI event when configured edge is detected)
	int pathfd;	// of gpio directory
	char *path;	// of gpio directory
};

#define GPIO_INITIALIZER ((struct Gpio){ -1, -1, NULL })

enum GpioOpenMode {
	GPIO_RDONLY	= 2,  // only gpio_read() allowed
	GPIO_RDWR	= 3,  // both gpio_read() and gpio_write() allowed
};

// NOTE: these are logical values for the gpio.  how these map to signal level (low or high) depends on how the
// gpio has been declared in device-tree.
enum GpioValue {
	GPIO_INACTIVE	= 0,
	GPIO_ACTIVE	= 1,
};

enum GpioEdge {
	GPIO_EDGE_NONE,
	GPIO_EDGE_RISING,
	GPIO_EDGE_FALLING,
	GPIO_EDGE_BOTH,
};


// open gpio, do not change current direction (or value, if output).
// for backwards compatibility, mode 0 and 1 are interpreted as GPIO_RDWR and GPIO_RDONLY respectively.
void gpio_open( struct Gpio *gpio, char const *path, enum GpioOpenMode mode );

// open gpio and initialize as input.
// for backwards compatibility, mode 0 and 1 are interpreted as GPIO_RDONLY and GPIO_RDWR respectively.
void gpio_open_input( struct Gpio *gpio, char const *path, enum GpioEdge event_edge, enum GpioOpenMode mode );

// open gpio and initialize as output.
void gpio_open_output( struct Gpio *gpio, char const *path, enum GpioValue init_value );

// close gpio.  it is safe to call this on a zero-filled struct Gpio.  it is safe to call this more than once.
void gpio_close( struct Gpio *gpio );


// check if gpio is configured as active-low (meaning value is opposite of signal level).
bool gpio_is_active_low( struct Gpio const *gpio );


// get current input value or output value (depending on direction).
enum GpioValue gpio_read( struct Gpio const *gpio );

// set output value.  will fail if direction is not set to output or gpio was opened as input-only.
void gpio_write( struct Gpio const *gpio, enum GpioValue value );


// check gpio direction.
bool gpio_is_output( struct Gpio *const gpio );

// change direction to input.  will fail if gpio is not bidirectional.
void gpio_set_direction_input( struct Gpio const *gpio );

// change direction to output.  will fail if gpio is not bidirectional.
// will also fail if event edge is configured to anything other than GPIO_EDGE_NONE.
void gpio_set_direction_output( struct Gpio const *gpio, enum GpioValue init_value );


// change which edge(s) trigger an event (POLLPRI on gpio->fd).
// will fail if gpio direction is output and event_edge != GPIO_EDGE_NONE.
void gpio_set_event_edge( struct Gpio const *gpio, enum GpioEdge event_edge );

// wait for edge event configured using gpio_set_event_edge.
// timeout has same meaning as for poll().
// returns true if edge event was detected, false on timeout.
//
// this is just a simple wrapper for poll() for the simple use-case of waiting on a single gpio.  for more
// complex use-cases, just use poll(), epoll, or your favorite event loop to receive POLLPRI events on
// gpio->fd for each gpio you want to monitor.
bool gpio_wait_event( struct Gpio const *gpio, int timeout );

#ifdef __cplusplus
}  // extern "C"
#endif