GPIO(4) - Device Drivers Manual #

GPIO(4) - Device Drivers Manual

NAME #

gpio - General Purpose Input/Output

SYNOPSIS #

gpio* at ath? gpio* at bcmgpio? (arm64, armv7) gpio* at glxpcib? (i386) gpio* at gscpcib? (i386) gpio* at isagpio? gpio* at mpfgpio? (riscv64) gpio* at nsclpcsio? gpio* at omgpio? (armv7) gpio* at pcagpio? gpio* at pcaled? gpio* at skgpio? (amd64, i386) gpio* at sxipio? (arm64, armv7) gpio0 at voyager? (loongson)

#include <sys/types.h>
#include <sys/gpio.h>
#include <sys/ioctl.h>

DESCRIPTION #

The gpio device attaches to the GPIO controller and provides a uniform programming interface to its pins.

Each GPIO controller with an attached gpio device has an associated device file under the /dev directory, e.g. /dev/gpio0. Access from userland is performed through ioctl(2) calls on these devices.

The layout of the GPIO device is defined at securelevel 0, i.e. typically during system boot, and cannot be changed later. GPIO pins can be configured and given a symbolic name and device drivers that use GPIO pins can be attached to the gpio device at securelevel 0. All other pins will not be accessible once the runlevel has been raised.

IOCTL INTERFACE #

The following structures and constants are defined in the <sys/gpio.h> header file:

GPIOINFO struct gpio_info

Returns information about the GPIO controller in the gpio_info structure:

struct gpio_info { int gpio_npins; /* total number of pins available */ };

GPIOPINREAD struct gpio_pin_op

Returns the input pin value in the gpio_pin_op structure:

#define GPIOPINMAXNAME 64
struct gpio_pin_op { char gp_name[GPIOPINMAXNAME]; /* pin name */ int gp_pin; /* pin number */ int gp_value; /* value */ };

The gp_name or gp_pin field must be set before calling.

GPIOPINWRITE struct gpio_pin_op

Writes the output value to the pin. The value set in the gp_value field must be either GPIO_PIN_LOW (logical 0) or GPIO_PIN_HIGH (logical 1). On return, the gp_value field contains the old pin state.

GPIOPINTOGGLE struct gpio_pin_op

Toggles the pin output value, i.e. changes it to the opposite. gp_value field is ignored and on return contains the old pin state.

GPIOPINSET struct gpio_pin_set

Changes pin configuration flags with the new ones provided in the gpio_pin_set structure:

#define GPIOPINMAXNAME 64
struct gpio_pin_set { char gp_name[GPIOPINMAXNAME]; /* pin name */ int gp_pin; /* pin number */ int gp_caps; /* pin capabilities (ro) */ int gp_flags; /* pin configuration flags */ char gp_name2[GPIOPINMAXNAME]; /* new name */ };

The gp_flags field is a combination of the following flags:

GPIO_PIN_INPUT

input direction

GPIO_PIN_OUTPUT

output direction

GPIO_PIN_INOUT

bi-directional

GPIO_PIN_OPENDRAIN

open-drain output

GPIO_PIN_PUSHPULL

push-pull output

GPIO_PIN_TRISTATE

output disabled

GPIO_PIN_PULLUP

internal pull-up enabled

GPIO_PIN_PULLDOWN

internal pull-down enabled

GPIO_PIN_INVIN

invert input

GPIO_PIN_INVOUT

invert output

Note that the GPIO controller may not support all of these flags. On return the gp_caps field contains flags that are supported. If no flags are specified, the pin configuration stays unchanged.

Only GPIO pins that have been set using GPIOPINSET will be accessible at securelevels greater than 0.

GPIOPINUNSET struct gpio_pin_set

Unset the specified pin, i.e. clear its name and make it inaccessible at securelevels greater than 0.

GPIOATTACH struct gpio_attach

Attach the device described in the gpio_attach structure on this gpio device.

struct gpio_attach { char ga_dvname[16]; /* device name */ int ga_offset; /* pin number */ u_int32_t ga_mask; /* binary mask */ };

GPIODETACH struct gpio_attach

Detach a device from this gpio device that was previously attached using the GPIOATTACH ioctl(2). The ga_offset and ga_mask fields of the gpio_attach structure are ignored.

FILES #

/dev/gpiou

GPIO device unit u file.

HISTORY #

The gpio device first appeared in OpenBSD 3.6.

AUTHORS #

The gpio driver was written by Alexander Yurchenko <grange@openbsd.org>. Runtime device attachment was added by Marc Balmer <mbalmer@openbsd.org>.

BUGS #

Event capabilities are not supported.

OpenBSD 7.5 - January 17, 2023