---
name: "gpio"
section: "4"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["freebsd", "openbsd"]
url: "https://new.carta.tech/gpio/4"
---

# gpio(4)

GPIO bus system

## NAME

**gpiobus** – GPIO bus system

## SYNOPSIS

To compile these devices into your kernel and use the device hints, place the following lines in your kernel configuration file:

**device gpio** **device gpioiic** **device gpioled**

Additional device entries for the ARM architecture include:

**device a10\_gpio** **device bcm\_gpio** **device imx51\_gpio** **device lpcgpio** **device mv\_gpio** **device ti\_gpio** **device gpio\_avila** **device gpio\_cambria** **device zy7\_gpio** **device pxagpio**

Additional device entries for the MIPS architecture include:

**device ar71xxx\_gpio** **device octeon\_gpio** **device rt305\_gpio**

Additional device entries for the POWERPC architecture include:

**device wiigpio** **device macgpio**

Additional device entries for the RISC-V architecture include:

**device sifive\_gpio**

## DESCRIPTION

The **gpiobus** system provides a simple interface to the GPIO pins that are usually available on embedded architectures and can provide bit banging style devices to the system.

The acronym GPIO means “General-Purpose Input/Output.”

The BUS physically consists of multiple pins that can be configured for input/output, IRQ delivery, SDA/SCL *iicbus* use, etc.

On some embedded architectures (like MIPS), discovery of the bus and configuration of the pins is done via [device.hints(5)](/device.hints/5.md) in the platform's kernel [config(5)](/config/5.md) file.

On some others (like ARM), where [FDT(4)](/FDT/4.md) is used to describe the device tree, the bus discovery is done via the DTS passed to the kernel, being either statically compiled in, or by a variety of ways where the boot loader (or Open Firmware enabled system) passes the DTS blob to the kernel at boot.

On a [device.hints(5)](/device.hints/5.md) based system these hints can be used to configure drivers for devices attached to **gpiobus** pins:

- *hint.driver.unit.at*

  The **gpiobus** where the device is attached. For example, "gpiobus0". *driver* and *unit* are the driver name and the unit number for the device driver.

- *hint.driver.unit.pins*

  This is a bitmask of the pins on the **gpiobus** that are connected to the device. The pins will be allocated to the specified driver instance. Only pins with numbers from 0 to 31 can be specified using this hint.

- *hint.driver.unit.pin\_list*

  This is a list of pin numbers of pins on the **gpiobus** that are connected to the device. The pins will be allocated to the specified driver instance. This is a more user friendly alternative to the *pins* hint. Additionally, this hint allows specifying pin numbers greater than 31. The numbers can be decimal or hexadecimal with 0x prefix. Any non-digit character can be used as a separator. For example, it can be a comma, a slash or a space. The separator can be followed by any number of space characters.

The following [device.hints(5)](/device.hints/5.md) are only provided by the **ar71xx\_gpio** driver:

- *hint.gpio.%d.pinmask*

  This is a bitmask of pins on the GPIO board that we would like to expose for use to the host operating system. To expose pin 0, 4 and 7, use the bitmask of 10010001 converted to the hexadecimal value 0x0091.

- *hint.gpio.%d.pinon*

  This is a bitmask of pins on the GPIO board that will be set to ON at host start. To set pin 2, 5 and 13 to be set ON at boot, use the bitmask of 10000000010010 converted to the hexadecimal value 0x2012.

- *hint.gpio.function\_set*

  - *hint.gpio.function\_clear*

  These are bitmasks of pins that will remap a pin to handle a specific function (USB, UART TX/RX, etc) in the Atheros function registers. This is mainly used to set/clear functions that we need when they are set up or not set up by uBoot.

Simply put, each pin of the GPIO interface is connected to an input/output of some device in a system.

## SEE ALSO

[gpioiic(4)](/gpioiic/4.md), [gpioled(4)](/gpioled/4.md), [iicbus(4)](/iicbus/4.md), [device.hints(5)](/device.hints/5.md), [gpioctl(8)](/gpioctl/8.md)

## HISTORY

The **gpiobus** manual page first appeared in FreeBSD 10.0.

## AUTHORS

This manual page was written by Sean Bruno ⟨*sbruno@FreeBSD.org*⟩.