GPIO(4) FreeBSD Kernel Interfaces Manual GPIO(4)


gpiobusGPIO bus system


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

device gpio
device gpioc
device gpioiic
device gpioled

Additional device entries for the ARM architecure 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 architecure include:

device ar71xxx_gpio
device octeon_gpio
device rt305_gpio

Additional device entries for the POWERPC architecure include:

device wiigpio
device macgpio


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 architechtures (like MIPS), discovery of the bus and configuration of the pins is done via device.hints(5) in the platform's kernel config(5) file.

On some others (like ARM), where FDT(4) 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 kernel at boot.

The following are only provided by the ar71xx_gpio driver.

This is a bitmask of pins on the gpio board that we would like to expose for use to the host o/s. To expose pin 0, 4 and 7, use the bitmask of 10010001 converted to the hexadecimal value 0x0091.
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.
These are a bitmask 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 setup or not setup by uBoot.

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


The gpiobus manual page first appeared in FreeBSD 10.0.


This manual page was written by Sean Bruno <sbruno@FreeBSD.org>.
November 5, 2013 FreeBSD