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 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

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 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.

       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 o/s.  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  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.

SEE ALSO

       gpioiic(4), gpioled(4), iicbus(4), gpioctl(8)

HISTORY

       The gpiobus manual page first appeared in FreeBSD 10.0.

AUTHORS

       This manual page was written by Sean Bruno <sbruno@FreeBSD.org>.

Debian                                          November 5, 2013                                         GPIO(4)