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 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

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) 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 the kernel at boot.

     The following device.hints(5) 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), 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>.