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

     gpiobus - GPIO 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 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

     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

     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_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.

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

     The gpiobus manual page first appeared in FreeBSD 10.0.

     This manual page was written by Sean Bruno <[email protected]>.

FreeBSD 11.1-RELEASE-p4        November 5, 2013        FreeBSD 11.1-RELEASE-p4
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