GPIO Usage Overview

In Critical Link kernels we enable GPIO support by default and almost every design will make use of a GPIO for some function (Ethernet reset, status LED, etc.). Please note that the TI Linux GPIO Wiki concerning the GPIO driver is a great resource to reference.

GPIO Pin Muxing

As for all OMAP-L138 pins the pin-mux must be configured in the kernel for every processor pin as each can support different pin-mux modes.

Below are the default GPIO Pin-mux settings for our development board from the arch/arm/mach-davinci/baseboard-industrialio.c file:

* GPIO pins, this is an exhaustive list which may be overridden by
 * other devices
static short baseboard_gpio_pins[] __initdata = {
       DA850_GPIO0_0, DA850_GPIO0_1, DA850_GPIO0_2, DA850_GPIO0_3,
       DA850_GPIO0_4, DA850_GPIO0_5, DA850_GPIO0_6, DA850_GPIO0_7,
       DA850_GPIO0_8, DA850_GPIO0_9, DA850_GPIO0_10, DA850_GPIO0_11,
       DA850_GPIO0_12, DA850_GPIO0_13, DA850_GPIO0_14, DA850_GPIO0_15,
       DA850_GPIO2_12, DA850_GPIO2_15, -1,

GPIO Mapping

The OMAP-L138 processor features up to 144 pins that can be configured as GPIO. They are divided into 9 banks of GPIO's with 16 GPIO's in each.

For example module pin 22 when pin-muxed as a GPIO is GPIO0[6]. That means that to access that GPIO at the Userspace level it is referenced as GPIO# 6. This is based on the 0[6] portion of the GPIO mode name.

0 (GPIO Bank #) * 16 (# of GPIO's per bank) = 0

0 (Base number for bank 0) + 6 (index of this specific GPIO in the bank) = 6.

Example Userspace Usage (for development kit and development kit Kernel)

J701 (50-pin header bottom side) - Pin 19 (Module pin 22 - GPIO0[6])

  1. Login to Linux through the console serial port using the user name of "root" with no password
  2. This will export the GPIO and allow you to use it
    echo "6" > /sys/class/gpio/export
  3. Set the direction as an output
    echo "out" > /sys/class/gpio/gpio6/direction
  4. Set the GPIO - 3.3V driven on this bus
    echo "1" > /sys/class/gpio/gpio6/value
  5. Clear the GPIO - 0V
     echo "0" > /sys/class/gpio/gpio6/value

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