GPIO Expander

This firmware allows to configure, read and write all GPIOs over CAN.

Usage

  1. Build and flash

    west build -b ardep -p auto samples/gpio_expander
west flash

  2. Enable can interface

    sudo ip link set can0 type can bitrate 500000
sudo ip link set up can0

    There should be a can interface, linke a USB-CAN adapter connected. The CAN adapter should be connected to the CAN A of the board. Termination should be activated on both ends.

  3. Read pin values

    candump can0

    The frame with 0x003 provides the values of the pins

  4. Confiure pins as output

    cansend can0 001#0F00000000000000

    This configures the first 4 pins as output

  5. Confiure pins as output

cansend can0 001#0800000000000000

This writes a high value to pin 3 and low to 0, 1, 2, if the first 4 pins are configured as output.

Protocol

The order of the pins, depends on the pin definiton in the overlay. Initially all pins are configured as input.

  1. Config frame (client request)

    8 byte: 7 byte config + 1 byte reserved

    bit 0 → Input, bit 1 → Output

  2. GPIO State frame (server update)

    8 byte: 7byte io States, 1 byte reserved

    bit 0 → IO Low, bit 1 → io High

  3. Write GPIOs (client request)

    8 byte: 7byte io States, 1 byte reserved

    bit 0 → IO Low, bit 1 → io High

    Pins not configured as output are ignore, but value might be stored if pin is later configured as output.