pikvm/pages/gpio.md

GPIO

GPIO (general-purpose input/output) is a series of digital interfaces that can be used to connect relays, LEDs, or sensors. Using GPIO on a Pi-KVM is a feature designed for advanced users, so make sure you understand exactly what it is.

In the case of Pi-KVM, the general term GPIO refers not only to the physical interface of the Raspberry Pi, but also to various plugins (for example, for USB relays) that can also be used transparently by emulating abstract GPIO API.

Configuration

Setting up GPIO is quite complex. The interface is divided into several layers for flexibility. All configuration is performed using a file /etc/kvmd/override.yaml which has the YAML syntax.

• Drivers is the first layer that reflects the hardware that represents the IO ports (standard GPIO of Raspberry Pi, USB relay, and so on). Each driver has a type (a plugin that implements the hardware support) and an unique name. Multiple drivers of the same type can be defined at the same time. For example, you can connect multiple relays and give each one its own name. By default, one driver is configured with the name __gpio__, representing the physical GPIO interface of the Raspberry Pi (type gpio).

  kvmd:
      gpio:
          drivers:
              # This example shows how the __gpio__ driver is defined. You don't need to write it in your configuration.
              __gpio__: # Names that start and end with two underscores are reserved. You don't have to define similar names yourself.
                  type: gpio
                  state_poll: 0.1
  
              # You can define another gpio driver with a different polling interval
              my_gpio:
                  type: gpio
                  state_poll: 1.5
  
              # We have HID relay connected to Pi-KVM
              relay:
                  type: hidrelay
                  device: /dev/hidraw0
  

• Scheme is the second layer that reflects how the various driver ports are configured. Each port has a unique name, mode (input or output), pin number, and refers to the driver that provides it. Two interaction modes are available for outputs: pulse and switch. In pulse mode, the output quickly switches its state to logical 1 and back, and in switch mode, it saves the state that the user set. If no driver is specified for the port in the scheme, then __gpio__ will be used. In addition, when KVMD starts and finishes, all output ports are reset to 0. This can be avoided using the initial parameter.

  kvmd:
      gpio:
          scheme:
              # A certain device sends signals to the RPi and we want the Pi-KVM to display this as an led
              led1:
                  pin: 19
                  mode: input
              led2:
                  pin: 16
                  mode: input
  
              # Two outputs of RPi's GPIO
              button1:
                  pin: 26
                  mode: output
                  switch: false  # Disable switching, only pulse available
              button2:
                  pin: 20
                  mode: output
                  switch: false
  
              relay1:  # Channel 1 of the relay /dev/hidraw0
                  pin: 0  # Numerating starts from 0
                  mode: output  # Relays can't be inputs
                  initial: null  # Don't reset the state to 0 when initializing and terminating KVMD
              relay2:  # Channel 2
                  pin: 1
                  mode: output
                  initial: null
                  pulse:
                      delay: 2 # Default pulse value
                      max_delay: 2  # The pulse interval can be between min_pulse (0.1 by default) and max_pulse=5