# GPIO
[GPIO (general-purpose input/output)](https://en.wikipedia.org/wiki/General-purpose_input/output) is a series of digital interfaces that can be used to connect relays, LEDs, sensors, and other components.
:exclamation: Note: Using GPIO on a Pi-KVM was designed as a feature for advanced users, so please familiarize yourself with the topic to make sure you understand how to use use it before setting it up. Otherwise you might damage your Raspberry Pi or components.

When talking about Pi-KVM and GPIO it refers not solely to the [physical interface of the Raspberry Pi](https://www.raspberrypi.org/documentation/usage/gpio), but also to various plugins (for example, for [USB relays](http://vusb.wikidot.com/project:driver-less-usb-relays-hid-interface)) that can also be used transparently by emulating an abstract GPIO API.

# Configuration
Setting up GPIO is considerably complex. The interface is divided into several layers for flexibility. Any configuration is performed using a file `/etc/kvmd/override.yaml` which uses the [YAML syntax](https://docs.ansible.com/ansible/latest/reference_appendices/YAMLSyntax.html). We will look at each part of the configuration individually with an example for each.

### Drivers
The first part of the configuration refers to the hardware layer, which defines which IO ports are used (standard GPIO pins of the Raspberry Pi, an USB relay, and so on). 
If you just want to use GPIO with the default settings you can skip to the next section [Scheme](#Scheme)

Each hardware input / output requires a individual driver configuration entry. Each driver has a type (which refers to the plugin that handles the communication between Pi-KVM and the hardware) and a unique name. 
This allows you to either can add multiple drivers of the same type with different settings or connect multiple USB HID relays.

:exclamation: Each driver requires a unique name. Names surrounded by doube underscore are system reserved and should not be used.

The only exception to this is the default GPIO driver with the name `__gpio__`, representing the physical GPIO interface of the Raspberry Pi. The configuration section for `__gpio__` is only required in your `/etc/kvmd/override.yaml` if you want to change the default settings. It can be omitted if you are fine with the defaults.

```yaml
kvmd:
    gpio:
        drivers:
            # This example shows how the default __gpio__ driver settings can be changed. It can be omitted if you are fine with the defaults.
            __gpio__:  # Names surrounded by doube underscore are system reserved
                type: gpio # refers to the plugin name handling the communication
                state_poll: 0.1 # seconds

            # You can define another gpio driver with a different polling interval
            my_gpio: 
                type: gpio # refers to the plugin name handling the communication
                state_poll: 1.5 # seconds
                    
            # Example for a USB HID relay connected to Pi-KVM
            relay:
                type: hidrelay # refers to the plugin name handling the communication
                device: /dev/hidraw0 # the path to the linux device
```

### Scheme
The second part defines how the various driver ports are configured. Each port has a unique name, a mode (`input` or `output`), a pin number, and a reference to the driver configured in the previous part.

Two interaction modes are available for outputs: `pulse` and `switch`. In pulse mode, the output quickly switches its state to logical 1 and back (just like pressing a button). In switch mode, it saves (toggles) the state that the user set. When Pi-KVM is started / rebooted (any time the KVMD daemon is started or stopped) all output ports are reset to 0. This can be avoided using the `initial` parameter.

If you don't specify a driver for the port in the scheme the default driver, `__gpio__` will be used.

|  name                         |   Type      |   Allowed values       |   description                          |
|---                            |---          |---                     |---                                     |
| led1, button1, relay1, etc.   | varchar     | a-Z, numbers, "_", "-" | a name for the port                    |
| pin                           | integer     | integer numbers        | refers to a GPIO pin                   |
| mode | predefined| input or output | defines if a port is used for input or output (Relays can't be inputs)|
| switch | bool | true or false | sets the port to switch (true) or pulse (false) mode.  |
| initial | bool | true, false or null | defines the initial state of the switch upon boot (only usable for USB HID relays |
| pulse | none | - | a section header to define switch pulse configuration  |
| delay | float | positive float values | defines the pulse time in seconds |
| min_delay | float | positive float values | |
| max_delay | float | positive float values | |

__Example configuration__
```yaml
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 # GPIO pin number on the RPi
                mode: input 
            led2:
                pin: 16 # GPIO pin number on the RPi
                mode: input 

            # Two outputs of RPi's GPIO
            button1:
                pin: 26 # GPIO pin number on the RPi
                mode: output
                switch: false  # Disable switching, only pulse available
            button2:
                pin: 20 # GPIO pin number on the RPi
                mode: output
                switch: false # Disable switching, only pulse available

            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 # Relays can't be inputs
                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
```

### View
This is the last part of the required configuration. It defines how the previous driver and port configuration is rendered on the Web interface. Here's an example for the example configuration above:

```yaml
kvmd:
    gpio:
        view:
            header:
                title: Switches  # the menu title
            table:  # The menu items are rendered in the form of a table of text labels and controls
                - ["#Generic GPIO leds"]  # Text starting with the sharp symbol will be a label
                - []  # creates a horizontal separator and starts a new table
                - ["#Test 1:", led1, button1]  # Text label, one input, one button with text "Click"
                - ["#Test 2:", led2, button2]
                - []  # creates a horizontal separator and starts a new table
                - ["#HID Relays /dev/hidraw0"]
                - []  # creates a horizontal separator and starts a new table
                - ["#Relay #1:", "relay1,Boop 0.1"]  # Text label and button with alternative text
                - ["#Relay #2:", "relay2,Boop 2.0"]  # Text label and button with alternative text
```

This will be rendered as:

<img src="../img/gpio_menu.png" alt="drawing" />

Some rules and customization options:
- Text starting with the `#` symbol will be a label.
- To place a port in a cell, use the name you defined in the scheme.
- Inputs are displayed as round LEDs.
- Outputs are displayed as a switch AND a button.
- If the switch mode is disabled, only a button will be displayed. If pulse is disabled, only a switch will be shown.
- To change title of the button, write some its name using comma like `"relay1,My cool relay"`.