# `Circuits.GPIO.Backend`
[🔗](https://github.com/elixir-circuits/circuits_gpio/blob/v2.1.3/lib/gpio/backend.ex#L6)

Backends provide the connection to the real or virtual GPIO controllers

# `backend_info`

```elixir
@callback backend_info() :: map()
```

Return information about this backend

# `enumerate`

```elixir
@callback enumerate(options :: Circuits.GPIO.open_options()) :: [
  Circuits.GPIO.identifiers()
]
```

Return a list of GPIOs

See `t:GPIO.identifiers/0` for the information that is returned. The `options` contain
backend-specific options to help with enumeration.

# `identifiers`

```elixir
@callback identifiers(
  gpio_spec :: Circuits.GPIO.gpio_spec(),
  options :: Circuits.GPIO.open_options()
) :: {:ok, Circuits.GPIO.identifiers()} | {:error, atom()}
```

Return identifying information about a GPIO

See `t:gpio_spec/0` for the ways of referring to GPIOs. The `options` contain
backend-specific options to help enumerating GPIOs.

If the GPIO is found, this function returns identifying information about the GPIO.

# `open`

```elixir
@callback open(
  gpio_spec :: Circuits.GPIO.gpio_spec(),
  direction :: Circuits.GPIO.direction(),
  options :: Circuits.GPIO.open_options()
) :: {:ok, Circuits.GPIO.Handle.t()} | {:error, atom()}
```

Open a GPIO

See `t:gpio_spec/0` for the ways of referring to GPIOs. Set `direction` to
either `:input` or `:output`. If opening as an output, then be sure to set
the `:initial_value` option to minimize the time the GPIO is in the default
state.

Options:

* :initial_value - Set to `0` or `1`. Only used for outputs. Defaults to `0`.
* :pull_mode - Set to `:not_set`, `:pullup`, `:pulldown`, or `:none` for an
   input pin. `:not_set` is the default.

Returns `{:ok, handle}` on success.

# `status`

```elixir
@callback status(
  gpio_spec :: Circuits.GPIO.gpio_spec(),
  options :: Circuits.GPIO.open_options()
) :: {:ok, Circuits.GPIO.status()} | {:error, atom()}
```

Return a GPIO's current status

This function returns how a GPIO is configured. The GPIO doesn't need to be
opened. It's different from `gpio_identifiers/2` since it returns dynamic information
whereas `gpio_identifiers/2` only returns information about how to refer to a GPIO
and where it exists in the system.

See `t:gpio_spec/0` for the ways of referring to GPIOs. The `options` contain
backend-specific options to help enumerating GPIOs.

If the GPIO is found, this function returns its status.

---

*Consult [api-reference.md](api-reference.md) for complete listing*