# `Circuits.GPIO.Backend`
[🔗](https://github.com/elixir-circuits/circuits_gpio/blob/v2.3.0/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.

# `force_close`

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

Force all open handles that reference a GPIO spec to close

# `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() | [Circuits.GPIO.gpio_spec()],
  direction :: Circuits.GPIO.direction(),
  options :: Circuits.GPIO.open_options()
) :: {:ok, Circuits.GPIO.Handle.t()} | {:error, atom()}
```

Open one or more GPIOs

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.

Passing a list of GPIO specs opens them together as a group. `read/1` then
returns a single integer and `write/2` takes one, with the first spec as the
least significant bit. All GPIOs in a group must be on the same controller.

Options:

* `:initial_value` - Set to `0` or `1` (or an integer with one bit per line for
  a group). 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.
* `:drive_mode` - Set to `:push_pull`, `:open_drain`, or `:open_source`.
  `:push_pull` 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*