Add gpio doc. (#1909)

* Add gpio doc.

docs/en/modules/gpio.md

@@ -0,0 +1,108 @@
+# GPIO Module
+| Since  | Origin / Contributor  | Maintainer  | Source  |
+| :----- | :-------------------- | :---------- | :------ |
+| 2016-11-26 | [Johny Mattsson](https://github.com/jmattsson) | [Johny Mattsson](https://github.com/jmattsson) | [gpio.c](../../../components/modules/gpio.c)|
+
+
+This module provides access to the [GPIO](https://en.wikipedia.org/wiki/General-purpose_input/output) (General Purpose Input/Output) subsystem.
+
+
+## gpio.config()
+Configure GPIO mode for one or more pins.
+
+#### Syntax
+```lua
+gpio.config({
+  gpio=x || {x, y, z},
+  dir=gpio.IN || gpio.OUT || gpio.IN_OUT,
+  opendrain= 0 || 1 -- only applicable to output modes
+  pull= gpio.FLOATING || gpio.PULL_UP || gpio.PULL_DOWN || gpio.PULL_UP_DOWN
+}, ...)
+```
+
+#### Parameters
+List of configuration tables:
+
+- `gpio` one or more (given as list) pins, 0 ~ 33 I/O index
+- `dir` direction, one of
+    - `gpio.IN`
+    - `gpio.OUT`
+    - `gpio.IN_OUT`
+- `opendrain` 1 enables opendrain mode, defaults to 0 if omitted
+- `pull` enable pull-up and -down resistors, one of
+    - `gpio.FLOATING` disables both pull-up and -down
+    - `gpio.PULL_UP` enables pull-up and disables pull-down
+    - `gpio.PULL_DOWN` enables pull-down and disables pull-up
+    - `gpio.PULL_UP_DOWN` enables both pull-up and -down
+
+#### Returns
+`nil`
+
+#### Example
+```lua
+gpio.config( { gpio={19,21}, dir=gpio.OUT }, { gpio=22, dir=gpio.IN, pull=gpio.PULL_UP })
+```
+
+## gpio.read()
+Read digital GPIO pin value.
+
+#### Syntax
+`gpio.read(pin)`
+
+#### Parameters
+`pin` pin to read, 0 ~ 33 I/O index
+
+#### Returns
+0 = low, 1 = high
+
+
+## gpio.trig()
+Establish or clear a callback function to run on interrupt for a GPIO.
+
+#### Syntax
+`gpio.trig(pin, type [, callback])`
+
+#### Parameters
+- `pin` 0 ~ 33 I/O index
+- `type` trigger type, one of
+    - `INTR_UP` for trigger on rising edge
+    - `INTR_DOWN` for trigger on falling edge
+    - `INTR_UP_DOWN` for trigger on both edges
+    - `INTR_LOW` for trigger on low level
+    - `INTR_HIGH` for trigger on high level
+- `callback` optional function to be called when trigger fires, trigger is disabled when omitted. Parameters are:
+    - `pin`
+    - `level`
+
+#### Returns
+`nil`
+
+## gpio.wakeup()
+Configuring wake-from-sleep-on-GPIO-level.
+
+#### Syntax
+`gpio.wakeup(pin, level)`
+
+#### Parameters
+- `pin` 0 ~ 33 I/O index
+- `level` wake-up level, one of
+    - `INTR_NONE` to disable wake-up
+    - `INTR_LOW` for wake-up on low level
+    - `INTR_HIGH` for wake-up on high level
+
+#### Returns
+`nil`
+
+
+## gpio.write()
+Set digital GPIO pin value.
+
+#### Syntax
+`gpio.write(pin, level)`
+
+#### Parameters
+- `pin` pin to write, 0 ~ 33 I/O index
+- `level` `gpio.HIGH` or `gpio.LOW`
+
+#### Returns
+`nil`

mkdocs.yml

@@ -35,6 +35,7 @@ pages:
         - 'bthci':       'en/modules/bthci.md'
         - 'dht':         'en/modules/dht.md'
         - 'file':        'en/modules/file.md'
+        - 'gpio':        'en/modules/gpio.md'
         - 'i2c':         'en/modules/i2c.md'
         - 'node':        'en/modules/node.md'
         - 'ow (1-Wire)': 'en/modules/ow.md'