[DOCS] Writing a new Arduino documentation about GPIO

docs/source/api/gpio.rst

@@ -1,3 +1,170 @@
 ####
 GPIO
 ####
+
+About
+-----
+
+One of the most used and versatile peripheral in a microcontroller is the GPIO. The GPIO is commonly used to write and read the pin state.
+
+GPIO stands to General Purpose Input Output, and is responsible to control or read the state of a specific pin in the digital world. For example, this peripheral is widely used to create the LED blinking or to read a simple button.
+
+.. note:: There are some GPIOs with special restrictions, and not all GPIOs are accessible through the developemnt board. For more information about it, see the corresponding board pin layout information.
+
+GPIOs Modes
+***********
+
+There are two different modes in the GPIO configuration:
+
+- **Input Mode**
+
+In this mode, the GPIO will receive the digital state from a specific device. This device could be a button or a switch.
+
+- **Output Mode**
+
+For the output mode, the GPIO will change the GPIO digital state to a specific device. You can drive an LED for example.
+
+GPIO API
+--------
+
+Here is the common functions used for the GPIO peripheral.
+
+pinMode
+*******
+
+The ``pinMode`` function is used to define the GPIO operation mode for a specific pin.
+
+.. code-block:: arduino
+
+    void pinMode(uint8_t pin, uint8_t mode);
+
+* ``pin``   defines the GPIO pin number.
+* ``mode``  sets operation mode.
+
+The following modes are supported for the basic `input` and `output`: 
+
+* **INPUT** sets the GPIO as input without pullup or pulldown (high impedance).
+* **OUTPUT** sets the GPIO as output/read mode.
+* **INPUT_PULLDOWN** sets the GPIO as input with the internal pulldown.
+* **INPUT_PULLUP** sets the GPIO as input with the internal pullup.
+
+Internal Pullup and Pulldown
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The ESP32 SoC families supports the internal pullup and pulldown throught a 45kR resistor, that can be enabled when configuring the GPIO mode as ``INPUT`` mode.
+If the pullup or pulldown mode is not defined, the pin will stay in the high impedance mode.
+
+digitalWrite
+*************
+
+The function ``digitalWrite`` sets the state of the selected GPIO to ``HIGH`` or ``LOW``. This function is only used if the ``pinMode`` was configured as ``OUTPUT``.
+
+.. code-block:: arduino
+
+    void digitalWrite(uint8_t pin, uint8_t val);
+
+* ``pin``  defines the GPIO pin number.
+* ``val``  set the output digital state to ``HIGH`` or ``LOW``. 
+
+digitalRead
+***********
+
+To read the state of a given pin configured as ``INPUT``, the function ``digitalRead`` is used.
+
+.. code-block:: arduino
+
+    int digitalRead(uint8_t pin);
+
+* ``pin`` select GPIO
+
+This function will return the logical state of the selected pin as ``HIGH`` or ``LOW``.
+
+Interrupts
+----------
+
+The GPIO peripheral on the ESP32 supports interruptions.
+
+attachInterrupt
+***************
+
+The function ``attachInterruptArg`` is used to attach the interrupt to the defined pin.
+
+.. code-block:: arduino
+
+  attachInterrupt(uint8_t pin, voidFuncPtr handler, int mode);
+
+* ``pin``  defines the GPIO pin number.
+* ``handler``  set the handler function.
+* ``mode``  set the interrupt mode.
+
+Here are the supported interrupt modes:
+
+* **DISABLED**
+* **RISING**
+* **FALLING**
+* **CHANGE**
+* **ONLOW**
+* **ONHIGH**
+* **ONLOW_WE**
+* **ONHIGH_WE**
+
+attachInterruptArg
+******************
+
+The function ``attachInterruptArg`` is used to attach the interrupt to the defined pin using arguments.
+
+.. code-block:: arduino
+
+  attachInterruptArg(uint8_t pin, voidFuncPtrArg handler, void * arg, int mode);
+
+* ``pin``  defines the GPIO pin number.
+* ``handler``  set the handler function.
+* ``arg`` pointer to the interrupt arguments.
+* ``mode``  set the interrupt mode.
+
+detachInterrupt
+***************
+
+To detach the interruption from a specific pin, use the ``detachInterrupt`` function giving the GPIO to be detached.
+
+.. code-block:: arduino
+
+  detachInterrupt(uint8_t pin);
+
+* ``pin``  defines the GPIO pin number.
+
+.. _gpio_example_code:
+
+Example Code
+------------
+
+GPIO Input and Output Modes
+***************************
+
+.. code-block:: arduino
+
+  #define LED    12
+  #define BUTTON 2
+
+  uint8_t stateLED = 0;
+
+    void setup() {
+        pinMode(LED, OUTPUT);
+        pinMode(BUTTON,INPUT_PULLUP);
+    }
+
+    void loop() {
+
+       if(!digitalRead(BUTTON)){ 
+         stateLED = stateLED^1;
+        digitalWrite(LED,stateLED); 
+      }
+    }
+
+GPIO Interrupt
+**************
+
+.. literalinclude:: ../../../libraries/ESP32/examples/GPIO/GPIOInterrupt/GPIOInterrupt.ino
+    :language: arduino
+
+.. _datasheet: https://www.espressif.com/sites/default/files/documentation/esp32_datasheet_en.pdf