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BREAKING CHANGE: Move the existing STM32 board common sources to boards/arm/common/stm32 and fold in the common STM32F0/L0/G0/C0 board helpers so split STM32 board families can share one source tree. Signed-off-by: raiden00pl <raiden00@railab.me>
72 lines
2.9 KiB
ReStructuredText
72 lines
2.9 KiB
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========================
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MPR121 Capacitive Keypad
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========================
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**What is the MPR121 Keypad**
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The MPR Capacitive Keypad is a small keyboard with 12 keys, similar
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to a telephone keypad, however the keys are numered from 0 to 11.
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This is the picture of the MPR121 Capacitive Keypad:
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.. image:: images/mpr121.png
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:alt: MPR121 Capacitive Keypad
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:align: center
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:width: 200px
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**Purpose**. The MPR121 driver provides a generic keypad
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implementation for this capacitive keypad. The MPR121 uses the I2C
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bus to setup and read the touched/released key and uses an IRQ pin
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(open drain) to indicate when a key is pressed/released or when some
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unnexpected issue happens (currently not used).
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The driver also enables debounce, and emits keyboard events through
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the common keyboard upper-half. This makes the device available as a
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character driver (e.g., ``/dev/keypad0``) using the standard keyboard
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interfaces.
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**Driver Overview**. The MPR121 lower-half scans the matrix and calls
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``keyboard_event()`` when it detects a press or release. The keyboard
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upper-half registers the character device at the requested ``devpath``
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and stores events in a circular buffer. Applications read
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``struct keyboard_event_s`` from the device or use the optional
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kbd-codec layer.
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**Board Support**. To support the MPR121, a board must provide:
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#. **IRQ Definition**
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- Define the GPIO Input pin with pull-up enabled (since the
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IRQ pin is open-drain) to be used to detect the interrupts.
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#. **Registration Hook**
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- Define a ``struct xxx_mpr121config_s`` that will wrap the
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``struct mpr121_config_s config`` as first member and the irq
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argument and ISR handler (xcpt_t isr). The ``config`` needs to
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have its ``.irq_attach`` and ``keymap`` initialized with the
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board IRQ ISR function and the key mapping array.
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- Implement ``board_mpr121_initialize(int devno, int busno)`` to
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call ``mpr121_register(&config, devpath)``. It needs to initialize
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the I2C Master port/channel that will be used to communicate with
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the MPR121 and an instance of that ``xxx_mpr121config_s`` structure.
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- Invoke the board hook during bring-up (for example,
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``board_mpr121_initialize(0, 1)`` for ``/dev/keymap0`` and ``i2c1``).
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**Reference Implementation (STM32F4Discovery)**. The current reference
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is in ``boards/arm/common/stm32/src/stm32_mpr121.c``:
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- Keymap: 4x3 keypad layout
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- Registration: ``board_mpr121_initialize()`` calls
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``mpr121_register()``
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**Data Path Summary**.
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- Board calls ``board_mpr121_initialize(0, 1)``
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- ``mpr121_register()`` initializes and configure the MPR121 chip
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and calls ``keyboard_register(&lower, devpath, buflen)``
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- The upper-half registers the device node at ``devpath``
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- Every time an interruption is generated on IRQ pin it will call the
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``mpr121_worker()`` and it is calls ``keyboard_event()`` on
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press/release of keys.
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- Applications read events from the device node (``/dev/keypad0``).
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