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This commit creates a sbutton device that uses a single button to create a keyboard driver that returns TAB or ENTER depending how long the user keeps the button pressed. Signed-off-by: Alan C. Assis <acassis@gmail.com>
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41 lines
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==================================
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Single Button Multi Actions Driver
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==================================
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**Single Button (aka SButton)** is an kind of keyboard that uses
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only a single physical button (Switch) in the board. This kind of
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button is used with simple interfaces like those used on 3D Printers
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or other devices where all the user needs is to move to the next
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option and confirm the selection.
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It could be done detecting if the button was pressed for a short
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period of time (i.e. less than 500ms) or long pressed. If it is a
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short press the driver will return **TAB** and if it is a long
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press the driver will return **ENTER**. Using it is possible to
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navigate on those kind of menu.
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**How does it work?**. The driver uses a simple config data (this
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config data is equivalent to the platform data on Linux kernel) to
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map the pin from MCU will be used to register and detect the
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interrupt from this pin physically connected to the button.
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It uses a kind of "polymorphism" in C to allow the driver to get
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access to the functions responsible to attach and enable the
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interrupt and to get the status of the pin.
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See ``include/nuttx/input/sbutton.h``
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and ``boards/arm/stm32/common/src/stm32_sbutton.c`` to understand
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better how it works. But basically the board file (config data)
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creates a struct when the first field (variable) is the config
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struct used the but SButton driver (``drivers/input/sbutton.c``).
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Every time the user presses or releases the key button an interrupt
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is generated. The ISR of this interrupt inside sbutton
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(``sbutton_interrupt()``) calls a workqueue to process it (because
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we cannot spend time inside the ISR processing data, it could
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degradate the performance of the RTOS). All that workqueue
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(``sbutton_worker()``) needs to do it measure the elapsed time
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(ticks) from the moment the key was pressed until the moment it
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was released to decide if it is a "KEY_1" (**TAB**) or a "KEY_2"
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(**ENTER**). Then is call the ``keyboard_event()`` from the
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keyboard upper to send this key stroke to the user application.
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