GPIO interrupt multiplexer
AVR DA/DB family chips have single interrupt vector for all changes on an I/O port. This poses problem when multiple drivers want to claim the same interrupt (might happen for example with button and discrete joystick drivers using pins on the same port.)
The I/O multiplexer solves it by providing interface similar to irq_attach. However, it allows registration of multiple handlers for the same interrupt vector with additional information recording which pins should be serviced by each handler.
Configuration
The GPIO interrupt multiplexer is enabled in . All basic initialization is done automatically.
Usage
Taking button input driver as an example, this driver requires that the board
provides board_button_irq method which enables and disables servicing
interrupts for given button. Other than ID of the button to be configured,
interrupt handler (function pointer) and opaque argument (void pointer)
parameters are provided.
Instead of calling irq_attach directly, this function may call
avrdx_irq_attach_gpio_mux. Handler and argument are among parameters
of this call but added to that are port index, pins and event that should
trigger the interrupt.
The multiplexer then attaches itself as the interrupt handler for the port. It only runs handlers for pin(s) which triggered the interrupt.
It is possible to have 4 different handlers per port (currently hardcoded.) Handler is considered to be different even if it is the same function but with different opaque argument.
Each handler can have multiple pins assigned to it (provided as a bitmask) but it is not possible to register one pin to multiple handlers.