[LAU] GPIO to alsa

[Raphaël Mouneyres]

> Such a software would have to vary according to the keyboard model, the
> available GPIO ports and the extra electronic components used (e.g.
> shift registers or de-multiplexers).

Most keyboards are arranged in a matrix fashion so they have about 16 wires for a 64 notes keyboard.
this may already bee too much for a raspberry, so using a multiplexer is probably mandatory.

> A general purpose operating system like Linux is not best suited for
> such an application, since the scanning rate should be in the
> sub-millisecond range to get a good velocity resolution (assuming you
> have a keyboard with two contacts per key).
> 
> A project that generally does what you want is midibox.

Yes, i have built several midiboxes and also arduino alikes, so very familiar with this easy and efficient way to do midi thing.
I mentioned I would like to avoid extra boards and use ressources existing on the cpu board.
A few multiplexer chips are still easier/cheaper than any midiboard.

As you say, the sub-millisecond timing for the keyboard scanning is important, so if it is not doable in-the-box, even with some real-time kernel and associated module, i would certainly go with those solutions.

Raphaël