[LAU] strange behaviour with novation launchpad

[Fons Adriaensen]

On Thu, Jul 12, 2012 at 09:24:34PM +0200, Atte André Jensen wrote:

> I'm trying to use my novation launchpad with chuck. It seems to be
> plug/play, at least I didn't do anything except plug and play :-)
> 
> However it's acting a bit strange in one regard. The first time I
> handle (read presses from the launchpad and sends something back to
> turn lights on/off) it works as expected.
> 
> However the next time I launch my chuck code (without turning off =
> unplugging the launchpad) it doesn't send presses. However the arrow
> up, down, left and right buttons (or at least the up-one, that's
> what I got used to use) works and after pressing it the other
> buttons start sending again.
> 
> Every once in a while, it's the other way around, I have to press a
> grid button before the arrow pads start sending.
> 
> I checked my chuck code quite thoroughly, and played with various
> things to remedy the problem, but still it might be something I send
> that messes up the launchpad.
> 
> Can anyone recognize this behavior? Or the opposite: testify that it
> works without this quirk? Any ideas how to approach the problem,
> narrow down the possibilities and hopefully eventually find a fix?

That is because the LP sends MIDI using running status, and there
is no way to reset it (i.e. force a status byte on the next message),
except a power cycle. The top row uses controller events while the
rest uses key up/down. After re-opening the device the driver code
needs a status byte, and usually using the top row will provide one
(assuming the last event in the previous session was a key one).

Actually *most* events are unambiguous even without a status byte,
but you'd need some ad-hoc code in the driver to exploit that.

Ciao,

-- 
FA

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