Re: [Line6linux-devel] Impulse response test

[Markus G. <gr...@ic...>]

Am Donnerstag, 29. November 2012, 21:18:11 schrieb Stefan Hajnoczi:
> I noticed the qtbased svn branch has a userspace signal generator
> tool.  Does this mean we can drop the impulse response test in the
> driver?
No, the signal generator is not related to the impulse response feature.

> The Kconfig entry notes that doing the impulse response test inside
> the kernel avoids buffering/latency issues but it's not clear to me
> that this code really needs to be in the kernel.  If a userspace
> impulse response test application uses the same buffer size as the PCM
> USB traffic, then it should be just as good?
This is not possible with a PCM API at least for the PODxt since subsequent 
packages in the stream vary in size, i.e., whatever buffer size you choose in 
your application (and when using jackd, it even has to be a power of two), it 
will require splitting or merging some data packages, making the measurement 
unreliable.

It might be possible, though, to get similar results when directly accessing 
the device via libusb (which requires unloading the Line6 driver) in an 
application with realtime privileges. I think this is not highest priority, so 
I propose to leave it as is for now and adress this issue later.

	Kind regards,
		Markus