[LAU] No more PCI!

[Pieter Palmers]

Paul Davis wrote:
> On Fri, Jan 22, 2010 at 3:13 AM, Clemens Ladisch <clemens at ladisch.de> wrote:
>> Firewire devices are currently supported only by FFADO (i.e., only with
>> Jack); I'm writing an ALSA driver for Echo devices right now, based on
>> my AudioFire2.
> 
> uh-oh. no chance we could convince you to instead help Pieter move the
> streaming part of FFADO into the kernel so that it can be used by
> ALSA? Apparently the core part of this has already been done.
> 

Don't worry, we have already been communicating on this. I think its not 
a bad idea to take things one step at a time. The FFADO codebase is not 
really an example of elegance. It bears several signs of a learning 
process, is (therefore) massively over-engineered, and is certainly not 
suitable for kernel space (e.g. is C++, uses floats).

Furthermore the new firewire kernel stack presents an API that is much 
better suited for bi-directional low-latency streaming. The current 
FFADO streaming engine tries to work around the limitations of the old 
stack, but as a result its architecture is not suited for the new 
stack's API.

So a "move" of the streaming part of FFADO degenerates into a re-write 
anyway. And rewriting just what is needed to discover the audiofire is a 
better idea than trying to use FFADO for discovery from the start as the 
audiofire discovery code can be fairly straightforward.

Once an ALSA streaming driver is available for the audiofire, it will 
not be too difficult to adapt it such that it uses FFADO for device 
discovery. This should make it work with all devices that use 
IEC61883/AMDTP streaming (i.e. bebob, dice and oxford based devices). 
I'm already restructuring the FFADO codebase to support an external 
streaming engine. This should make it easy to glue things together once 
the kernel driver is ready.

In any case I'm pretty happy that someone with ALSA experience takes on 
the task of writing a kernel driver, because if I have to do it it would 
probably take another two years.

Greets,

Pieter

PS: An ALSA driver for firewire devices will solve quite some issues 
with respect to user experience and compatibility. Nevertheless I'm 
personally still inclined to maintain and improve the userspace jack 
streaming engine, and also port it to the new firewire stack. I'm not 
convinced that things like hot-plugging, device aggregation and 
sample-accurate midi will be easy to implement using 
jack->ALSA->firewire. So maybe you should worry more about the confusion 
that might cause...