[alsa-devel] Complex hw buffer with MMAP_COMPLEX?
Hi!
I'm about to start working on the driver for the new RME MADI FX card with its 194 input and 196 output channels.
I've noticed that the device has a rather uncommon hw buffer layout. Let's stick to the input side for the sake of simplicity:
2ch AES, interleaved 8ch MADI 001-008, interleaved 8ch MADI 009-015, interleaved [..] 8ch MADI 184-192, interleaved
On the output side, there is another stereo pair for headphones.
That is, we're dealing with 25 (or 26 for output) interleaved streams with two or eight channels each.
How could we represent such a layout in ALSA, that is, how are we talking to userspace? Would one create subdevices and rejoin them via plughw? Or use MMAP_COMPLEX and then let every application deal with it on its own? It's certainly not a problem to special-case the MADI FX in jackd1 and jackd2, but OTOH, this would require other ALSA apps to do the same (I'm thinking of proprietary custom code).
I wonder if we could afford to rearrange the buffers in the driver and expose a single non-interleaved buffer to userspace.
WDYT?
TIA
Adrian Knoth wrote:
That is, we're dealing with 25 (or 26 for output) interleaved streams with two or eight channels each.
How could we represent such a layout in ALSA, that is, how are we talking to userspace? Would one create subdevices and rejoin them via plughw?
Is it possible to start/stop the streams independently? If yes, this might be useful.
(And subdevices are usually used for streams that are mixed together.)
Or use MMAP_COMPLEX and then let every application deal with it on its own?
Alsa-lib can automatically convert this. Applications that insist on using hw devices have to deal with it (Jack does).
Regards, Clemens
On Tue, Oct 09, 2012 at 03:49:32PM +0200, Clemens Ladisch wrote:
That is, we're dealing with 25 (or 26 for output) interleaved streams with two or eight channels each.
How could we represent such a layout in ALSA, that is, how are we talking to userspace? Would one create subdevices and rejoin them via plughw?
Is it possible to start/stop the streams independently?
No, there's only a single start/stop call for the entire card.
Or use MMAP_COMPLEX and then let every application deal with it on its own?
Alsa-lib can automatically convert this.
The only remaining question is how to tell alsa-lib about the buffer layout.
AFAIKS, there's not even a single driver that uses MMAP_COMPLEX atm.
Cheers
At Tue, 9 Oct 2012 16:09:11 +0200, Adrian Knoth wrote:
On Tue, Oct 09, 2012 at 03:49:32PM +0200, Clemens Ladisch wrote:
That is, we're dealing with 25 (or 26 for output) interleaved streams with two or eight channels each.
How could we represent such a layout in ALSA, that is, how are we talking to userspace? Would one create subdevices and rejoin them via plughw?
Is it possible to start/stop the streams independently?
No, there's only a single start/stop call for the entire card.
Or use MMAP_COMPLEX and then let every application deal with it on its own?
Alsa-lib can automatically convert this.
The only remaining question is how to tell alsa-lib about the buffer layout.
Pass SNDRV_PCM_INFO_COMPLEX to hw.info bit flags. Then set up the channel_info via PCM ioctl ops.
AFAIKS, there's not even a single driver that uses MMAP_COMPLEX atm.
Right. So far only in alsa-lib plugins.
Takashi
participants (3)
-
Adrian Knoth -
Clemens Ladisch -
Takashi Iwai