Rolf Anderegg wrote:
On 02.11.2011, at 21:19, Clemens Ladisch clemens@ladisch.de wrote:
On the DICE, the playback and capture streams must use a common rate, so I thought I'd avoid handling this in the driver and just use whatever was configured.
Isn't common rate for playback & capture stream often required?
Yes (but not on consumer chips, where it's normal to have independent clocks for all I/Os).
This could be guaranteed by adapting the pcm rate constraints when acquiring one or the other stream.
Yes, and many ALSA drivers already do this. I just wanted to be lazy and put the sample rate selection into a control panel, where other similar settings already have to be handled.
Putting rate and clock selection in the driver also has the benefit of making it mostly usable even without a control panel.
The timing of the stream from the computer to the DICE is synthesized according to the rules in the AMDTP spec (I hope); this was originally written for devices based on the OXFW970 chip. (It's synchronized to the FireWire bus clock.)
This parenthesis is very misleading; what I should have said is that the driver computes the SYT timestamps so that the stream's sample clock is effectively synchronized to the bus clock. These OXFW970-based devices are playback-only and work the same as DICEs with AVS-SYT clock source, i.e., they should also be able to be synchronized to any other device.
ARX1 appears to work fine with my DesktopKonnekt6, but I've never looked at the error counters.
Right, hmm, having scanned the AMDTP (IEC 61883-6) in detail raises some confusion now. Up till now I was under the impression that using AVS-SYT as DICE's clock source is only an option to sync firewire bus slave devices to a clock master device on the same bus.
And this clock master could be either another device that generates SYT timestamps based on its own internal clock, or a computer that just computes the SYTs. (AFAICT the Windows/OSX DICE drivers don't implement the second case. An 'invented' clock isn't useful except for the playback-only devices mentioned above where there just isn't any other clock.)
Regards, Clemens