hw pause in USB

[Steve deRosier <derosier@pianodisc.com>]

All,

When I have a USB pcm device attached and I press pause in my application, I get a "burp" of audio out of device.  Un-pausing is fine, but then my MIDI and audio are no longer synced up.  This happens in several different players in our system.  This doesn't happen when using the on-board audio (but we're recommending USB audio devices to some customers since the on-board audio may be somewhat noisy for certain configurations).  BTW, this happens on 6 different USB audio devices from different manufacturers.

When running my player via commandline and pressing pause, I get the following error message out of ALSA lib:

ALSA lib pcm_hw.c:535:(snd_pcm_hw_pause) SNDRV_PCM_IOCTL_PAUSE failed: Function not implemented

I'm guessing that the USB driver doesn't implement pause.

My program implements pause by calling snd_pcm_pause( hPCM, 1 );.

For drill:
# cat /proc/asound/cards
0 [rev50          ]: VIA686A - VIA 82C686A/B rev50
                     VIA 82C686A/B rev50 at 0xdc00, irq 10
1 [Opus7          ]: Serial - Serial midi (uart16550A)
                     Serial midi (uart16550A) at 0x3f8, irq 4 speed 115200 div 1 outs 3 ins 3 adaptor Generic droponfull 1
2 [AN1            ]: USB-Audio - HiFi Link AN1
                     XITEL HiFi Link AN1 at usb-0000:00:07.2-1, full speed
# cat /proc/asound/version
Advanced Linux Sound Architecture Driver Version 1.0.4 (Mon May 17 14:31:44 2004 UTC).
Compiled on Jun 23 2004 for kernel 2.6.7.

So, the questions:
* Is there a better way to implement pause in my client program?  
* Is the USB driver broken?  
* Does a more current USB driver fix this issue?  Yes, I know there are more current alsa releases; I ask this because upgrading and qualifying a new kernel and alsa lib on our device is not a trivial undertaking and if a more current USB driver doesn't absolutely fix it then I've got a serious time issue on my hands.
* Can anybody suggest any other workarounds?

Thanks,
- Steve


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