Re: snd_usb_audio

From: Clemens Ladisch (clemens_at_ladisch.de)
Date: 11/16/05

  • Next message: Bernd Petrovitsch: "Re: [2.6 patch] i386: always use 4k stacks" 
    Date:	Wed, 16 Nov 2005 10:11:09 +0100
To: Markus Rechberger <mrechberger@gmail.com>

    Markus Rechberger wrote:
    > finally the em28xx driver made it into the kerneltree, but one
    > problem still remains
    > the snd_usb_audio driver.
    >
    > The problem with the snd_usb_audio driver is that it only supports
    > up to 10 isochronous packets.

    This is packets per URB; we typically have 8 URBs.

    > If people watch TV using such a framegrabber device and set audio
    > to > 8000hz the video isoc transfer will break and the video will
    > stop.

    What exactly breaks? Are you using playback or capture?

    If there is an underrun when starting a _playback_ stream, then it's a
    known bug that has been fixed in 2.6.15-rc1.

    > regarding usbaudio.c (in 2.6.14):
    > #define MAX_PACKS 10
    > #define MAX_PACKS_HS (MAX_PACKS * 8) /* in high speed mode */
    >
    > MAX_PACKS is the upper limit that is adjustable, the second one
    > isn't used at all
    >
    > an easy hack would be to allow up to 100 packets but I also have a
    > usb 1.1 soundblaster that might have problems with too many packets.
    >
    > The correct value for em28xx devices is around 80 packets.

    Did you test this? Capturing doesn't use MAX_PACKS.

    > does anyone know more about the packet limitations on USB 1.1 and
    > 2.0 devices?

    The only limitation are the host controller drivers.

    HTH
    Clemens

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  • Next message: Bernd Petrovitsch: "Re: [2.6 patch] i386: always use 4k stacks"

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