Re: [Jack-Devel] A couple of related issues in jackd on ARM

On Wed, January 9, 2013 6:13 am, MONTANARO Luciano (MM) wrote:
> Hi all again,
> I am having new problems with jackd2, after our embedded platform switched
> to the 3.1 kernel.
> Actually, I think they were present with our previous kernel as well, but
> they have become systematic while once they were sporadic.
>
> I think I have found the problematic code, but I need some insight from
> someone that knows the code.
> The first problem I am seeing is a very high number of xrun notifications,
> tens of them a second.

You can use -s, --softmode  to disable xrun reporting


> They is due to alsa_driver_wait() returning with 0 as its frame number,
> which normally means an xrun has occurred, but in this case what seems to
> be happening is that jack_wait returns "normally", but with a
> capture_avail of 0 and a playback_avail of 512 on 9 calls out of 10. The
> tenth call I get both capture_avail and playback_avail set to 512. The
> wait_status is set to 0, as in "everything normal", I guess, and so I
> tried to modify JackAlsaDriver to skip the notification in this case, and
> things seem to be working fine, no noticeable glitches in the audio
> playback at all.
>
> The second problem I was referring to is that this high number of
> notifications is triggering a problem in the JackRequest code:
> The CheckRes() macro checks for errors from the Read/Write calls, but
> these calls may silently fail: they can return without writing or reading,
> and this is accounted as success, but then Read() may return uninitialized
> data or Write is not retried when it should.
>
> There is code like this:
>
>          CheckRes(JackRequest::Write(trans));
>          CheckRes(trans->Write(&fName, sizeof(fName)));
>          CheckRes(trans->Write(&fProtocol, sizeof(int)));
>          CheckRes(trans->Write(&fOptions, sizeof(int)));
>          CheckRes(trans->Write(&fUUID, sizeof(int)));
>
> Where I think after each Write there is potential for a needed retry,
> which is not done at all. Am I missing something?
>
> I am using Jackd2 1.9.8, but the affected code has changed little in the
> latest git revisions.
>
> Thanks in advance for your support,
>
> Regards,
> Luciano Montanaro
>
>
> ====
> a38ecd0f049af3b809c5444f66186cdb25ed52fe
>  dist/jackd2/src/linux/alsa/JackAlsaDriver.cpp |    6 ++++--
>  1 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/dist/jackd2/src/linux/alsa/JackAlsaDriver.cpp
> b/dist/jackd2/src/linux/alsa/JackAlsaDriver.cpp
> index a79772f..effb8dd 100644
> --- a/dist/jackd2/src/linux/alsa/JackAlsaDriver.cpp
> +++ b/dist/jackd2/src/linux/alsa/JackAlsaDriver.cpp
> @@ -387,8 +387,10 @@ retry:
>          /* we detected an xrun and restarted: notify
>           * clients about the delay.
>           */
> -        jack_log("ALSA XRun wait_status = %d", wait_status);
> -        NotifyXRun(fBeginDateUst, fDelayedUsecs);
> +       if (wait_status != 0) {
> +            jack_log("ALSA XRun wait_status = %d", wait_status);
> +            NotifyXRun(fBeginDateUst, fDelayedUsecs);
> +       }
>          goto retry; /* recoverable error*/
>      }
>
>
>
> --
> Luciano Montanaro
> EntryNAV - Audio Software Integrator
> Magneti Marelli Electronic Systems
> Viale Carlo Emanuele II 150, Venaria Reale (To)
>
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Patrick Shirkey
Boost Hardware Ltd

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