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

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.
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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