[asterisk-bugs] [DAHDI-linux 0013930]: dahdi_dummy does not tick on some systems

[Asterisk Bug Tracker]

A NOTE has been added to this issue. 
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http://bugs.digium.com/view.php?id=13930 
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Reported By:                tzafrir
Assigned To:                sruffell
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Project:                    DAHDI-linux
Issue ID:                   13930
Category:                   dahdi_dummy
Reproducibility:            sometimes
Severity:                   minor
Priority:                   normal
Status:                     ready for testing
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Date Submitted:             2008-11-19 08:34 CST
Last Modified:              2009-03-30 11:24 CDT
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Summary:                    dahdi_dummy does not tick on some systems
Description: 
On some systems dahdi_dummy (or ztdummy, in the case of Zaptel) fails to
"tick" DAHDI and hence DAHDI does not provide a working timing source.

Indications that DAHDI (Zaptel) provides no timing source:

1. dahdi_test (zttest) does not give an error on startup, but hangs.
2. Asterisk >= 1.4.20 fails to start, and gives the ugly "no timing
source" error message:

ERROR[10981]: asterisk.c:3036 main: Asterisk has detected a problem
with your DAHDI configuration and will shutdown for your protection.
You have options:
        1. You only have to compile DAHDI support into Asterisk if you
need it.  One option is to recompile without DAHDI support.
        2. You only have to load DAHDI drivers if you want to take
advantage of DAHDI services.  One option is to unload DAHDI modules if
you don't need them.
        3. If you need DAHDI services, you must correctly configure
DAHDI.

An indication that dahdi_dummy should be the timing source for dahdi could
be:

  lsmod | grep ^dahdi
  dahdi                 231888  1 dahdi_dummy

Or to see that /proc/dahdi/1 is dahdi_dummy and is listed as "MASTER".


I have seen various suggestions on how to solve this. None seems to be a
silver bullet. 
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---------------------------------------------------------------------- 
 (0102398) davidw (reporter) - 2009-03-30 11:24
 http://bugs.digium.com/view.php?id=13930#c102398 
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A couple of things to think about.

I've heard that the RTC doesn't co-exist well with HPET timers
<http://groups.google.co.uk/group/comp.protocols.time.ntp/msg/dc9c9851d4c5aa50>.

The trend with recent Linux kernels is towards tickless timing, i.e. not
to actually run the CTC timer at the nominal rate, but to only interrupt
when the kernel thinks there is work to do.  I think it also rounds times
so as to consolidate multiple events into one interrupt.  I believe it is
optional, but distributors may well default it. 

Issue History 
Date Modified    Username       Field                    Change               
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2009-03-30 11:24 davidw         Note Added: 0102398                          
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