OK, I uploaded this as a tarball to Jira, as an "improvement" issue type, for the FreeSWITCH project.  Here is a paste of the description that I left there, for everyone's information:

I ran across a problem with a Dahdi-based FreeTDM system a few weeks ago.  Because the timer for mod_conference was not synchronized to the T1 clock source, there was significant periodic on-conference noise.  The problem was not that the "soft" timer was inaccurate; on the contrary, it was a very accurate 1 mS timer in a system that had a pretty inaccurate T1 clock coming in.

My solution was to create a new "mod_dahdi_timer", which derives the ~1 mS timer from 8 ticks of the 8 kHz /dev/dahdi/timer device.  Then a one-line change to mod_conference.c to change "soft" to "dahdi", and the conference sounds perfectly clean.

Installation guidelines:

- Untar the tarball under the freeswitch source directory

- Before ./configure build step, edit modules.conf, adding a line for "timers/mod_dahdi_timer"

- Build as usual

- Add a line to modules.conf.xml enabling mod_dahdi_timer

Testing the timer:

- Only do this if you have a Dahdi T1 board installed and configured with dahdi_cfg.

- "show timers" - verify that the new dahdi timer shows up.

- timer_test 10 10 dahdi

- timer_test 20 10 dahdi

- timer_test 40 10 dahdi

- timer_test 60 10 dahdi

- timer_test 120 10 dahdi

Using the timer:

- Into any config that allows for specifying a timer name, use "dahdi".  This is especially useful for mod_conference.

Todo:

- See TODO comments in mod_dahdi_timer.c .  Exception handling may not be robust, and may fail spectacularly in systems with no configured Dahdi T1 board.

- Comments at the top of mod_dahdi_timer.c may need to be expanded to include the normal FreeSWITCH copyright notices, etc.

On Mon, Oct 21, 2013 at 2:59 PM, Moises Silva <moises.silva@gmail.com> wrote:

On Mon, Oct 21, 2013 at 1:45 PM, Michael Jerris <mike@jerris.com> wrote:

Or for that matter, to put it right in to mod_freetdm.

Agreed, that would be better.

Moy

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_________________________________________________________________________
Professional FreeSWITCH Consulting Services:
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http://www.freeswitchsolutions.com

FreeSWITCH-powered IP PBX: The CudaTel Communication Server
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http://wiki.freeswitch.org
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