[Asterisk-Users] Alternatives to SpanDSP??

[Rich Adamson]

> On April 26, 2005 10:57 am, Eric Wieling aka ManxPower wrote:
> > We have terrible problems sending faxes via the TDM cards.  Not even
> > using SpanDSP.  Just TE110P for the telco side and TDM400P for the fax
> > machine.
> 
> Yes there is a timing issue that crept in somewhere in the last 12-15 months; 
> I believe it's related to the CPU use spiking every few seconds.

I would sort of disagree with the spiking thingie (now). If you modify
the zttest app to provide timing output in terms of seconds and microseconds,
you don't see the spiking impacting those measurements. Rather, you
see 8,192 bytes arriving in something greater then 1.000 seconds on
a very consistent basis.

In my case, that timing is right at 1.02 seconds (about 20,000 microseconds
late), which translates into a missed/slipped frame for about one of fifty
frames. Not cool with spandsp at all, but not noticed for pure voice use.

The design of the card (and asterisk) is 100% oriented around receiving
8,192 bytes from the card every 1.0000 seconds exactly. Any significant 
variation from 1.000 seconds will result in a missed frame (1024 bytes)
sooner or later.

What I've not been able to figure out is "why" the delay. I'm 95% sure
it has more to do with asterisk code (including drivers) then it does
with other system interrupt handlers, interrupt latency, etc. Those
_other_ things certainly can impact it, but there is definitely 
something within asterisk that is directly related to the TDM card 
and its drivers. (Its almost consistent enough to look closer at the
clocking on the TDM itself. That assumes a clock on the TDM card is
responsible for raising the interrupt to the O/S via the pci bus.)