Rich Adamson wrote:
On Fri, 2004-07-16 at 12:07 -0600, Rich Adamson wrote:
No echo on eMachine T2240 2.2ghz Celery, 360m RAM, with either tdm04b
or x100p running any Head cvs after June 23rd (totally stock install).
Wouldn't necessarily recommend this box for any commercial production
use, but...
What's common and not so common between these _very_ diverse boxes?
My guess would be interrupt and/or PCI latency. Echo is produced by
delays in the audio path so if some motherboards are adding delays it's
going to make the echo worse. Fiddling with PCI bus settings both in the
BIOS and from Linux (using the pci tools) may help in some cases.
The unfortunate part about this is that there are SO many variables that
can influence latency that you can't really tell if a motherboard is
going to work or not until you try it. Even two MBs with the same CPUs
and the same north/south bridges could produce different results.
Probably the best we can hope for right now is to start building a
whitelist of known good motherboards for people to reference when
building Asterisk systems.
I'm kinda thinking you're right in the ball park of where 'at least some'
of the remaining echo issues might be coming from. We have an entire
laundry list of what its _not_, but nothing substantial in terms of
what _might_ be causing it on selected systems and no good way to
quantify it.
Frame slips could explain some. All the reports of pages getting chopped
while using the SofFax in spandsp, which I have followed up on, have
been due to frame slips. It seems a lot of people have their clocking
wrong, and those slips willscrew the training of an echo canceller just
as well as they screw up modems.
Anyone have the knowledge/experience to be able to write "something"
that might provide all of us with a clue in terms of buss latency
(or whatever we might want to call this)?
I'm not a programmer, but it would seem like this test app would have to
run in a manner similar to *, interact with digium cards, and return
some value that would represent overall latency. Don't think its all
that important whether it returns an accurate number of milliseconds
or some integer value, as long as the value can be compared from one
motherboard to another (and from one site to another). Sort of a
"run this and tell me what value is returned" kind of thing.
An app that loops back multiple ports and pumps data around in circles
for hours would shake out a lot of flaky systems. I used to use one in
the early days of the Tormenta 1 card, but I probably don't have it any
more.
Regards,
Steve
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