[Asterisk-Dev] why not disable clock when using multiple Zaptel cards?

[Steven Critchfield]

On Fri, 2004-11-26 at 13:39 -0500, Andrew Kohlsmith wrote:
> New thread started to prevent thread hijacking:
> 
> On November 26, 2004 12:16 pm, Peter Svensson wrote:
> > There is a field "timing" in /etc/zaptel.conf that ranks incoming spans in
> > the order they are to be considered as a clock source. If all active spans
> > (presumably on a single card) have their timing set to 0 the card and thus
> > all the spans will be clocked from an internal source.
> >
> > Now, given what has been written on the bug tracker and here I suspect
> > there is a bug in ztcfg. It should set up the clocking independently on
> > the two cards. Perhaps it doesn't?
> 
> I have thought about this several times in the past and I'm finally to the 
> point where I can't understand why not.
> 
> If I have a pair of T100Ps, or a TDM400P and a X101P, or any combination of 
> Zaptel cards in a system why on earth does the zaptel driver not disable the 
> timer interrupt for all but one card and use that single timer for clocking 
> everything in the system?
> 
> IIRC there are problems discussed where having two Zaptel cards in a system 
> can cause issues when bridging between them since the timing is off, and 
> using one timer for all Zaptel cards certainly seems like it would be more 
> efficient and eliminate this problem.   Am I missing something obvious?

Maybe because you may be confusing some terminology. For any T1 or E1
interface there is timing on the wire and it is not directly tied to the
IRQs. Timing on the T1/E1 spans are needed to keep them in sync with the
remote end of the line. The interupt is fired after 8 bits of each
channel are prepared. The data needs to be picked up before the next 8
bits are ready. So the timing on the T1/E1 spans needs to be relatively
perfect. The timing of the interupts has some wiggle room. 

As for eliminating the IRQs on any Zap card after the first and letting
the driver handle each and every zap card there after on the same
interupt, sounds interesting, but not all zap cards use the same driver.
T100ps use wct1xxp driver, TDM400P uses wtdm somthing. If they used all
the same drivers it might be possible, otherwise I think there is a
kernel issue with servicing the interupt when your device didn't
generate the interupt.
-- 
Steven Critchfield <critch at basesys.com>