[asterisk-dev] On hook reversals

Mike Jagdis mjagdis at eris-associates.co.uk
Wed Jun 6 05:54:42 MST 2007

On Wed, Jun 06, 2007 at 12:50:09AM +0800, Steve Underwood wrote:
> >You mean ZT_SETPOLARITY? You have to do a ZT_ONHOOKTRANSFER as well if
> >you want reverse polarity transfer on-hook (or go off hook if you want
> >loop). If the SI chipset isn't either off hook or in the on hook
> >transfer state polarity has no meaning. (I think it actually sleeps
> >in some "low power" state)
> >  
> Of course polarity has meaning when the loop is open. The open loop 
> always has 48V one way around or the other. Low power states are for 
> parked calls, when the loop is still closed.
> On Sunday my TDM400P got into a state where I could use ZT_SETPOLARITY 
> quite happily with the loop open. I verified, by measurement with a 
> meter, that the line was indeed reversing when I wanted it too. I was 
> happily playing for hours doing various tests. The next day, after a 
> reboot, I couldn't make it work. Looking in the code it seems to be 
> inhibited.

I mean the control register for the SI3210 only allows for
forward-active, reverse-active, forward-oht, reverse-oht.
The magic numbers and conditionals scattered around the zaptel
drivers are simply mirroring that (in their own inscrutable

My guess is that either the ohtimer managed to wrap or you
managed to write something random to it and it spent the day
happily counting down.


Mike Jagdis                        Web: http://www.eris-associates.co.uk
Eris Associates Limited            Tel: +44 7780 608 368
Reading, England                   Fax: +44 118 926 6974

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