[Asterisk-Dev] Using linux RTC with ztdummy

[asterisk at billheckel.com]

Mark-

This timing source actually supplies 1000 Pulses per second.  Since 1024 is off by 1/42.666 it skips 
3 pulses every 128 to match back up so the pulse train looks like this:

41 pulses of 976 us 1 pulse of 1953 us  Total= 41.9921875 ms
42 pulses of 976 us 1 pulse of 1953 us  Total= 42.96875   ms
42 pulses of 976 us 1 pulse of 1953 us  Total= 42.96875   ms

For a grand total of 128 pulses in 127.9296875 ms
Some jitter but it's within 99.9% of correct averaged over 128 ms

Bill


Mark Spencer wrote:
> At 1024 Hz, you're going to experience very frequent slips since it's off
> by 24000 ppm.  By comparision most oscillators are in the 25-50 ppm.
> range.  The USB is a much much better source if you have it, although I
> suppose *something* is better than *nothing*.
> 
> Mark
> 
> On 2 May 2003, Klaus-Peter Junghanns wrote:
> 
> 
>>hi guys,
>>
>>attached you will find a ztdummy replacement that was
>>hacked together from the rtc.c in the linux kernel.
>>it keeps all the rtc features and adds zaptel timing
>>if you set the irq frequency to 1024Hz. see the Makefile...
>>
>>basically:
>>make load
>>does the job
>>
>>regards
>>kapejod
>>
>>--
>>Klaus-Peter Junghanns
>>
>>CEO,CTO
>>Junghanns.NET Internet-Services & Software-Development GmbH
>>Breite Strasse 13 - 12167 Berlin - Germany
>>fon:	+49 30 79705392
>>fax:	+49 30 79705391
>>mobile:	+49 160 7503372
>>email:	kpj at junghanns.net
>>
>>Am Fre, 2003-05-02 um 16.50 schrieb Brancaleoni Matteo:
>>
>>>I was wondering if is possible
>>>to use linux RTC to generate timings
>>>for zaptel , so switching ztdummy from
>>>usb-uhci as timing source to RTC.
>>>
>>>That could allow us to be free from that
>>>usb-uhci thing, and not to have to enable
>>>usb only for that. (ideal condition
>>>for pure VoIP asterisk installations)
>>>
>>>Matteo.
>>>
>>>--
>>>Brancaleoni Matteo <mbrancaleoni at espia.it>
>>>Espia - Emmgi Srl
>>>
>>>_______________________________________________
>>>Asterisk-Dev mailing list
>>>Asterisk-Dev at lists.digium.com
>>>http://lists.digium.com/mailman/listinfo/asterisk-dev
>>
>>
> 
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