[Asterisk-Dev] Re: ZTdummy/RTC and genrtc/rtc

[Tony Mountifield]

In article <1122323811.42e54d6321881 at webmail.ntplx.net>,
 <asterisk at ntplx.net> wrote:
> 
> The RTC patch for ZTdummy works MUCH better than the USB hack before.
> (USB timing cause meetme to be useless after about 5 minutes)

That's good to know - thanks! I ought to point out that the USB was only
used to generate timing under a 2.4 kernel. When using 2.6 kernel, USB
was never used, but instead a hook into the kernel jiffy timer.

It was the inaccuracy of the jiffy timer that prompted me to develop the
RTC patch, since I found the same meetme problems as you did.

> We use debian with kernel 2.6.8 and it loads "genrtc" by default.
> The new RTC version of ZTdummy will not work with the "genrtc" module
> and onlt the "rtc" module. I can unload genrtc and load rtc, then it works.
> 
> I have read that the rtc module is broken for some applications and
> that genrtc should be used. Why won't ztdummy work with genrtc?
> Is rtc really broken?

I found that genrtc does not have the special hooks into the interrupt
service routine that rtc has. It appeared to me that rtc is specific to
the PC architecture, with the MC146818 clock chip, whereas genrtc is
more generic, and primarily applicable to non-PC or non-x86 machines.
I don't know why Debian would prefer genrtc over rtc on PC-type
machines, unless it is just striving for ultra-portability with minimum
changes.

I have no experience with Debian, so if you could describe how to make
it load rtc instead of genrtc, that could be put into the source or a
README file.

> I see a good working ztdummy (or the normal digium hardware that has
> always worked for timing) as a key part of not relying on incoming rtp to
> schedule outgoing packets (at some time in the near future)...
> 
> RTC/ztdummy information, for thoes that have not seen it:
> http://bugs.digium.com/view.php?id=4301

Cheers
Tony
-- 
Tony Mountifield
Work: tony at softins.co.uk - http://www.softins.co.uk
Play: tony at mountifield.org - http://tony.mountifield.org