On Tue, Jan 08, 2008 at 11:29:08AM -0800, Steve Edwards
wrote:> I have several servers using ztdummy as the timing source, some CentOS
> 4.x, some CentOS 5.x, some Asterisk 1.2.x, some Asterisk 1.4.x.
>
> "zap show status" differs between the servers:
>
> ZTDUMMY/1 (source: Linux26) 1 UNCONFIGUR 0 0 0
> ZTDUMMY/1 (source: RTC) 1 UNCONFIGUR 0 0 0
> ZTDUMMY/1 1 UNCONFIGUR 0 0 0
>
> Is one better than the other? What is the best timing source for ztdummy
> and what does its "status" look like?
The "source" string to ztdummy was only added in latest versions of
ztdummy. So you can't really tell about the last one.
Linux26 gets an interrupt on every tick of the Linux kernel. It works
reasonably well when the kernel has HZ=1000 (was the only possible
value before 2.6.13. And since that kernel that value is configurable,
and the defualt is 250). Using it on newer kernels normally requires
using a non-distro kernel.
The problem with RTC is that the kernel gives us 1024 ticks per second,
rather than the 1000 we need. On zaptel 1.2 this resulted in pretty bad
quality. In 1.4 a PLL was introduced to make the rate better, IIRC.
As of kernel 2.6.22 you can use high-resolution timers support in the
kernel, which is better. In that case you'll see the source
"HRTimer".
So in short, you're mostly stuck with one supported by your kernel,
unless you want to rebuild it.
For future reference, the README file in the Zaptel sorce distribtion,
or its on-line version at http://zaptel.tzafrir.org.il/ .
--
Tzafrir Cohen
icq#16849755 jabber:tzafrir.cohen at xorcom.com
+972-50-7952406 mailto:tzafrir.cohen at xorcom.com
http://www.xorcom.com iax:guest at local.xorcom.com/tzafrir