Summary:ASTERISK-05344: 2.6 driver assumes 1000 HZ clock
Reporter:yow (yow)Labels:
Date Opened:2005-10-21 13:55:59Date Closed:2011-06-07 14:02:55
Versions:Frequency of
Description:You just schedule for the next jiffy. That does not ensure that
you will get a 1 kHz timing for ztdummy. The non-dummy drivers
can also be unreliable if you depend on precise timing.

For most architectures, Linux now offers 3 choices:

100 HZ, 250 HZ, 1000 HZ

The default is now 250 HZ, because 1000 HZ is unreliable. The BIOS may
grab the CPU for a long time via the SMI (System Management Interrupt)
and SMM (System Management Mode). While the problem is most common and
severe on laptops, it is also commonly seen on high-end servers.

Basically, you shouldn't rely on a 1 kHz tick working for all hardware.

You especially shouldn't expect this from the system's clock tick.

(BTW, this would have been fixed if the driver shipped with the rest of
the kernel; people regularly scan the source tree for such errors)
Comments:By: Mark Spencer (markster) 2005-10-21 15:12:29

I made ztdummy bomb out if your hz != 1000.  If you want 1000 hz solid, use a zap card.

By: Digium Subversion (svnbot) 2008-06-07 11:05:40

Repository: dahdi
Revision: 796

U   trunk/ztdummy.c

r796 | markster | 2008-06-07 11:05:39 -0500 (Sat, 07 Jun 2008) | 2 lines

Error out on ztdummy if 1000hz is not used (bug ASTERISK-5344)