[Soekris] sc1100 TSC bug

[David Zelinsky]

Ted Phelps <phelps at gnusto.com> writes:

> dzpost at dedekind.net writes:
> > I'm confused about the status of the sc1100 TSC timer bug and its
> > workaround.  I just installed linux on my new net4801, with a standard
> > 2.6.18 kernel which I built for the purpose.  Based on what I'd read,
> > I configured scx200_hrt module so it would use the high resolution
> > timer as clock source instead of the TSC.
> 
> You need to configure your device to use the 27MHz time source.  The
> following should be enabled in the kernel menu configuration:
> 
>   Bus Options/NatSemi SCx200 support	             (CONFIG_SCx200)
>   NatSemi SCx200 27MHz High-Resolution Timer Support (CONFIG_SCx200HR_TIMER)

That's what I did.  It creates a module called sc200_hrt.  When I
install the module at boot time, the log files say

  kernel: enabling scx200 high-res timer (1 MHz +0 ppm)
  kernel: TSC appears to be running slowly. Marking it as unstable
  kernel: Time: scx200_hrt clocksource has been installed.

and then the clock starts running at roughly 30 times normal speed!
It won't let me remove the module, so I have to comment it out of
/etc/modules and reboot.  When I do that, the log file says:

  kernel: TSC appears to be running slowly. Marking it as unstable
  kernel: Time: pit clocksource has been installed.

and seems to keep time fairly well (based on watching it for a few
minutes only).  So I guess I'll just leave it that way and see how it
goes.  Hopefully I won't find any other need for the high resolution
timer, since it seems to be broken.

But I would still like to know what "pit" is, and whether this is a
good thing to use for a clock.

-David