[Soekris] hardware watchdog again...

Jasper Wallace jasper at pointless.net
Tue Jul 23 02:22:09 UTC 2002


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On Thu, 18 Jul 2002, Soren Kristensen wrote:

> Hi Jasper & Everybody.
>
> Jasper Wallace wrote:
> >
> > I've been pokeing at the watchdog registers using ew/dw in the bios, and i
> > wrote enough of a driver for netbsd to be able to test it[1], but no matter
> > what i try i can't get it to do anything - so has anyone got the watchdog
> > driver to react?
> >
> > I've tried on both a Net4501 and a Net4521...
> >
>
> I've been planning to make a document about it, but never got around to
> it. So here is the quick version:
>
> There is a bug in the AMD ElanSC520 processor rev A1 that indirectly
> affect the Watchdog timer. If the GP bus echo mode is enabled (bit 0 in
> MMCR:0C00, see page 10-2 in the SC520 register set manual), writing to
> the watchdog timer control register (MMCR:0CB0) is blocked.
>
> The net4501 BIOS set the GP echo mode bit to fix another bug in the rev
> A1 chips regarding to a pll noise problem. The recommended fix is to
> read and save the GP echo mode register, clear the echo mode bit (write
> 0), then access the watchdog register, and when done, write back the
> saved GP echo mode value.

ok, that does the trick!

I now have a working hardware watchdog driver.

I'll tidy it a bit tommorow night and post a url.

> Boards using the rev B0 do not have that problem, but due to long
> leadtimes on the ElanSC520 I've been using A1's that I could get from
> different stocks.

Presumable the cpu rev id and stepping (in MMCR:0000) change between Rev A1
and B1?

- -- 
[http://pointless.net/]                                   [0x2ECA0975]
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