Subject: Re: DNARD Video fix
To: Ignatios Souvatzis <ignatios@cs.uni-bonn.de>
From: Mark Hayter <mdh@sibyte.com>
List: port-arm32
Date: 05/14/1999 09:22:38
I don't have the message, but can explain the situation!

There was a problem with the video chip memory clock not starting (which
causes (a) no video and (b) the machine to hang on the first access to
the video system), thought to be a problem with the early passes of the
chip. Both DEC and IGS (who made the chip) worked on a workaround. We
found that adding the 1M resistor introduced enough instability in the
oscillator feedback path that it started up ok, IGS came up with a
software solution (that involved some strange oscillator
enable/disable/reset dance if I recall correctly). The problem with the
hardware fix was *on some sharks* the added feedback prevented the clock
from locking at its highest frequencies (eg 1152x864 at 16 bpp), so we
recommended removing the resistor and relying on the software fix. The
problem with the software only fix was *on some sharks* the clock failed
to start after a reboot. (The software fix is part of the firmware
patch)

I think the best thing to do if you don't care about the highest
resolutions is to leave the resistor in. If you do care about the high
resolutions then try removing the resistor and see if rebooting (bye at
the OFW for example) works, if it does you can be happy! If not you
could try a larger resistor to try to find a point where both things
work.

Mark