Re: UDB video modes

Eric Smith (
6 Nov 1996 00:58:30 -0000

"D. Steven Daniel" <>
> What do the jumper settings on the UDB motherboard really control? The
> sync frequency in X is determined by XF86Config. Do the jumpers have any
> effect on the resolution and sync frequencies in text mode (Linux-AXP)?

The jumpers just select what video mode the SRM console firmware tries to
use. It has no direct effect on the hardware. The ARC console, Milo, and
the Linux kernel all ignore the jumpers. The video resolution used by the
ARC console can be changed somewhere in its hardware setup menus, but that
still won't help with Milo or Linux.

> Is there info on the internet regarding the tga chip?

Some time back there was a manual available from
but it doesn't seem to be there any more. I've got a copy but I think I'd
have to get permission from DEC if I wanted to redistribute it.

They're not pushing the 21030 any more; maybe it's been obsoleted.

> Can the text mode sync frequencies be re-programmed? Thanks.

In principle, yes. But the code in the kernel (tga.c) is currently

It's been said that there are only a few choices available for the dot clock.
I wonder whether that is actually true, or whether the SRM console or the SROM
merely program a few fixed selections into the clock synthesizer. It seems
unlikely to me that DEC engineers would really have used a non-programmable
clock synthesizer.

It would be really nice if someone from DEC could arrange to make the UDB
schematics and SROM source code available. After all, since it's discontinued
there's no further commercial value to it, right?

I think by hacking the SROM code that initializes the 21066 internal DRAM
controller, it should be possible to make the UDB handle the funny 12 MB SIMMs
in both pairs of SIMM sockets. Then I could trade SIMMs between my two UDBs
so instead of two 88 MB units I could have one 48 MB unit and one 128 MB unit.
I hate to throw away a pair of otherwise good 12 MB SIMMs to upgrade my UDB
from 88 MB to 128 MB.

I still haven't figured out why there's an OTP 27512 EPROM on the UDB
motherboard (at least on the VX42 model). There are three Flash chips for
the SRM and ARC console firmware, a serial EPROM (the boot SROM) and this
other 27512.


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