In search of qbus WCS...

From: Eric Smith <eric_at_brouhaha.com>
Date: Thu Oct 31 00:53:00 2002

> Does anyone have a WCS (writeable control store) board?

Yes.

> If someone does, I need a dump of the contents of the
> microms of the LSI chipset... I'll be happy to write
> the program to do the dump...

In other words, you'll write a microprogram to dump the microms?
Normal PDP-11 code can't do it, even with a WCS board installed.
The WCS board only allows read/write access to the WCS memory; it
provides no means of accessing the contents of the MICROMs. The
RAM Address Register is the low 10 bits of 177540, and only provides
addressing for the WCS RAM. The WCS memory can only be accessed over
the Qbus while the WCS is disabled (bit 10 of 177540 set to 0). And
while the WCS is disabled, the data path to the microinstruction bus
(MIB) is completely disabled.

I'm not completely convinced that it is even possible to write a
microprogram to dump the MICROMs. There's no obvious instruction
to do it, nor is there a suitable data path in the diagrams.

The only obvious way I know of to read the MICROMs is to remove
them from their socket and wire them up to a microcontroller
programmed to act like the control chip but access the locations
sequentially and log the MIB lines.

> (If you also have the EIS/FIS chip, so much the better)

Got that too. You're probably already aware that the EIS/FIS source
code is supplied with the WCS software package. Which I haven't got
a copy of :-(

Anyhow, if you do in fact have a viable means of reading the MICROM
contents, I'll be glad to help.

The *really* tricky part will be reading the translation array, which
is mask-programmed in the control chip. The translation array can cause
microbranches without an explicit branch microinstruction, so the full
control flow of the microcode will not be entirely obvious from just
a MICROM dump. I've considered trying to write a microcode-level
simulator for the LSI-11, but the translation array seems like it will
be fairly difficult to reverse-engineer, short of decapping the control
chip, taking a photomicrograph, and spending a heck of a lot of time
studying the layout.

Eric
Received on Thu Oct 31 2002 - 00:53:00 GMT