Unibus disk controller with modern storage

Noel Chiappa jnc at mercury.lcs.mit.edu
Thu Oct 20 15:27:31 CDT 2016

    > From: Paul Koning

    > I'd suggest the Massbus series, they are just about as simple as
    > anything and that's where you find the largest capacities short of MSCP
    > devices. 

If you want to exactly emulate only DEC controllers, yes. (Of course, such a
project should do that, for binary compatability.)

However, as I think I have mentioned before, I'm actually enamoured of taking
a very simple controller like an RP11, which has lots of spare disk address
bits, and defining an 'RP11-E' which maxes out the virtual drive size without
changing _anything_ about the register format other than using unused bits in
the cyclinder address register. That will produce disks with 2^28 blocks, or
2^36 bytes, or 64GB. That's most of a large SD card... :)

Not too useful to those without the ability to tweak drivers, but...  there's
another issue with the older controllers, which is that they only support
18-bit addressing, and for use on QBUS machines, where one would really like
to be able to do DMA to anywhere in the 22-bit space (for Unix, this would be
for swapping, and raw I/O - buffered I/O would be fine with 18 bits). So maybe
an updated version of those old, simple controllers would actually have some
use. (I'd certainly want them for my Unix boxes.)

    > Apart from MSCP, avoid RL emulation also.

Why avoid RL's? Not the greatest controller, I agree, but it is a 'lowest
common denominator' drive for a certain era of gear.

    > From: Toby Thain

    > Isn't Noel working on something related?

I think Dave B gave a pretty good update.

In addition to what he mentioned, I'd like to mention the indicator panels
(like the DEC ones for the RF11, RP11, etc). Dave has designed the new
indicator PCB, and we have a couple of prototype PCB's in hand, stuffed and
working. I think there's a video clip of it doing its thing on the Web page he
pointed to.

Our concept is that we'll be able to drive more than one of these panels, by
connecting them together serially - that way a machine could have, say, both
RK11 and RP11 indicator panels, driven from a single QSIC board. That will
slow down the refresh rate a bit, but our numbers indicate it should still be
acceptably fast.


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