[HECnet] PDP-11/70 on FPGA

[Paul Koning]

On Aug 10, 2010, at 1:09 PM, Brian Hechinger wrote:

On Tue, Aug 10, 2010 at 06:50:32AM -0400, Paul Koning wrote:

http://opencores.org/project,w11
Think that can run RSX/RSTS?
I'll have to take a look... a second reason to get an FPGA eval board...

It only runs on two boards, but at $100 for one, it's not a bad price, really.

I have some other reasons for getting a much higher end (and unfortunately more expensive) board... any changes needed for that should be easy enough.

The larger FPGAs will be able to have main memory on-chip.   That makes the cache unnecessary, though the effort to take it out might not be worth the trouble.

...
Non-MSCP disks can be done in logic; MSCP has always been implemented as firmware running on the storage controller.   Presumably you'd want to do likewise here.   That's certainly possible, with the help of an embedded processor inside the FPGA.   Then you'd have to implement the MSCP firmware, which is a fair chunk of code.   (I don't suppose anyone has the UDA50 firmware available?   Then all you'd need is an FPGA model of the hardware, which would be easy by comparison.)

I *think* I've got a UDA50 laying around (or know someone who does), what would
be required to extract the firmware from it?

Actually, on reconsideration I spoke too fast.   While that would give you a reference for the host end (PDP-11 end) of MSCP, it would also give you lots of extraneous stuff that would only make things harder: Unibus interface machinery, interfacing to the disks and the SI links, etc.

The simpler answer is probably to pick up a disk emulation from one of the emulators, and run that in an embedded CPU inside the FPGA.   Various embedded small processors are readily available; some even come with GCC support.


3) Backend very dependant on some host machine with OS. I guess it helps
to make it doable faster, but for me, the really nice thing would be
something like USB interface to mass storage, which looks like MSCP from
the PDP-11 side. That would be *really* cool.

By far the easiest storage interface is IDE (ATA); is that still around?   Well, it is, in CompactFlash cards... which would do nicely actually.

Yes, I agree, the backend server bothers me a bit as well.   I've love to have
something I could plug a CF card and an ethernet cable into and be done with
it.

CF card interface is just like an old ATA disk; it's quite easy.   Ethernet is a bit harder.   Ethernet cores are available for many FPGAs, either hard dedicated logic (like in the Xilinx Virtex series) or as soft cores.   Come to think of it, some are available on opencores.org.   Eval boards may well come with this, including the necessary VHDL.

And I'll echo what Bob Armstrong said: consider this an opportunity to do some neat hacking.   VHDL is not that hard to learn.   http://www.ashenden.com.au/vhdl-book/DG3E.html is a very good textbook.   (I can't find it on Amazon for some reason, though I'm pretty sure that's where I got it originally...)

	paul