30 Dec
2008
30 Dec
'08
12:30 a.m.
On Mon, Dec 29, 2008 at 6:02 PM, Guy Sotomayor <ggs at shiresoft.com> wrote:
If there's enough interest, I'll try for it
since I'm doing a unibus memory
board (a multifunction board) with an FPGA for everything but the memory and
interfaces. I'd have to look at the interface from the cache boards, but I
might be tempted to use SSRAMs since they can be obtained in wide bit widths
(36 bits) in a single chip and aren't too difficult to interface to (timing
wise). I know that they come in 512K x 36 since I'm considering that for
another project. So that would only require 2 parts for the entire memory
array (4MB).
Handy.
If ECC were required, there'd be a bit more
involved and I'd
have to look to see what was available.
My personal thought was that one could get away with simulated ECC
(enough to fool what the OS is expecting) or I do know that one can do
some form of ECC with 36 bits per word - I have an Alpha board that
does it (36-bit-wide 72-pin SIMMs).
However, I'm swamped with my real job and
haven't had a lot of time (read
none) to spend on this stuff.
Understandable.
I've already done the schematic capture for
the Unibus interface and level shifters and I'm about 15-20% done coding up
the verilog for the FPGA. I've done all of the high level design, memory
timing and unibus address decode. The rest is the internal interconnect,
serial, unibus state machine and configuration state machine plus the
individual unibus devices (memory, KW11L, ROMs, 2 SLUs).
Cool.
Speaking only for myself, a modern Unibus board is more interesting
than a board that only works in 11/70s. The number of 11/70s running
in hobbyists' hands is tiny compared to the overall number of lesser
Unibus machines. And since many of those lesser machines might not
have a full load of memory, the impact of changing from old to new is
greater. My 11/70s have full MK11s - the idea of running without an
MK11 is about space (second rack) and power consumption and
maintainability. If I had run across an 11/70 CPU only that had lost
the MK-11 some time back, I might feel differently, but I think the
ratio of 11/70s with no memory to ones that are complete is rather
small.
I look forward to hearing more about, then buying, your universal
memory board. I'm not sure I could afford a modern PEP-70
replacement, let alone two.
-ethan