PDP era and a question

From: Chuck McManis <cmcmanis_at_mcmanis.com>
Date: Thu Aug 26 18:14:16 1999

At 04:39 PM 8/26/99 -0600, Clint wrote:
> How many gates is a single chip processor going to use? And how
> expensive is an FPGA that size. Or are large PALs a better choice
> (free tools for AMD/Vantis MACH series, and Altera's entry level
> parts)

I bought something called the "Xilinx Student Edition 1.5" from Amazon.com
its a book/CD combination that includes the complete suite of Xilinx
Foundation tools. The book consists of a series of tutorials that last of
which is building an 8 bit microprocessor. This assumes the XC4005 part
which is a "5K equivalent gates' part. The software will also program a
XC4010 which is a "10K equivalent gates" part. The XC4005 and XC4010 from
Digi-key are (for the slower parts) $26 and $62 dollars respectively. A
PDP-11 is certainly doable in the 4010 part, but I don't know if I could do
it and the 11/70 MMU or if I'd end up using two parts. These parts are
"slow" (50Mhz) which is a hell of a lot faster than a lot of -11's :-)

> What to use for a system. If I use a QBus based system (I have
> several available) what are the timing requirements? Is there
> a doc for this? Or Unibus? Or (my current favorite) Socket-7...

There are online versions of ISA interfaces done in Verilog or VHDL. Doing
a Q-bus interface should be pretty straight forward. The specs are in the
architecture manual.

> What architecture? Microcoded or gates? Microcode requires an
> assembler, but might be quicker in the long run.

Intel sued several people over the alleged use of Pentium microcode,
legally gates would probably be safer, also microcode == memory and memory
eats gates rapidly (even though the Xilinx have some cool features to avoid

> And when its all done, what is it really good for? How many
> "hardware hackers" are interested in building CPU boards, and
> are willing to share the cost of laying out and manufacturing
> PCBs?

Well, once a validated VHDL description of a PDP-11 core is produced,
having that made into an ASIC is fairly straight forward. Even some
universities can do small runs (a couple of wafers). If was truely zero
royalties we might get one of the fab houses to consider putting it on
their "standard custom" list. These guys will "fill out" wafers with other
parts to maximize silicon utilization.

>I will probably make a stab at it, but depending on life, might not
>ever finish...

Sounds like the definition of a hobby to me. :-) I'm going to do a PDP-8 on
my evaluation board, and after that will look at helping out on a PDP-11.

Received on Thu Aug 26 1999 - 18:14:16 BST

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