DEC KS10 implementation - was CDC 6600 emulation

Rob Doyle radioengr at
Tue Jun 21 03:18:05 CDT 2016

On 6/20/2016 9:07 PM, ben wrote:
> On 6/20/2016 9:43 PM, Eric Smith wrote:
>> On Mon, Jun 20, 2016 at 9:34 PM, ben <bfranchuk at>
>> wrote:
>>> My other pet-peave is that every thing is point and click wizard
>>>  for any useful modules. Need a rom module or adder module, point
>>>  and click no portable code.
>> I predominantly use Xilinx, and I don't use much point-and-click
>> at all. I do all my HDL editing in emacs, including instantiating
>> any of the Xilinx-provided IP blocks. My main interaction with the
>>  Xilinx software (whether ISE or Vivado) is to click the "generate
>>  bitstream" button.  It's even possible to do that from the command
>>  line or a Makefile, but I haven't bothered.
> Do you use Static or Dynamic ram with the FPGA's? Ben.

Another example -

The KS10 FPGA uses 36-bit wide 166 MHz synchronous static RAM (SSRAM)
for main memory. Main memory is as fast as the "Fast ACs". I didn't
bother to implement cache (why bother?) and the Cache Diagnostic still
whines that things that should not be cached are being cached...

Most good tools can infer about everything from a well written HDL
description. This includes single port and multi-port memory and
includes RAM and ROM. The less tool-specific things that you use, the
more portable your design is.

The only IP block that I regularly use is a phased-locked-loop block.

The DEC KS10 used a lot of asynchronous parts (memory, FIFOs/SILOs,
one-shots, delay lines, RC delays, etc) that don't map very well to
modern components - especially FPGAs. I've elected to redesign circuitry
as necessary to use the FPGA resources. Others have elected to retain
the original design as close as possible and accept the consequences.

The KS10 FPGA is at:

The ALU out of the KS10 FPGA describes a fairly complex circuit
containing memory, registers, multiplexers, shifters, adders, including
an am2901 4-bit slice processor-based ALU all written using generic
Verilog. Also the HDL description has trace tags back to the card,
schematic sheet, and reference designators of the original design - if
you'd like to compare the two.

The KS10 FPGA ALU design can be viewed at:

Regarding simulation - a full Verilog simulation of the DEC RP06 disk
diagnostic (DSRPA) requires about two and a half weeks to complete on my
fastest computer. That's maybe not suprising because that simulates the
entire CPU running the diagnostic program, memory, the unibus adapters,
the RH11 disk controller, the console terminal, and eight RP06 disk
drives. When run on the target FPGA, the DSRPA diagnostic completes in
slightly less than 9 minutes.

doyle (at) cox (dot) net

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