[Oberon] FPGA RISC memory interfacing

[Magnus Karlsson]

Wojtek:

It could be something wrong with that board.
You can send it back for a replacement board if this is a recurring problem.

Magnus

On 12/22/2019 7:22 PM, Skulski, Wojciech wrote:
> Paul:
>
>    thank you for the note. I am facing a practical problem that I would like to use RISC5 and the rest of the FPGA Oberon System in practical situations. The limitation that it only works well with asynch RAM is a serious one. I wonder how easy it will be to convert RISC5 to a synchronous design.
>
> FYI, I am not sure if the present design works well with Pepino whose idea is almost the same as the original Spartan-3 board. It is the same memory connected to Spartan-6 rather than Spartan-3. I noticed that Oberon System frequently freezes on one Pepino which we have. I have not identified any pattern. Sometimes it works for days, and sometimes if freezes after a mouse click on a command like the Hilbert curve. I suspect a timing violation.
>
> Reengineering the CPU may help solve this problem.
>
> Thank you,
> Wojtek
> ________________________________________
> From: Oberon [oberon-bounces at lists.inf.ethz.ch] on behalf of Paul Reed [paulreed at paddedcell.com]
> Sent: Sunday, December 22, 2019 8:56 AM
> To: ETH Oberon and related systems
> Subject: [Oberon] FPGA RISC memory interfacing
>
> Hi Wojtek,
>
>> I want to connect ... to a memory chip ... IS61NLP102418B-200B3L.
>> ... A quick look at the RISC5 code reveals that the state machines seem
>> not be present in this code...So this design is quite interesting.
>> Most of the RISC5 code is combinational...
> Right, it's not a pipelined design.
>
> Also I think the intention is to explain its operation for a general
> audience, not for an electronics designer.  Nevertheless it's pretty
> clear, certainly in comparison with most other designs out there.
>
> To see the effects of the combinational choice, you would need to do
> some more realistic simulation, e.g. post-synthesis, rather than just
> simulating the Verilog source, to see the effects of the actual delays
> in the real hardware, which are very significant.
>
> That ISSI synchronous memory chip would probably work better with a
> pipelined design like RISC-V.  Prof. Wirth's RISC works well with
> asynchronous SRAM, as has already been discussed.
>
> HTH,
> Paul
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