[Libre-soc-dev] Coloquinte legalizer failure

Luke Kenneth Casson Leighton lkcl at lkcl.net
Sat Dec 5 15:07:43 GMT 2020

On 12/5/20, Staf Verhaegen <staf at fibraservi.eu> wrote:
> Hash: SHA512
> Luke Kenneth Casson Leighton schreef op za 05-12-2020 om 14:07 [+0000]:
>> On 12/5/20, Staf Verhaegen <
>> staf at fibraservi.eu
>> > wrote:
>> > > however to do even a "dummy" P&R a dummy (phantom) cell that can
>> > > be
>> > > placed is needed, isn't it?
>> >
>> > Yes, but you should be able to design RTL without needing to do
>> > P&R.
>> the whole idea is to help JP, who is overloaded, to eliminate many of
>> the early issues (ones that are related to placing *anything*,
>> regardless of layout, not ones specific to a specific PDK)
> I think it is more efficient to just give RTL and let him handle the
> P&R fully than trying to help him in P&R. I think it will take more
> overhead to stay in sync and finding out what you actually did.
> Put JP in CC so he can shime in if he feels like it.

the issue we have at the moment is interaction and bugs when adding 4x
SRAMs, and moving to 64 bit wishbone.

these i am currently assuming are P&R bugs / misunderstandings that
have nothing to do with the size of the physical SRAM cell

debugging and eliminating these is critical before moving to the phase
that is behind the NDA.

without even a dummy / phantom SRAM P&R cell i cannot help triage
those bugs, and, worse, JP is prohibited to a large extent from
telling us how they got fixed.

>> i would greatly prefer to use the standard sram Instance that verilog
>> expects, and to check that the simulated instance created by
>> *unmodified* verilator, unmodified litex, unmodified migen, has the
>> exact characteristics and size required.
> OK, but then you need to make sure that the litex model matches fully
> with the replaced yosys block model.
> I have Verilog/VHDL simulation models of the SRAM, they could be easily
> translated in litex or nmigen simulation models.

ok that would be brilliant, could you post the locations (or contents,
which ever is easier) on #502?

>> when yosys is applied there and the cell is substituted.
>> does that sound reasonable?
> That could work but don't have enough yosys hacking experience to know
> how easy/difficult it is. I'm afraid you will need to find out by
> actually doing it.


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