[Libre-soc-dev] Coloquinte legalizer failure

Luke Kenneth Casson Leighton lkcl at lkcl.net
Sat Dec 5 14:07:57 GMT 2020

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)

if he has to do everything this is significantly sub-optimal.

> As the SRAM block will likely be places manually best to discuss with
> JP how to proceed with this.

ok willdo

> So I assume you will go for usage of Instance in litex code ?
> In which tool do you want to simulate it ?

litex has verilator auto-building built-in.  it *should* just be
simulating sram....

ah you are thinking to have a special (verilog) model of that SRAM
cell and explicitly call it?  litex to code up a migen (not nmigen,
MIGEN) Instance?

and then to find the code where wishbone wrappere are made around
SRAM, and call it specially?

i know _how_ to do that (by cut/pasting a *lot* of litex code) and
migen code, all of which makes me nervous.

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.

when yosys is applied there and the cell is substituted.

does that sound reasonable?


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