[Libre-soc-dev] Coloquinte legalizer failure

Luke Kenneth Casson Leighton lkcl at lkcl.net
Fri Dec 4 19:18:09 GMT 2020

On Fri, Dec 4, 2020 at 5:58 PM Jean-Paul Chaput
<Jean-Paul.Chaput at lip6.fr> wrote:

>   This error usually happens when the placer has "too much cells
>   too wide" to place in "too narrow a space". The area is good,
>   but as it obviously can "cut" cells in two, if they are too
>   big it cannot place. Typical case is when there is too much
>   DFFs. As I don't see that effect either I wonder if you are
>   not in the case where a SRAM was synthetized by Yosys as a
>   big bunch of flip-flops...

yes, this would seem to fit.  we know that there is a bug in yosys
where SRAMs are turned into DFFs and try to read multi-megabytes of
0b000000 as initialisation.

this in turn causes cascading overload of abc which i talked to the
developer of abc about, and we realised that what yosys was trying to
do was just... mental.


i honestly have no idea how to "solve" this, there must be some script
modifications to the yosys "synth" command to get it to use ASIC cells
but i just don't know what it is.


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