has anyone managed to combine a few big macros with a very s open-source-silicon.dev #openlane

has anyone managed to combine a few big macros wit...

aryap

11/30/2020, 1:03 AM

has anyone managed to combine a few big macros with a very small (~4) number of standard cells? (mostly to drive constants)

aryap

11/30/2020, 1:05 AM

i can't get floorplanning to work because even tweaking

PL_SKIP_INITIAL_PLACEMENT,

PL_BASIC_PLACEMENT

and

PL_RANDOM_GLB_PLACEMENT

, the placer seems impossible to tune correctly. (i tried

PL_TARGET_DENSITY

down to 0.00000377). so i used a custom script to skip initial placement altogether, relying on macro placement and detailed placement. but now of course a lot of stuff overlaps

Hanssel Enrique Morales Norato

11/30/2020, 1:31 AM

I manage to doit by setting the sizing to absolute and setting a fixed area

😮 1

aryap

11/30/2020, 1:32 AM

i've done that 😕

aryap

11/30/2020, 1:32 AM

what density value? how many cells did you have?

Hanssel Enrique Morales Norato

11/30/2020, 1:48 AM

Around 100 cells, I'm trying to run a design that uses 2 DFFRAM, but I'm getting some overlap even when the floorplanning results show that the design it's oversized.

Amr Gouhar

11/30/2020, 4:05 PM

@aryap: Maybe, consider putting these 4 cells in another macro? So, the top level would only contain macros.

aryap

11/30/2020, 7:16 PM

Hmmmmm ok. They’re just constants. Maybe I can avoid them

Amr Gouhar

11/30/2020, 7:28 PM

@aryap: From experience, it's easier to have conb cells wrapped in a macro rather than have them floating around in the top level and causing routing trouble.

aryap

11/30/2020, 8:09 PM

my solution seems to be to re-run the flow until the initial seed places the 4 annoying cells somewhere not problematic

aryap

11/30/2020, 8:09 PM

but i guess the constant macro is next

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