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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)
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
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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
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aryap

11/30/2020, 1:32 AM
i've done that 😕
what density value? how many cells did you have?
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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.
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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.
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aryap

11/30/2020, 7:16 PM
Hmmmmm ok. They’re just constants. Maybe I can avoid them
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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.
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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
but i guess the constant macro is next