I checked out the openlane develop branch a couple hours ago, but still having errors with the

or_opendb.tcl

script erroring out. When I implement my design at the

user_proj_example

level, and run

make

on it from the

caravel/openlane

directory, I'm still getting several

Warning: detailed placement failed on _44889_

messages followed by

Warning: Overlap check failed (136).

followed by the

or_opendb.tcl

fatally erroring out. Are the openlane devs aware of this or should I open an issue on github? Or am I doing something incorrect here?

are you using any hard macros?

No, I'm not using any hard macros.

@Matt Aamold: you simply need to change

CELL_PAD

,

FP_CORE_UTIL

, and

PL_TARGET_DENSITY

. Specially the last two. Here is a note I added to the caravel repo and will be included in the release notes when rc5 is out.

NOTE: rc5 (current openlane develop) and rc4 (current openlane master) are using two different concepts of cell padding. rc4 is modifying the LEF, while rc5 is relying on openroad to handle the cell padding. Also, rc4 is using the standalone version of openDP while rc5 is using the one integrated in the openroad app. This affects the concept of PL_TARGET_DENSITY and while in rc4 it was preferred to have PL_TARGET_DENSITY=(FP_CORE_UTIL-(5~10)/100). Now, in rc5 it is preferred to be PL_TARGET_DENSITY=(FP_CORE_UTIL+(1~5)/100). FP_CORE_UTIL should be relaxed as well as it became more representative of the actual core utilization, which wasn't so much the case earlier. So, the perception of these two variables as well as CELL_PAD changed between rc4 and rc5 which necessitates a change in the configurations of almost every single design. CELL_PAD should be 4~6 for the skywater libraries in rc5 unlike rc4 which was 8.This will be included in the release notes when rc5 is released as well as the openlane wiki.

@Amr Gouhar Ok thanks. I was already specifying

PL_TARGET_DENSITY

with a value of

.15

, but I wasn't specifying either

CELL_PAD

or

FP_CORE_UTIL

. I've been able to get past the fatal error from

or_opendb.tcl

by specifying

CELL_PAD

to

4

and

FP_CORE_UTIL

to

20

. I'm getting a fatal error during fastroute now, but I'll leave that as a different thread. I'd like to understand what the deficiency was when not specifying

CELL_PAD

or

FP_CORE_UTIL

(i.e., what their default values were) so I can tune these values better. Are there "typical" values for

FP_CORE_UTIL

?

@Matt Aamold: Usually, the more cells in your design, the more likely that it would get congested, the less you need to set

FP_CORE_UTIL

.

CELL_PAD

is std_cell specific thing to keep a space around the cell to easily access the pins while routing (so the higher the

CELL_PAD

the less the actual utilization). Typically for rc5/develop

CELL_PAD

for the skywater libraries should be 4~6. I think you might find this useful as well. Most of the time the solution to all congestion and failed placement errors is to reduce the

FP_CORE_UTIL

and then change

PL_TARGET_DENSITY

to reflect that. https://github.com/efabless/openlane/blob/develop/regression_results/benchmark_results/SW_HD.csv This sheet, should give you a sense of what to set FP_CORE_UTIL and PL_TARGET_DENSITY for a specific design based on its proximity in the cell count to any of these 40 designs.