turning down the density doesn't seem to help

I'll copy my answer here as well in case someone missed my answer earlier. Well, that's the thing. rc5 and rc4 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) And 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. CELL_PAD should be 4~6 in rc5 unlike rc4 which was 8. This will be included in the release notes when rc5 is released.

can we get this on the wiki?

@aryap: Sure, I'll add it once rc5 is out.

an anecdote for those stumbling on this: on my design i found that i consistently hit

Please decrease init_density_penalty value

errors for

PL_TARGET_DENSITY

>= 0.138, and

Filler area is negative!!

errors for densities <= 0.134. The fact that I had to even look down to the third decimal place meant it was very easy to miss this when doing regression tests