Custom Placement of Two-Row Tall Cells

Tool: Detailed Placement

Subcategory: Placement violation

Conversation

harshkhandeparkar

In the OpenFASoC LDO generator, a two-row tall comparator latch is custom placed using the place_cell command in a tcl script.

This used to work in earlier versions of OpenROAD, but recently the CI is failing with the following error:

[ERROR DPL-0017] cannot place instance cmp1.

The custom placement is done before running the detailed_placement command in the detail_place.tcl script. If the detailed_placement command is removed, the following error is returned:

[ERROR DPL-0044] Cell cmp1 with height 8140 is taller than any row.
Error: detail_place.tcl, 26 DPL-0044

Relevant Information:

OpenROAD Version hash: e89829335596b351ce665dcc3b73619c0b191c14
Comparator Latch Cell: LEF / GDS
Custom placement script: custom_place.tcl

Is there a way to place this cell (not as a macro) without placement violations?

cc: @msaligane

rovinski

Have you tried marking the cells as FIXED instead of PLACED?

maliberty

We have recently being doing work related to multi-height cells. The error indicates that the detailed placer is trying to legalize this instance which is sounds like you don't want. FIRM should work for that purpose. Can you provide a test case?

maliberty

Your other option is to provide double height site rows.