How to limit max fanout/fanin in synthesis stage with OpenROAD-flow-scripts?

[dearmrlv]

I've checked yosys documentation for tcl command: synth, and I cannot figure out options to limit max fanout/fanin in synthesis. Is it possible to limit max fanout/fanin in synthesis stage with OpenROAD-flow-scripts? How to do it?
Thanks for any suggestions!

[maliberty]

I don't know of a direct way though you might ask the question in https://github.com/YosysHQ/yosys/discussions or their Slack channel. I do believe that the .lib's max cap is obeyed so there is an indirect limit.

[dearmrlv]

OpenROAD-flow-scripts/flow/designs/gf12/coyote/constraint_hier.sdc

Line 2116 in 882dc81

set_max_fanout 10.0000 [current_design]

OpenROAD-flow-scripts/flow/platforms/gf180/config.mk

Line 54 in 882dc81

export MAX_FANOUT = 20

OpenROAD-flow-scripts/flow/platforms/sky130hd/lib/sky130_dummy_io.lib

Line 21 in 882dc81

default_max_fanout : 30;

Hi, Here are what I found about the max fanout issue in ORFS repository. Can these lines work as they expected? Or these lines just have no effect? @maliberty

[maliberty]

You said "in synthesis" and I'm not clear that yosys/abc pick up the SDC constraints. The .lib may well be effective. You can always ask on the yosys GH or slack for confirmation.