The-OpenROAD-Project
placement.tcl removes resizer buffers
In run_placement scripts/tcl_commands/placement.tcl run_resizer_design
if { [info exists ::env(DONT_BUFFER_PORTS) ]} {
remove_buffers
}
This undoes any buffers inserted for long wire, max slew, max cap design rule repair done by repair_design in run_resizer_design. The buffers should be removed BEFORE repair to removes buffers inserted by synthesis.
I've often wondered what remove_buffers is trying to achieve. In particular it seems to completely remove buffer tree insertion by abc, and OpenROAD has nothing similar to replace it with. Do we have evidence of abc over buffering designs?
@antonblanchard abc is buffering based on wire load models and may not do a good job because of it. Trying to have the resizer fix their buffer trees hasn't worked well in the past. The best solution would be to have resizer have a stronger buffer tree capability rather than rely on the abc buffering. In any case it seems a bad idea to remove the resizer results.
@maliberty Adding support for better buffering in the resizer would be great and would hopefully fix the issues I see in my designs. Agree that it seems weird to be removing buffers after resizing.
So this was more of a nomenclature problem that has been addressed: This removes buffers placed on specific ports, such as analog ports and the like. This is unavoidable until a public API to set nets and instances as "don't touch" during resizing is surfaces, which the OR team expressed no immediate interest in.
The function has been renamed remove_buffers_from_nets to mitigate any further confusion.
support for dont touch has been going in this week and should be available soon
That's very good to know. Please send the function documentation when it's ready.