Add library of useful functions for doing manual placement of cells

[mithro]

Description

It would be nice if the OpenROAD tool provides a set of functions to the TCL & Python scripting interface which made it quick and easy to do manual placement of a certain sets of cells.

Some ideas include;

• place_column -- Place the selected cells into a vertical column. Options could include;
  • packed for placing them as close together as possible.
  • equal for placing them equally distributed between top and bottom coordinates.
  • global for placing them in the rough locations which need to be legalized into actual valid positions.
  • legalize (or maybe detailed) for placing them directly into legalized positions.
• place_row -- Place the selected cells into a horizontal row
  • Same as place_column.
• place_array -- Place the selected cells into a grid / array pattern.
  • Same as place_column.

Some related functions could include;

• legalize_cells -- Legalize the set of cells into correct placements.
• route_net -- Route the selected set of nets.

This are likely to be very useful in things like;

• Automated analog like OpenFASoC
• Building blocks like DFFRAM does
• Distributing cells for wave style computation
• Placing input / output flops in certain locations
• Other things I haven't thought of

Suggested Solution

No response

Additional Context

No response

[Dolu1990]

Hi,

I think I hit the same issue. I have congestions problems on a register-file using sky130 (doesn't pass at 20% density), and wanted to try helping the place and route by providing "fixed location" in column for the register-file latches.

[mithro]

@Dolu1990 - You might find using DFFRAM as an alternative solution.

[maliberty]

Note that DFFRAM is rather skywater specific and some layouts are far from optimal.

[Dolu1990]

@mithro Thanks ^^ It seems like DFFRAM won't work for my usecase (i would need 4R 2W and more)

[mithro]

@Dolu1990 - You should know how to build a 4R 2W out of DFFRAM blocks, same thing we do as in FPGAs -- https://tomverbeure.github.io/2019/08/03/Multiport-Memories.html :-)

[mithro]

@Dolu1990 - You should also log a feature request on the DFFRAM repository. BTW If you are doing this as part of funded research, funding AUC is extremely cheap.

[Dolu1990]

@mithro

You should know how to build a 4R 2W out of DFFRAM blocks, same thing we do as in FPGAs

Yes right ^^

You should also log a feature request on the DFFRAM repository

Done : https://github.com/AUCOHL/DFFRAM/issues/192

If you are doing this as part of funded research, funding AUC is extremely cheap.

It is part of a small exploratory project (~100h work) to see where are the bottleneck in porting NaxRiscv to asic, not enough left for it, but thanks for the tips, i keep it in mind :)

[maliberty]

Fwiw I did start a rewrite of DFFRAM in OR as a spare time project. If someone has interest in picking it up I would be glad to share the in progress code.

[rovinski]

@maliberty that might be a good student project? If you share the code I can determine further.

[maliberty]

fwiw I put the code at https://github.com/The-OpenROAD-Project/OpenROAD/pull/4496 - this is not complete and is not proposed a solution to anything in its current form. If someone wants to pick it up and complete it that would be great.

[QuantamHD]

We should take a page from CSS Grid https://css-tricks.com/snippets/css/complete-guide-grid/ if we're looking for more generic layout primitives.