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Detailed Placement

The detailed placement module in OpenROAD (dpl) is based on OpenDP, or Open-Source Detailed Placement Engine. Its key features are:

  • Fence region.
  • Fragmented ROWs.

Commands 

- Parameters in square brackets `[-param param]` are optional.
- Parameters without square brackets `-param2 param2` are required.

Detailed Placement

The detailed_placement command performs detailed placement of instances to legal locations after global placement.

detailed_placement
    [-max_displacement disp|{disp_x disp_y}]
    [-disallow_one_site_gaps]
    [-report_file_name filename]

Options

Switch Name Description
-max_displacement Max distance that an instance can be moved (in microns) when finding a site where it can be placed. Either set one value for both directions or set {disp_x disp_y} for individual directions. The default values are {0, 0}, and the allowed values within are integers [0, MAX_INT].
-disallow_one_site_gaps Disable one site gap during placement check.
-report_file_name File name for saving the report to (e.g. report.json.)

Set Placement Padding

The set_placement_padding command sets left and right padding in multiples of the row site width. Use the set_placement_padding command before legalizing placement to leave room for routing. Use the -global flag for padding that applies to all instances. Use -instances for instance-specific padding. The instances insts can be a list of instance names, or an instance object returned by the SDC get_cells command. To specify padding for all instances of a common master, use the -filter "ref_name == " option to get_cells.

set_placement_padding   
    -global|-masters masters|-instances insts
    [-right site_count]
    [-left site_count]

Options 

Either one of these flags must be set: `-global | -masters | -instances`.
The order of preference is `global > masters > instances`
Switch Name Description
-global Set padding globally using left and right values.
-masters Set padding only for these masters using left and right values.
-instances For -instances, you will set padding only for these insts using left and right values.
-left Left padding (in site count).
-right Right padding (in site count).
instances Set padding for these list of instances. Not to be confused with the -instances switch above.

Filler Placement

The filler_placement command fills gaps between detail-placed instances to connect the power and ground rails in the rows. filler_masters is a list of master/macro names to use for filling the gaps. Wildcard matching is supported, so FILL* will match, e.g., FILLCELL_X1 FILLCELL_X16 FILLCELL_X2 FILLCELL_X32 FILLCELL_X4 FILLCELL_X8. To specify a different naming prefix from FILLER_ use -prefix <new prefix>.

filler_placement
    [-prefix prefix]
    filler_masters

Options

Switch Name Description
-prefix Prefix to name the filler cells. The default value is FILLER_.
filler_masters Filler master cells.

Remove Fillers

This command removes all filler cells.

remove_fillers

Check Placement

The check_placement command checks the placement legality. It returns 0 if the placement is legal.

check_placement
    [-verbose]
    [-disallow_one_site_gaps]
    [-report_file_name filename]

Options

Switch Name Description
-verbose Enable verbose logging.
-disallow_one_site_gaps Disable one site gap during placement check.
-report_file_name File name for saving the report to (e.g. report.json.

Optimize Mirroring

The optimize_mirroring command mirrors instances about the Y axis in a weak attempt to reduce the total half-perimeter wirelength (HPWL).

optimize_mirroring

Useful Developer Commands

If you are a developer, you might find these useful. More details can be found in the source file or the swig file.

Command Name Description
detailed_placement_debug Debug detailed placement.
get_masters_arg Get masters from a design.
get_inst_bbox Get bounding box of an instance.
get_inst_grid_bbox Get grid bounding box of an instance.
format_grid Format grid (takes in length x and site width w as inputs).
get_row_site Get row site name.

Example scripts

Examples scripts demonstrating how to run dpl on a sample design of aes as follows:

./test/aes.tcl

Regression tests

There are a set of regression tests in ./test. Refer to this section for more information.

Simply run the following script: 

./test/regression

Limitations

FAQs

Check out GitHub discussion about this tool.

Authors

  • SangGi Do and Mingyu Woo (respective Ph. D. advisors: Seokhyeong Kang, Andrew B. Kahng).
  • Rewrite and port to OpenDB/OpenROAD by James Cherry, Parallax Software

References

  1. Do, S., Woo, M., & Kang, S. (2019, May). Fence-region-aware mixed-height standard cell legalization. In Proceedings of the 2019 on Great Lakes Symposium on VLSI (pp. 259-262). (.pdf)

License

BSD 3-Clause License. See LICENSE file.