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#

Note

  • 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#

Warning

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.