Detailed Routing

The Detailed Routing (drt) module in OpenROAD is based on the open-source detailed router, TritonRoute. TritonRoute consists of several main building blocks, including pin access analysis, track assignment, initial detailed routing, search and repair, and a DRC engine. The initial development of the router is inspired by the ISPD-2018 initial detailed routing contest. However, the current framework differs and is built from scratch, aiming for an industrial-oriented scalable and flexible flow.

TritonRoute provides industry-standard LEF/DEF interface with support of ISPD-2018 and ISPD-2019 contest-compatible route guide format.

Commands

Note

• Parameters in square brackets [-param param] are optional.

• Parameters without square brackets -param2 param2 are required.

Detailed Route

This command performs detailed routing.

Developer arguments

• -or_seed, -or_k

Distributed arguments

• -distributed , -remote_host, -remote_port, -shared_volume, -cloud_size

Pin Access arguments

• -via_in_pin_bottom_layer, -via_in_pin_top_layer, -via_access_layer, -min_access_points

detailed_route 
    [-output_maze filename]
    [-output_drc filename]
    [-output_guide_coverage filename]
    [-drc_report_iter_step step]
    [-db_process_node name]
    [-disable_via_gen]
    [-droute_end_iter iter]
    [-via_in_pin_bottom_layer layer]
    [-via_in_pin_top_layer layer]
    [-via_access_layer layer]
    [-or_seed seed]
    [-or_k k]
    [-bottom_routing_layer layer]
    [-top_routing_layer layer]
    [-verbose level]
    [-distributed]
    [-remote_host rhost]
    [-remote_port rport]
    [-shared_volume vol]
    [-cloud_size sz]
    [-clean_patches]
    [-no_pin_access]
    [-min_access_points count]
    [-save_guide_updates]
    [-repair_pdn_vias layer]
    [-single_step_dr]

Options

Switch Name	Description
-output_maze	Path to output maze log file (e.g. output_maze.log).
-output_drc	Path to output DRC report file (e.g. output_drc.rpt).
-output_guide_coverage	Path to output guide coverage file (e.g. sample_coverage.csv).
-drc_report_iter_step	Report DRC on each iteration which is a multiple of this step. The default value is 0, and the allowed values are integers [0, MAX_INT].
-db_process_node	Specify the process node.
-disable_via_gen	Option to diable via generation with bottom and top routing layer. The default value is disabled.
-droute_end_iter	Number of detailed routing iterations. The default value is -1, and the allowed values are integers [1, 64].
-via_in_pin_bottom_layer	Refer to pin access arguments here.
-via_in_pin_top_layer	Refer to pin access arguments here.
-via_access_layer	Refer to pin access arguments here.
-min_access_points	Refer to pin access arguments here.
-or_seed	Refer to developer arguments here.
-or_k	Refer to developer arguments here.
-bottom_routing_layer	Deprecated. Use the set_routing_layers command instead.
-top_routing_layer	Deprecated. Use the set_routing_layers command instead.
-verbose	Sets verbose mode if the value is greater than 1, else non-verbose mode (must be integer, or error will be triggered.)
-distributed	Refer to distributed arguments here.
-remote_host	Refer to distributed arguments here.
-remote_port	Refer to distributed arguments here.
-shared_volume	Refer to distributed arguments here.
-cloud_size	Refer to distributed arguments here.
-clean_patches	Clean unneeded patches during detailed routing.
-no_pin_access	Disables pin access for routing.
-save_guide_updates	Flag to save guides updates.
-repair_pdn_vias	This option is used for PDKs where M1 and M2 power rails run in parallel.

Developer arguments

Some arguments that are helpful for developers are listed here.

Switch Name	Description
-or_seed	Random seed for the order of nets to reroute. The default value is -1, and the allowed values are integers [0, MAX_INT].
-or_k	Number of swaps is given by \(k * sizeof(rerouteNets)\). The default value is 0, and the allowed values are integers [0, MAX_INT].

Detailed Route Debugging

The following command and arguments are useful when debugging error messages from drt and to understand its behavior.

detailed_route_debug 
    [-pa]
    [-ta]
    [-dr]
    [-maze]
    [-net name]
    [-pin name]
    [-box x1 y1 x2 y2]
    [-iter iter]
    [-pa_markers]
    [-dump_dr]
    [-dump_dir dir]
    [-snapshot_dir dir]
    [-dump_last_worker]
    [-pa_edge]
    [-pa_commit]
    [-write_net_tracks]

Options

Switch Name	Description
-pa	Enable debug for pin access.
-ta	Enable debug for track assignment.
-dr	Enable debug for detailed routing.
-maze	Enable debug for maze routing.
-net	Enable debug for net name.
-pin	Enable debug for pin name.
-box	Set the box for debugging given by lower left/upper right coordinates.
-worker	Debugs routes that pass through the point {x, y}.
-iter	Specifies the number of debug iterations. The default value is 0, and the accepted values are integers [0, MAX_INT.
-pa_markers	Enable pin access markers.
-dump_dr	Filename for detailed routing dump.
-dump_dir	Directory for detailed routing dump.
-snapshot_dir	Directory for snapshots produced if the debug level of DRT snapshot is set to 1.
-pa_edge	Enable visibility of pin access edges.
-pa_commit	Enable visibility of pin access commits.
-write_net_tracks	Enable writing of net track assigments.

Check Pin Access

This function checks pin access.

pin_access
    [-db_process_node name]
    [-bottom_routing_layer layer]
    [-top_routing_layer layer]
    [-via_access_layer layer]
    [-via_in_pin_bottom_layer layer]
    [-via_in_pin_top_layer layer]
    [-min_access_points count]
    [-verbose level]
    [-distributed]
    [-remote_host rhost]
    [-remote_port rport]
    [-shared_volume vol]
    [-cloud_size sz]

Options

Switch Name	Description
-db_process_node	Specify process node.
-bottom_routing_layer	Deprecated. Use the set_routing_layers command instead.
-top_routing_layer	Deprecated. Use the set_routing_layers command instead.
-via_access_layer	Refer to pin access arguments here.
-via_in_pin_bottom_layer	Refer to pin access arguments here.
-via_in_pin_top_layer	Refer to pin access arguments here.
-min_access_points	Refer to pin access arguments here.
-verbose	Sets verbose mode if the value is greater than 1, else non-verbose mode (must be integer, or error will be triggered.)
-distributed	Refer to distributed arguments here.
-remote_host	Refer to distributed arguments here.
-remote_port	Refer to distributed arguments here.
-shared_volume	Refer to distributed arguments here.
-cloud_size	Refer to distributed arguments here.

Pin Access Arguments

We have compiled all pin access related arguments in this section.

Switch Name	Description
-via_access_layer	Top via access layer name. Any pin on this layer or below can only be accessed through a via, disallowing planar access.
-via_in_pin_bottom_layer	Via-in pin bottom layer name. Used in conjunction with via_in_pin_top_layer to specify the layer range for via-in-pin rules.
-via_in_pin_top_layer	Via-in pin top layer name. Used in conjunction with via_in_pin_bottom_layer to specify the layer range for via-in-pin rules. For pins within this layer range, any via enclosure must be fully contained within the pin boundary and cannot extend beyond the pin edges.
-min_access_points	Minimum number of access points per pin.

Distributed Arguments

We have compiled all distributed arguments in this section.

Note

Additional setup is required. Please refer to this guide.

Switch Name	Description
-distributed	Enable distributed mode with Kubernetes and Google Cloud.
-remote_host	The host IP.
-remote_port	The value of the port to access from.
-shared_volume	The mount path of the nfs shared folder.
-cloud_size	The number of workers.

Set Routing Watermark Strength

This command sets the cost multiplier the detailed router applies to wiring against a layer’s preferred direction on nets tagged by set_routing_watermark. A larger value suppresses wrong-way wiring more strongly on those nets, which is what carries the routing watermark. Preferred-direction wiring, pin access and untagged nets are unaffected. This is router configuration and does not persist in the database, so call it in the same process as detailed_route, before it.

set_routing_watermark_strength
    strength

Options

Switch Name	Description
strength	Finite cost multiplier from 0 to 10000 inclusive. 1 tags nets without biasing them. Defaults to 100.

Scaled edge costs and the path costs built from them saturate at the router’s maximum cost rather than wrapping. Very large strengths make distinct expensive paths indistinguishable, which is why the range is bounded.

Get Routing Watermark Strength

This command returns the cost multiplier currently in effect.

get_routing_watermark_strength

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_route_set_default_via	Set default via.
detailed_route_set_unidirectional_layer	Set unidirectional layer.
step_dr	Refer to function detailed_route_step_drt.
check_drc	Refer to function check_drc_cmd.

Example scripts

Example script demonstrating how to run TritonRoute on a sample design of gcd in the Nangate45 technology node.

# single machine example 
./test/gcd_nangate45.tcl

# distributed example
./test/gcd_nangate45_distributed.tcl

Regression tests

There are a set of regression tests in ./test. For more information, refer to this section.

Simply run the following script:

./test/regression

Limitations

References

Please cite the following paper(s) for publication:

1. A. B. Kahng, L. Wang and B. Xu, “TritonRoute: The Open Source Detailed Router”, IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems (2020), doi:10.1109/TCAD.2020.3003234. (.pdf)

2. A. B. Kahng, L. Wang and B. Xu, “The Tao of PAO: Anatomy of a Pin Access Oracle for Detailed Routing”, Proc. ACM/IEEE Design Automation Conf., 2020, pp. 1-6. (.pdf)

Authors

TritonRoute was developed by graduate students Lutong Wang and Bangqi Xu from UC San Diego, and serves as the detailed router in the OpenROAD project.

License

BSD 3-Clause License. See LICENSE file.