Global Routing#

The global routing module in OpenROAD (grt) is based on FastRoute, an open-source global router originally derived from Iowa State University’s FastRoute4.1 algorithm.

Commands#

Note

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

Global Route#

This command performs global routing with the option to use a guide_file. You may also choose to use incremental global routing using -start_incremental.

global_route 
    [-guide_file out_file]
    [-congestion_iterations iterations]
    [-congestion_report_file file_name]
    [-congestion_report_iter_step steps]
    [-grid_origin {x y}]
    [-critical_nets_percentage percent]
    [-skip_large_fanout_nets fanout]
    [-allow_congestion]
    [-snapshot_batched_width width]
    [-verbose]
    [-start_incremental]
    [-end_incremental]
    [-use_cugr]
    [-resistance_aware]
    [-infinite_cap]

Options#

Switch Name	Description
`-guide_file`	Set the output guides file name (e.g., `route.guide`).
`-congestion_iterations`	Set the number of iterations made to remove the congestion of the routing. The default value is `50` for FastRoute and `5` when `-use_cugr` is set; the allowed values are integers `[0, MAX_INT]`.
`-congestion_report_file`	Set the file name to save the congestion report. The file generated can be read by the DRC viewer in the GUI (e.g., `report_file.rpt`).
`-congestion_report_iter_step`	Set the number of iterations to report. The default value is `0`, and the allowed values are integers `[0, MAX_INT]`.
`-grid_origin`	Set the (x, y) origin of the routing grid in DBU. For example, `-grid_origin {1 1}` corresponds to the die (0, 0) + 1 DBU in each x–, y- direction.
`-critical_nets_percentage`	Set the percentage of nets with the worst slack value that are considered timing critical, having preference over other nets during congestion iterations (e.g. `-critical_nets_percentage 30`). The default value is `0`, and the allowed values are integers `[0, MAX_INT]`.
`-skip_large_fanout_nets`	Skips routing for nets with a fanout higher than the specified limit. Nets above this pin count threshold are ignored by the global router and will not have routing guides, meaning they will also be skipped during detailed routing. This option is useful in debugging or estimation flows where high-fanout nets (such as pre-CTS clock nets) can be ignored. The default value is 0, indicating no fanout limit. The default value is `MAX_INT`. The allowed values are integers `[0, MAX_INT]`.
`-allow_congestion`	Allow global routing results to be generated with remaining congestion. The default is false.
`-verbose`	This flag enables the full reporting of the global routing.
`-start_incremental`	This flag initializes the GRT listener to get the net modified. The default is false.
`-end_incremental`	This flag run incremental GRT with the nets modified. The default is false.
`-use_cugr`	This flag run GRT using CUGR as the router solver. NOTE: this is not ready for production.
`-resistance_aware`	This flag enables resistance-aware layer assignment and 3D routing. NOTE: this is not ready for production.
`-infinite_cap`	Enables “infinite” gcell capacity for testing purpose. NOTE: this is not recommended for production flows.
`-snapshot_batched_width`	Set the semantic width of snapshot-batched routing (max batches per wave). The default is `0`, preserving the non-batched behavior. Set a positive integer to enable batched routing; allowed values are integers `[1, MAX_INT]`. Execution width still follows `set_thread_count`. NOTE: this is not recommended for production flows; it is intended for exploration and research projects.

Set Routing Layers#

This command sets the minimum and maximum routing layers for signal and clock nets. Example: set_routing_layers -signal Metal2-Metal10 -clock Metal6-Metal9

set_routing_layers
    [-signal min-max]
    [-clock min-max]

Options#

Switch Name	Description
`-signal`	Set the min and max routing signal layer (names) in this format “%s-%s”.
`-clock`	Set the min and max routing clock layer (names) in this format “%s-%s”.

Set Macro Extension#

This command sets the halo (in terms of GCells) along the boundaries of macros. A GCell is typically defined in terms of Mx routing tracks. Example: set_macro_extension 2

set_macro_extension extension

Options#

Argument Name	Description
`extension`	Number of `GCells` added to the blockage boundaries from macros. The default `GCell` size is 15 `M3` pitches.

Set Global Routing Layer Adjustment#

The set_global_routing_layer_adjustment command sets routing resource adjustments in the routing layers of the design. Such adjustments reduce the number of routing tracks that the global router assumes to exist. This promotes the spreading of routing and reduces peak congestion, to reduce challenges for detailed routing.

You can set adjustment for a specific layer, e.g., set_global_routing_layer_adjustment Metal4 0.5 reduces the routing resources of routing layer Metal4 by 50%. You can also set adjustment for all layers at once using *, e.g., set_global_routing_layer_adjustment * 0.3 reduces the routing resources of all routing layers by 30%. And, you can also set resource adjustment for a layer range, e.g.: set_global_routing_layer_adjustment Metal4-Metal8 0.3 reduces the routing resources of routing layers Metal4, Metal5, Metal6, Metal7 and Metal8 by 30%.

Negative adjustment values can be used to increase the capacity of a given metal layer. For example, set_global_routing_layer_adjustment Metal5 -0.5 will increase the total capacity of Metal5 by 50%.

set_global_routing_layer_adjustment layer adjustment

Options#

Argument Name	Description
`layer`	String for the layer name.
`adjustment`	Float indicating the percentage reduction of each edge in the specified layer.

Set Global Routing Region Adjustment#

Set global routing region adjustment. Example: set_global_routing_region_adjustment {1.5 2 20 30.5} -layer Metal4 -adjustment 0.7

set_global_routing_region_adjustment
    {lower_left_x lower_left_y upper_right_x upper_right_y}
    -layer layer 
    -adjustment adjustment

Options#

Switch Name	Description
`lower_left_x`, `lower_left_y`, `upper_right_x` , `upper_right_y`	Bounding box to consider.
`-layer`	String for the layer name.
`-adjustment`	Float indicating the percentage reduction of each edge in the specified layer.

Set Global Routing Randomness#

The command randomizes global routing by shuffling the order of the nets and randomly subtracts or adds to the capacities of a random set of edges.

Example: set_global_routing_random -seed 42 \ -capacities_perturbation_percentage 50 \ -perturbation_amount 2

set_global_routing_random 
    [-seed seed]
    [-capacities_perturbation_percentage percent]
    [-perturbation_amount value]

Options#

Switch Name	Description
`-seed`	Sets the random seed (must be non-zero for randomization).
`-capacities_perturbation_percentage`	Sets the percentage of edges whose capacities are perturbed. By default, the edge capacities are perturbed by adding or subtracting 1 (track) from the original capacity.
`-perturbation_amount`	Sets the perturbation value of the edge capacities. This option is only meaningful when `-capacities_perturbation_percentage` is used.

Set Specific Nets to Route#

The set_nets_to_route command defines a list of nets to route. Only the nets defined in this command are routed, leaving the remaining nets without any global route guides.

set_nets_to_route 
    net_names 

Options#

Switch Name	Description
`net_names`	Tcl list of set of nets (e.g. `{net1, net2}`).

Repair Antennas#

The repair_antennas command checks the global routing for antenna violations and repairs the violations by inserting diodes near the gates of the violating nets. By default the command runs only one iteration to repair antennas. Filler instances added by the filler_placement command should NOT be in the database when repair_antennas is called.

See LEF/DEF 5.8 Language Reference, Appendix C, “Calculating and Fixing Process Antenna Violations” for a description of antenna violations.

If no diode_cell argument is specified the LEF cell with class CORE, ANTENNACELL will be used. If any repairs are made the filler instances are remove and must be placed with the filler_placement command.

If the LEF technology layer ANTENNADIFFSIDEAREARATIO properties are constant instead of PWL, inserting diodes will not improve the antenna ratios, and thus, no diodes are inserted. The following warning message will be reported:

[WARNING GRT-0243] Unable to repair antennas on net with diodes.

repair_antennas 
    [diode_cell]
    [-iterations iterations]
    [-ratio_margin margin]

Options#

Switch Name	Description
`diode_cell`	Diode cell to fix antenna violations.
`-iterations`	Number of iterations. The default value is `1`, and the allowed values are integers `[0, MAX_INT]`.
`-ratio_margin`	Add a margin to the antenna ratios. The default value is `0`, and the allowed values are integers `[0, 100]`.

Draw Route Segments#

The draw_route_segments command draws the route segments for a set of nets in the GUI.

draw_route_segments
    net_names
    [-show_pin_locations]

Options#

Switch Name	Description
`net_names`	Tcl list of nets (e.g. `{net1 net2}`).
`-show_pin_locations`	Draw circles for the pin positions on the routing grid.

Report Wirelength#

The report_wire_length command reports the wire length of the nets. Use the -global_route and the -detailed_route flags to report the wire length from global and detailed routing, respectively. If none of these flags are used, the tool will identify the state of the design and report the wire length accordingly.

Example: report_wire_length -net {clk net60} -global_route -detailed_route -verbose -file out.csv

report_wire_length 
    [-net net_list]
    [-file file]
    [-global_route]
    [-detailed_route]
    [-verbose]
    [-summary]

Options#

Switch Name	Description
`-net`	List of nets to report the wirelength. Use `*` to report the wire length for all nets of the design.
`-file`	The name of the file for the wirelength report.
`-global_route`	Report the wire length of the global routing.
`-detailed_route`	Report the wire length of the detailed routing.
`-verbose`	This flag enables the full reporting of the layer-wise wirelength information.
`-summary`	This flag reports the wire length for each layer of the design.

Global Route Debug Mode#

The global_route_debug command allows you to start a debug mode to view the status of the Steiner Trees. It also allows you to dump the input positions for the Steiner tree creation of a net. This must be used before calling the global_route command. Set the name of the net and the trees that you want to visualize.

global_route_debug 
    [-st]
    [-rst]
    [-tree2D]
    [-tree3D]
	[-edges3D]
    [-saveSttInput file_name]
    [-net net_name]

Options#

Switch Name	Description
`-st`	Show the Steiner Tree generated by `stt`.
`-rst`	Show the Rectilinear Steiner Tree generated by `grt`.
`-tree2D`	Show the Rectilinear Steiner Tree generated by `grt` after the congestion iterations.
`-tree3D`	Show the 3D Rectilinear Steiner Tree post-layer assignment.
`-edges3D`	Show each edge being rerouted post-layer assignment.
`-saveSttInput`	File name to save `stt` input of a net.
`-net`	The name of the net name to be displayed.

Read Global Routing Guides#

This command reads global routing guides.

read_guides file_name 

Options#

Switch Name	Description
`file_name`	Path to global routing guide.

Write Global Routing Segments#

This command writes global routing segments, the raw routing data generated by the global routing tool.

write_global_route_segments file_name 

Options#

Switch Name	Description
`file_name`	Path to global routing segments file.

Read Global Routing Segments#

This command reads global routing segments, the raw routing data generated by the global routing tool. Reading this format allows to perform parasitics extraction, repair antennas and incremental routing over the input segments file.

read_global_route_segments file_name 

Options#

Switch Name	Description
`file_name`	Path to global routing segments file.

Estimate Path Resistance Between Two Pins#

This command calculates the path resistance between two pins considering the vias and wires connecting them. The two pins need to be connected by the same wire.

estimate_path_resistance pin_name_1 pin_name_2 [-verbose]

Options#

Switch Name	Description
`pin_name_1`	Pin name 1 (e.g., `_437_/Y`).
`pin_name_2`	Pin name 1 (e.g., `_438_/A`).
`-verbose`	Print path details.

Example scripts#

Examples scripts demonstrating how to run FastRoute on a sample design of gcd as follows:

./test/gcd.tcl

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
`check_routing_layer`	Check if the layer is within the min/max routing layer specified.
`parse_layer_name`	Get routing layer number from layer name
`parse_layer_range`	Parses a range from `layer_range` argument of format (%s-%s). `cmd` argument is not used.
`check_region`	Checks the defined region if its within the die area.
`have_detailed_route`	Checks if block has detailed route already.

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#

Using the Python interface to grt#

Warning

The Python interface is currently in development and is subject to change.

The Python API tries to stay close to the API defined in the C++ class GlobalRouter that is located here

When initializing a design, a sequence of Python commands might look like the following:

from openroad import Design, Tech
tech = Tech()
tech.readLef(...)
design = Design(tech)
design.readDef(...)
gr = design.getGlobalRouter()

Here are some options to the global_route command. (See GlobalRouter.h for a complete list)

gr.setGridOrigin(x, y)                     # int, default 0,0
gr.setCongestionReportFile(file_name)      # string
gr.setCongestionIterations(n)                # int, default 50
gr.setAllowCongestion(allowCongestion)     # boolean, default False
gr.setCriticalNetsPercentage(percentage)   # float
gr.setMinRoutingLayer(minLayer)            # int
gr.setMaxRoutingLayer(maxLayer)            # int
gr.setMinLayerForClock(minLayer)           # int
gr.setMaxLayerForClock(maxLayer)           # int
gr.setVerbose(v)                           # boolean, default False

and when ready to actually do the global route:

gr.globalRoute(save_guides)                # boolean, default False

If you have set save_guides to True, you can then save the guides in file_name with:

design.getBlock().writeGuides(file_name)

You can find the index of a named layer with

lindex = tech.getDB().getTech().findLayer(layer_name)

or, if you only have the Python design object

lindex = design.getTech().getDB().getTech().findLayer(layer_name)

Be aware that much of the error checking is done in Tcl, so that with the current C++ / Python API, that might be an issue to deal with. There are also some useful Python functions located in the grt_aux.py file but these are not considered a part of the final API and may be subject to change.

FAQs#

Check out GitHub discussion about this tool.

References#

Database comes from OpenDB
FastRoute 4.1 documentation. The FastRoute4.1 version was received from Yue Xu on June 15, 2019.
Min Pan, Yue Xu, Yanheng Zhang and Chris Chu. “FastRoute: An Efficient and High-Quality Global Router. VLSI Design, Article ID 608362, 2012.” Available here.
C. J. Alpert, T. C. Hu, J. H. Huang, A. B. Kahng and D. Karger, “Prim-Dijkstra Tradeoffs for Improved Performance-Driven Global Routing”, IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems 14(7) (1995), pp. 890-896. Available here.

License#

BSD 3-Clause License. See LICENSE file.

Global Routing

Contents

Global Routing#

Commands#

Global Route#

Options#

Set Routing Layers#

Options#

Set Macro Extension#

Options#

Set Global Routing Layer Adjustment#

Options#

Set Global Routing Region Adjustment#

Options#

Set Global Routing Randomness#

Options#

Set Specific Nets to Route#

Options#

Repair Antennas#

Options#

Draw Route Segments#

Options#

Report Wirelength#

Options#

Global Route Debug Mode#

Options#

Read Global Routing Guides#

Options#

Write Global Routing Segments#

Options#

Read Global Routing Segments#

Options#

Estimate Path Resistance Between Two Pins#

Options#

Example scripts#

Useful Developer Commands#

Regression tests#

Limitations#

Using the Python interface to grt#

FAQs#

References#

License#