Rectilinear Steiner Tree

Rectilinear Steiner Tree#

The steiner tree (stt) module in OpenROAD constructs steiner trees used in the global routing (grt) module. Documentation is current under construction.

Commands#

Note

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

  • Parameters without square brackets -param2 param2 are required.

Set Routing Alpha#

This command sets routing alphas for a given net net_name.

By default the global router uses heuristic rectilinear Steiner minimum trees (RSMTs) as an initial basis to construct route guides. An RSMT tries to minimize the total wirelength needed to connect a given set of pins. The Prim-Dijkstra heuristic is an alternative net topology algorithm that supports a trade-off between total wirelength and maximum path depth from the net driver to its loads. The set_routing_alpha command enables the Prim/Dijkstra algorithm and sets the alpha parameter used to trade-off wirelength and path depth. Alpha is between 0.0 and 1.0. When alpha is 0.0 the net topology minimizes total wirelength (i.e. capacitance). When alpha is 1.0 it minimizes longest path between the driver and loads (i.e., maximum resistance). Typical values are 0.4-0.8. You can call it multiple times for different nets.

Example: set_routing_alpha -net clk 0.3 sets the alpha value of 0.3 for net clk.

set_routing_alpha 
    [-net net_name] 
    [-min_fanout fanout]
    [-min_hpwl hpwl]
    [-clock_nets]
    alpha

Options#

Switch Name

Description

-net

Net name.

-min_fanout

Set the minimum number for fanout.

-min_hpwl

Set the minimum half-perimetere wirelength (microns).

-clock_nets

If this flag is set to True, only clock nets will be modified.

alpha

Float between 0 and 1 describing the trade-off between wirelength and path depth.

Example scripts#

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#

License#

BSD 3-Clause License. See LICENSE file.

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