data/markdown/OR_userguide/OR_psm_README.md

IR Drop Analysis

The IR Drop Analysis module in OpenROAD (psm) is based on PDNSim, an open-source static IR analyzer.

Features:

• Report worst IR drop.
• Report worst current density over all nodes and wire segments in the power distribution network, given a placed and PDN-synthesized design.
• Check for floating PDN stripes on the power and ground nets.
• Spice netlist writer for power distribution network wire segments.

(Left): Current Map, (Right): IR drop map

Commands

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

Analyze Power Grid

analyze_power_grid
    [-vsrc vsrc_file]
    [-outfile out_file]
    [-error_file err_file]
    [-enable_em]
    [-em_outfile em_out_file]
    [-net net_name]
    [-dx bump_pitch_x]
    [-dy bump_pitch_y]
    [-node_density val_node_density]
    [-node_density_factor val_node_density_factor]
    [-corner corner]

Options

Switch Name	Description
-vsrc	File to set the location of the power C4 bumps/IO pins. Vsrc_aes.loc file for an example with a description specified here.
-dx,-dy	These arguments set the bump pitch to decide the voltage source location in the absence of a vsrc file. Default bump pitch of 140um used in absence of these arguments and vsrc.
-net	Name of the net to analyze, power or ground net name.
-enable_em	Report current per power grid segment.
-outfile	Write per-instance voltage into the file.
-em_outfile	Write the per-segment current values into a file. This option is only available if used in combination with -enable_em.
-voltage	Sets the voltage on a specific net. If this option is not set, the Liberty file's voltage value is obtained from operating conditions.
-node_density	Node density (in microns) on the standard cell rails. It cannot be used together with -node_density_factor.
-node_density_factor	Factor which is multiplied by standard cell height to determine the node density on the std cell rails. It cannot be used together with -node_density. The default value is 5, and the allowed values are integers [0, MAX_INT].
-corner	Corner to use for analysis.

Check Power Grid

check_power_grid -net net_name

Options

Switch Name	Description
-net	Name of the net to analyze. Must be a power or ground net name.

Write Spice Power Grid

write_pg_spice
    [-vsrc vsrc_file]
    [-outfile out_file]
    [-net net_name]
    [-dx bump_pitch_x]
    [-dy bump_pitch_y]
    [-corner corner]

Options

Switch Name	Description
-vsrc	File to set the location of the power C4 bumps/IO pins. See Vsrc_aes.loc file for an example and its description.
-dx,-dy	Set the bump pitch to decide the voltage source location in the absence of a vsrc file. The default bump pitch is 140um if neither these arguments nor a vsrc file are given.
-net	Name of the net to analyze. Must be a power or ground net name.
-outfile	Write per-instance voltage written into the file.
-corner	Corner to use for analysis.

Set PDNSim Net voltage

set_pdnsim_net_voltage
    [-net net_name]
    [-voltage volt]

Options

Switch Name	Description
-net	Name of the net to analyze. It must be a power or ground net name.
-voltage	Sets the voltage on a specific net. If this option is not given, the Liberty file's voltage value is obtained from operating conditions.

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
find_net	Get a reference to net name.

Example scripts

Example scripts demonstrating how to run PDNSim on a sample design on aes as follows:

./test/aes_test_vdd.tcl
./test/aes_test_vss.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

FAQs

Check out GitHub discussion about this tool.

References

1. PDNSIM documentation
2. Chhabria, V.A. and Sapatnekar, S.S. (no date) The-openroad-project/pdnsim: Power Grid Analysis, GitHub. Available at: https://github.com/The-OpenROAD-Project/PDNSim (Accessed: 24 July 2023). (link)

License

BSD 3-Clause License. See LICENSE file.