LU Factorization of the G Matrix failed during analyze_power_grid

[maliberty]

Discussed in #2791

^{Originally posted by rixmaestro February 6, 2025}
Hello! I would like to know how to debug this error:

"[ERROR PSM-0010] LU factorization of the G Matrix failed. SparseLU solver message: THE MATRIX IS STRUCTURALLY SINGULAR ... ZERO COLUMN AT"

I have tried with the gf180/aes design and with my own design in another PDK and it always give this error.

Note that I have properly set the voltage using set_pdnsim_net_voltage command. There is also an info message saying:

[INFO PSM-0040] All shapes on net VDD are connected.

Just for an example, for my own design, the pdn.tcl contains the following:

add_global_connection -defer_connection -net {VDD} -inst_pattern {.*} -pin_pattern {^VDD$} -power
add_global_connection -defer_connection -net {VSS} -inst_pattern {.*} -pin_pattern {^VSS$} -ground
global_connect

set_voltage_domain -name {CORE} -power {VDD} -ground {VSS}

define_pdn_grid -name {block} -voltage_domains {CORE}
add_pdn_stripe -grid {block} -layer {METAL1} -followpins -width 0.47
add_pdn_stripe -grid {block} -layer {METAL4} -width 4 -pitch 60.12 -spacing 8.65 -offset 35.74 -extend_to_boundary -number_of_straps 6
add_pdn_stripe -grid {block} -layer {METAL5} -width 4 -pitch 470.4 -offset 56.84 -extend_to_boundary
add_pdn_connect -grid {block} -layers {METAL1 METAL4}
add_pdn_connect -grid {block} -layers {METAL4 METAL5}

If more information is needed, just inform me. Thank you!

[maliberty]

From the discussion

An example self-contained test case is here:
https://drive.google.com/file/d/1n1bztnZpidUOQDdJ2g2QQUC14obeRn_K/view?usp=drive_link

After running the scripts, I start openroad and read the lef files, lib files, and the output def file. Then, I do set_pdnsim_net_voltage command and analyze_power_grid command.

[maliberty]

gf180/aes isn't running power drop, see 6_report.log:

IR drop analysis for power nets is skipped because PWR_NETS_VOLTAGES is undefined
IR drop analysis for ground nets is skipped because GND_NETS_VOLTAGES is undefined

The test case provided is for global placement and doesn't run IR-drop analysis either.