How do you build a power state table using create_pst and add_pst_state?

Short Answer

First give each supply port its named states with add_port_state (UPF), then declare the table and its column order with create_pst (UPF), then add one row per legal mode with add_pst_state (UPF). Any combination you do not list is illegal. All three commands are legacy in IEEE 1801-2015, which recommends add_power_state (UPF) instead, but ICC2 and PrimeTime still read them.

Technical Explanation

• Port states: add_port_state VDDdsp -state {DSP_HV 1.1} -state {DSP_LV 0.9} (UPF) names each voltage a supply can take, or off.
• Table: create_pst MYCHIP_pst -supplies {...} (UPF) fixes the column order once.
• Rows: add_pst_state PM3 -pst MYCHIP_pst -state {...} (UPF) lists one state per supply, in the same column order.
• Why it matters: the table decides which crossings can see an off or lower-voltage driver, so it drives isolation and level-shifter checks.
• Isolation insertion follows the set_isolation strategies, not the table; ICC2 reports mismatches with check_mv_design (ICC2).
• A missing legal row makes a real mode look illegal; an extra row demands cells you do not need.

# [UPF]  mychip.upf
add_port_state VDD1p0 -state {HV 1.0}
add_port_state VDD0p9 -state {LV 0.9}
add_port_state VDDdsp -state {DSP_HV 1.1} -state {DSP_LV 0.9}
add_port_state PD_COP_SW/VDD -state {COP_ON 1.0} -state {COP_OFF off}
create_pst MYCHIP_pst -supplies {VDD1p0 VDD0p9 VDDdsp PD_COP_SW/VDD}
add_pst_state PM1 -pst MYCHIP_pst -state {HV LV DSP_HV COP_ON}
add_pst_state PM2 -pst MYCHIP_pst -state {HV LV DSP_LV COP_ON}
add_pst_state PM3 -pst MYCHIP_pst -state {HV LV DSP_HV COP_OFF}
add_pst_state PM4 -pst MYCHIP_pst -state {HV LV DSP_LV COP_OFF}
# [ICC2]  icc2_shell
report_pst

What To Check

• Every supply in -supplies has port states defined first.
• Each row lists exactly one state per column, in column order.
• Every mode the chip can enter, including wake-up transitions, has a row.
• No row keeps PD_COP on while an always-on supply it needs is off.

Healthy, Suspicious & Hard-stop Results

• Healthy (illustrative): report_pst shows four rows, PM1 to PM4, with COP_OFF only in PM3 and PM4.
• Suspicious (illustrative): report_pst -derived shows a combination you never listed; find its source before trusting isolation coverage.
• Hard stop: A row with the wrong number of entries fails to load, or a mode the firmware uses is missing.

What The Interviewer Is Testing

• Can you build a PST in the right order: port states, table, rows?
• Do you know the PST commands are legacy and what replaces them?

Follow-up Question & Model Response

"How would you write the same intent with add_power_state?"

Candidate Model Response: You give each supply set its states, for example SS_COP with COP_ON and COP_OFF through -supply_expr. You then create a power state group and add system states such as PM3 with a -logic_expr over the supply set states. The result is the same set of legal modes, but tied to supply sets instead of ports. That is the form IEEE 1801-2015 recommends, covered in the add_power_state question.