How do you build a power state table using create_pst and add_pst_state?
From PDVerse Low-Power Physical Design Mentor Guide · pdVerse Mentor Guide
Explanation
A power state table enumerates every legal combination of voltage/ off states across a set of supplies, giving each combination a named mode that other tools and checks can validate the design's actual power behavior against.
Implementation Walkthrough
First declare the table and its ordered list of supplies: create_pst -supplies {port list}. Then add one add_pst_state -pst -state {values} call per legal combination, listing one value per supply in the same order given to -supplies. Mychip's final table is create_pst MYCHIP_pst -supplies {VDD1p0 VDD0p9 VDDdsp PD_COP_SW/VDD}, followed by four add_pst_state calls for modes PM1 through PM4, matching the four power modes and per-domain rules described earlier in the design.
Command
create_pst MYCHIP_pst -supplies {VDD1p0 VDD0p9 VDDdsp PD_COP_SW/VDD}
VDD1p0 (always-on)
PD_COP_SW
VDD1p0_SW (virtual)
becomesthePRIMARY
supplyofPD_COPSwitch-by-switch
-supplies {list} (on create_pst): the ordered list of supply nets/
ports whose states are being tabulated; -pst
(on add_pst_state): which table this state belongs to; -state {values} (on
add_pst_state): the ordered voltage/off values, in the same order as supplies, that define this named power mode -- e.g. PST1 = {VDDG 0.8,
VDD_ON 1.0, VDD_SW 1.0} or PST3 = {0.8, 1.0, off}, showing the switched
supply fully off in that mode.Expected Tool Behavior
The tool can now validate that every operating mode the design actually enters corresponds to one of the declared PST rows, and cross-check isolation/retention/switch strategies against these legal combinations.
Example
The four power-mode rows: PST1={VDDG 0.8, VDD_ON 1.0, VDD_SW 1.0}; PST2={0.8, 1.2, 1.2}; PST3={0.8, 1.0, off}; PST4={0.8, 1.2, off}.
Common Mistake
Omitting a legal combination the design can actually reach (for example an intermediate mode during a power-up sequence), which causes the tool to treat a real transient state as unmodeled or illegal.
Likely Error Or Warning
report_pst -reconcile flags inconsistencies between the declared PST and the states the tool actually derives from the design's power connections.
Debugging Approach
Run report_pst -verbose -reconcile / -derived to see how the declared PST reconciles with what the tool derives, and use query_pst / query_pst_state to inspect a specific table or state programmatically.
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