What happens if a retention strategy is given the wrong retention supply, and what UPF mechanism helps prevent this?
From PDVerse Low-Power Physical Design Mentor Guide · pdVerse Mentor Guide
Technical Explanation
If a retention strategy's -retention_power_net/retention_ground_net (or -retention_supply_net) points at a supply that is not genuinely always-on relative to the domain being retained, the retention latches lose power at the same time the domain shuts down and the saved state is corrupted — retention silently fails to do its job. UPF provides a correlation-check mechanism specifically for this: set_retention's -parameters option, with values RET_SUP_COR / NO_RET_SUP_COR (retention-supply correlation) and SAV_RES_COR / NO_SAVE_RES_COR (save/restore correlation), which lets the tool check the correlation between the retention supply and the related save/restore behavior.
Architecture-level Reasoning
Because the retention power net is just another user-specified argument with no built-in guarantee of being always-on, the correlation-check parameters exist precisely to give the tool a way to flag a retention supply that doesn't actually behave the way a retention supply must — rather than relying purely on the author getting the always-on relationship right by inspection.
Step-by-step Walkthrough
1) Declare the retention strategy: set_retention -domain retention_power_net -retention_ground_net . 2) If the specified retention_power_net is not actually always-on relative to the domain's own primary supply, retained state is lost across shutdown even though the UPF is syntactically valid. 3) Apply parameters {RET_SUP_COR} (or the corresponding SAV_RES_COR for save/restore correlation) to enable the tool's correlation check between the retention supply and the strategy's expected save/ restore behavior, versus -parameters {NO_RET_SUP_COR}/ {NO_SAVE_RES_COR} to disable it.
Command
set_retention UP_RET_POLICY -domain PD_UP -retention_power_net VDDG
-retention_ground_net VSS -parameters {RET_SUP_COR}Switch-by-switch
-retention_power_net / -retention_ground_net: the supply the
retention elements are backed by — must genuinely be always-on
relative to the domain for retention to function. -parameters
{RET_SUP_COR|NO_RET_SUP_COR}: enables/disables correlation
checking between the retention supply and the strategy. parameters {SAV_RES_COR|NO_SAVE_RES_COR}: enables/disables
correlation checking of the save/restore behavior.Expected Result
A retention strategy whose declared retention supply is confirmed (via the correlation-check parameters) to be consistent with the always-on relationship the strategy depends on, so retained state actually survives domain shutdown.
Possible Implementation Error
Pointing -retention_power_net at the domain's own switched primary supply instead of a genuinely always-on rail, so the retention latch loses power at exactly the moment the domain shuts down and the saved values are lost.
Likely Tool / Clp Warning
This topic is not covered in enough depth here to give a fully reliable answer regarding a specific tool error code for a wrong retention supply beyond the -parameters correlation-check mechanism itself.
Root Cause
set_retention accepts -retention_power_net as a plain userspecified net argument with no automatic verification that it is always-on relative to the retained domain; the correlation-check parameters are the mechanism provided to add that verification.
Debugging Sequence
1) Identify the retention strategy's declared retention_power_net/ground_net (or retention_supply_net). 2) Confirm that net is genuinely always-on across every PST state in which the domain is shut down. 3) Enable -parameters {RET_SUP_COR} (and SAV_RES_COR as applicable) to have the tool check this correlation rather than relying on manual inspection. A retention supply that is not actually always-on is a functional data-loss defect that must be resolved before signoff — retained registers would not actually retain.
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