Resets do not act alone: power switching and warm resets move state at the same time, and each can undo the guarantees the other relies on. This lesson stays at concept level, because power intent Belongs to its own flow; the RDC engineer needs to know where the two flows collide.
Interaction | What happens | What RDC needs |
|---|---|---|
Isolation during power-down | Isolation cells force boundary signals to safe values while a domain is off, which mimics reset without the reset tree moving. | Neighbour domains must treat isolated inputs like reset-held inputs until the domain is powered and released in order. |
State retention across power cycles | Retained registers keep their values through a power-down that resets their neighbours. | After power-up, retained state and freshly reset state must be consistent; a reset that assumes all-zero neighbours is wrong. |
Warm reset without power cycle | A logic-only reset re-initialises state while power, clocks, and analogue blocks stay up. | The warm sequence must re-establish the same release ordering as a cold reset, even though the power-up sequence that enforced it never runs. |
Cold reset gets its ordering from the power-up sequence: supplies ramp, clocks stabilise, resets release in rank order. A warm reset skips the power-up part, so the ordering has to be enforced by the reset controller alone. The RDC intent therefore records warm reset as its own sequence with its own ranks, and structural analysis checks the warm path separately from the cold path.
The review asks for each power mode transition whether the reset state during and after it matches the intent, and for each warm reset whether its release order is stated and checked. A design whose RDC evidence covers only cold reset is half signed off: the warm and power-transition sequences need their own entries in the coverage questions.
Because cold-reset ordering rides on the power-up sequence, which a warm reset skips. Without its own enforced order, domains can release in an order the design never verified.
Whether post-reset operation is correct with arbitrary retained values meeting freshly reset neighbours: the reset sequence must bring the pair to a consistent state, not assume both started at zero.