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APB5 adds optional wake-up signaling and user-defined metadata around the baseline APB transfer model.

PWAKEUP wake-up signaling

PWAKEUP is an optional APB5 signal used to indicate APB-related activity to clock or power control logic. It must be glitch-free and suitable for asynchronous sampling by another clock domain.

Important guidance:

  1. PWAKEUP can be asserted before, during, or after PSELx.
  2. It is recommended to assert PWAKEUP at least one cycle before PSELx to avoid delaying the transfer.
  3. If PWAKEUP and PSELx are HIGH in the same cycle, PWAKEUP must remain asserted until PREADY is asserted.
  4. If a Completer waits for PWAKEUP before asserting PREADY, the system can deadlock if PWAKEUP is never asserted.

User signals

APB5 defines optional user signals:

SignalSourceMeaning
PAUSERRequesterUser-defined request attribute
PWUSERRequesterUser-defined write data attribute
PRUSERCompleterUser-defined read data attribute
PBUSERCompleterUser-defined response attribute

The APB protocol does not define what these user bits mean. Because of that, the specification generally recommends avoiding user signaling unless the system has a controlled and documented use for it.

RME Support compatibility

Compatibility between Requester and Completer interfaces depends on the RME_Support property on each side.

Requester RME_SupportCompleter RME_SupportCompatibility
FalseFalseCompatible
FalseTrueCompatible. Tie the PNSE input LOW.
TrueFalseNot compatible
TrueTrueCompatible

APB Protocol