The Unabridged Pentium 4 IA32 Processor Genealogy

Non-Memory Transactions Have a Snoop Phase

All transactions, including non-memory transactions, have a Snoop Phase. For non-memory transactions, however, there are only three valid snoop responses:

1. A snoop miss (HIT# and HITM# both deasserted).

2. Defer (DEFER#) asserted, indicating that the currently-addressed target will issue a Retry or a Deferred response in the transaction's Response Phase. In this case, the snoop result is irrelevant (unless HITM# is asserted, cancelling the deferral).

3. A snoop stall (HIT# and HITM# both asserted), indicating that the Snoop Phase is to be extended by two clocks. A non-memory Response Agent is permitted to stall the snoop response to give itself more time for internal operations to complete before presenting a ...