Hello everyone,
Can any one explain me why there is a case where a start state in Unique Dirty leads to a final state in Unique Dirty for a readClean transaction in ACE protocol.
This transaction requires a clean copy of the data, so how it can possible to have the (UD-UD) transition possible?
Thanks,
Anya ka,
Hi Anya,
This transition is a 'permitted' transaction, as opposed to 'expected' transaction. This generally means that its a less efficient, or an unexpected use of a transaction. In the case of a ReadClean, its clear that it not efficient to issue this transaction when the master already has the data.
If the line starts in a Dirty state, and the transaction does not transfer this Dirty responsibility in some way (for example, by writing the data back to memory) then the line must finish in a Dirty state. Otherwise, the Dirty responsibility would have been lost.
Regardless of the RRESP information indicating that PassDirty is not asserted, the Dirty responsibility cannot be lost.