Reference no: EM131986393

Problem

Many snooping coherence protocols have additional states, state transitions, or bus transactions to reduce the overhead of maintaining cache coherence. An optimization to the MSI snooping protocol is to add the Exclusive (E) state, indicating that no other node has a copy of the block, but the block has not yet been modified. A cache block enters the Exclusive state when a read miss is satisfied by memory and no other node has a valid copy. CPU reads and writes to that block proceed with no further bus traffic, but CPU writes causes the state of the block to transition from Exclusive to Modified. There is a Shared wire on the bus that signals '1' when a read miss appears on the bus and at least one other processor has a copy of the block. Otherwise, the Shared wire signals '0', indicating that the block is exclusively read by one processor. Draw state transition diagrams for the MESI cache coherence protocol. Two diagrams are needed: first diagram should be based on requests from the processor and the second diagram should be based on requests from the bus.