what is Partial cache line store means? How can a master store partial cache line?
Hi ash11,
When doing a partial cache line store, the master will first need to obtain the "old" full cache line data, to be able to "merge" the "new" partial data.
This is different to a full cache line store for example, where the master does not need the "old" data at all.
See the AMBA AXI and ACE Protocol Specification, "D1.3.4 Channel usage examples", "Store operations for a partial cache line".
But my question is how does it master can transfer partial cache line?Is it legitimate ?can you tell why do we need a partial cache line in a system?
Even though the operation is called "partial cache line store", it is a full cache line, which moves through the interconnect. Here is a summary of the partial cache line store example from the specification:
1. Master asks for "old" cache line with ReadUnique
2. Interconnect relays request
3. Snooped component provides the "old" cache line
4. Interconnect relays "old" cache line
5. Master performs store
Step 5 is where the cache line is partially modified.