Hi All,
I am a bit confused with Exclusive access and Locked access
Would you give me example what scenario master will use exclusive access and Locked access?
Thanks a lot!
Hi Colin, thanks for reply
if Master use non-bufferable write, the performance are usually degraded(because of bresp must be obtained from the final destination)?
Yes, that's definitely true.
But in your question when you were assuming the monitor was in the interconnect, you were concerned that the access hadn't actually reached target S0. If you use a bufferable write, the response for that write transaction can be returned by any intermediate component (such as a write buffer) according to the AXI protocol, so it might not even reach an exclusive access monitor before a non-exclusive response is returned.
The AXI protocol states that you must use AxCACHE encodings that ensure the target monitoring the transactions will actually see the transactions. The obvious concern here would be if the transaction was marked as cacheable, and so was stored in a cache and not accessing the target, so not monitored. But bufferable is also then a concern, and a bufferable transaction could be held in a buffer before the exclusive monitor logic, and so the exclusivity of the access is not tested when a write response is returned to the transaction source.
So yes, non-bufferable transfers might not return as quick a BRESP as a bufferable one, but we want to ensure that it is the final destination S0 target that returns the response, so a small added latency is the penalty you might have to accept. Hopefully exclusive accesses are not a significant number of your transactions, so it shouldn't be a significant performance degradation.