The description in the Spec is a little vague on this. The requirements for a pair exclusive access are same id, same length, transaction can't be cacheable and control signals must be identical. Does this imply AWPROT and ARPROT have to be same for EA read and EA write? What if the AWPROT and ARPROT are different, should the device should return OKAY instead of EXOAKY?
Does anyone out there have any comments on this?
Hey Ting, I am moving this to the ARM Processors section where the AMBA content and people will be lurking.
I'm not sure on the requirements for all of the bits, but I strongly suspect that you would want them to be identical. The AR/WPROT bit proves the isolation signals for the Security Extensions (a.k.a. TrustZone in the ARM products) so if those bits differ it is highly likely that the slave will treat them as totally separate accesses (or reject one of them). In some implementations transactions with different PROT bits may even get sent to totally different slaves ...
Hello tqu. Has your question been addressed by Pete or is there any more precision you need?
If you are OK, would you please be able to mark the correct answer?
I have another question. As for Exclusive access in AXI4, my understanding is as follows :
1. Exclusive access is used to issue non-Cacheable requests on Read/Write channels.
2. Exclusive access is basically carried out in a pair of Read and Write transactions, having same ID and same control information.
3. For an exclusive Read/Write pair issued on channel, the response will be EXOKAY for both read and write transactions iff no other master performed a store to that location prior to the write transaction
Is that correct?
If yes, then :
1. This can be done in the case of a Non-cacheable store request coming from core to cache, but what should be done for a non-cacheable read request? Should that also be issued as exclusive? If yes, then do we need to issue a write transaction for a non-cacheable read request coming from core?
2. Can someone please explain the significance of AWREGION/ARREGION signal?