[BUG] <AXI response signals are not supported in all access modes>

[AEzzejjari]

Is there an existing CVA6 bug for this?

• [X] I have searched the existing bug issues

Bug Description

The master can know the status of a transaction by decoding the response information from the subordinate in the response signal X_RESP.

This signal is supported by the CVA6 in exclusive mode, where it must be equal to EXOKAY (x_resp = '01) to indicate that the transaction has passed. In another access mode, it can be equal to any value. So we can inject errors and CVA6 does nothing. The specification says that the EXOKAY can only be given in response to an exclusive read or write.

My point is that we have a signal that is only supported in one access mode, not in the others, and I think this is a bug.