I have some doubts in AXI
->In AXI, Out of order is with respect to transactions or it is with respect of master/slave?
->Out of order can occur in single master/single slave system ot it can occur only in multi master system?
It is in the context of AXI Req<->Rsp.
In-order AXI transaction means: A master must receive its AXI Responses from the slave in the order it issued the AXI Requests.
Out-of-order AXI transaction means: A master could receive its AXI Responses from the slave in any order.
It is topology agnostic: p2p (single master/slave), crossbar, mesh, etc.
I have the same doubt, if a master is giving multiple outstanding request to the same slave, can the response come out of order? If yes how?
An example of out-of-order responses would be a memory controller with cache. It is possible that the controller receives a write request which requires the cache to be written to physical memory, which may require a large number of clock cycles to complete.
After the write request is received, a read request could then be received. If the read request is coming from cache memory that is valid, the controller can immediately provide the read data.
The data phase of the read request would complete prior to the write-request completing, resulting in an out-of-order response.