Downsizing to an AXI4-Lite Slave - Downsizing to an AXI4-Lite Slave - 1.0 English - PG453

By default, when a wide SI issues a single-beat transaction to a narrower AXI4-Lite MI, AXI Switch converts the wide transfer to a series of narrow single-beat transactions that span all the address locations in the original transaction. If the master device intends to write to only one location in the slave without disturbing adjacent locations, there are two alternatives:

1. During the master's write data transfer, disable all WSTRB bits for byte locations not to be written. During downsizing, AXI Switch converts the wide transfer to a series of transactions matching the MI data-width. However, AXI Switch suppresses any output transfer in which the WSTRB bits for all byte positions in the transfer are zero. Some control-register slaves can choose not honor the WSTRB inputs and overwrite any locations that gets accessed. By suppressing null write transfers, AXI Switch writes only to locations where the WSTRB bit-string is non-zero for each output word.
2. During the master's write address transfer, drive a value onto the AWSIZE output that corresponds to the MI physical data width. Then during downsizing, AXI Switch convert to only one output transaction to the MI, because there are no other locations being accessed by the transaction.