By default, when a wide master issues a single-beat transaction to a narrower AXI4-Lite slave, SmartConnect converts the wide transfer to a series of narrow single-beat transactions that span all the address locations in the master's original transfer. If the master 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 overwritten. During downsizing, SmartConnect converts the wide transfer to a series of transactions matching the target slave's data-width. However, SmartConnect suppresses any output transfer in which the WSTRB bits for all byte positions in the transfer are zero. Some control-register slaves do not honor the WSTRB inputs and overwrite any locations that gets accessed. By suppressing null write transfers, SmartConnect 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 slave's physical data width. Then during downsizing, SmartConnect will convert to only one output transaction to the slave, because there are no other locations being accessed by the master. Except for this application, it is recommended that master endpoints do not drive their AWSIZE or ARSIZE outputs with values indicating transfers narrower than the master's physical data width.