In a transfer controller with hub and ports architecture one of the data ports
is an active data port. This active data port can supply its own source information,
destination information and data quantity in a data transfer request. This data
transfer request is serviced in a manner similar to other data transfer requests.
The active data port may specify itself as the data destination in an active read.
Alternatively, the active data port may specify itself as the data source in an
active data write.