Host adapter having a snapshot mechanism

Abstract

A circuit collects data from a number of locations in a system memory of a personal computer, and can refetch the collected data at any time, e.g. when an adapter for transferring data between a computer bus and a peripheral bus that includes the circuit encounter an unexpected event (such as an error) in the transmission (or retransmission) of data to a first peripheral device. So the adapter simply flushes the data on encountering the unexpected event. Thereafter, the adapter switches context, to transfer data to a second peripheral device. At a later time, the circuit in the adapter refetches the flushed data, for retransmission of the data to the first peripheral device. To refetch the flushed data, the circuit does not traverse backwards through a scatter/gather data transfer pointer list (described above) that is used to collect the data from system memory. Instead, the circuit initially stores the values (collectively called “snapshot”) of signals in various registers at the time of initial receipt of the data, and at a later time loads the saved snapshot to refetch data that was flushed.