Scsi host adapter with shared command and data buffer

Abstract

A small computer system interface (SCSI) controller circuit, connected between a host computer bus and a SCSI bus, includes a storage buffer shared between command and data signals provided by a host computer to a target SCSI peripheral device. The shared buffer includes a bidirectional FIFO which is used for intermediate storage of command blocks between transferred the host and the target device as well as data blocks. In the case of data transfers from the host to the target device, a command block is written to the bidirectional FIFO followed by as much of the data block as will fit in the remaining FIFO space. After the target device has read the command block, it accesses the SCSI bus and begins the transfer of data from the FIFO. In the case of data transfers from the target device to the host, a data transfer command block is first written to the FIFO by the host. The command block is read by the target device which then provides the requested data to the FIFO over the SCSI bus. The host system receives the requested data from the same shared storage buffer to which the command block was written.