The host adapter dequeues on a first in, first out (FIFO) basis for each target/LUNcombination. However, due to the optimization algorithm used by the host adapter, atask may sometimes be started earlier in spite of its late entrance in the queue onmultiple target/LUN systems. Task queuing should not be used where changes in theorder of command execution may cause data integrity failures.Enhanced Mode FirmwareThe Enhanced Mode is an interface architecture which allows the AHA-1740A/1742A/1744 to take full advantage of the EISA bus facilities. It utilizes a dis-tinct hardware interface control logic, implemented in the AIC-575 device. Thispermits features such as full 32-bit addressing and the entire EISA register set to beused. This mode is not compatible with older versions of the ASW-1400 series of soft-ware managers.The following levels of manager revision are capable of operating with the AHA-1740A/1742A/1744 in Enhanced mode:• ASW-1410 v3.0 and later (ASPI DOS Manager)• ASW-1420 v1.3 and later (LADDR SCSI Support for OS/2® )• ASW-1440 v3.0 and later (ASPI Manager for Novell NetWare ® )• ASW-1450 v1.0 and later (SCSI Manager for SCO UNIX® and Open Desktop)In order to use the Enhanced Mode, the AHA-1740A/1742A/1744 must be correctly re-configured. Use the EISA Configuration Utility (EISA) that came with your EISA sys-tem and the EISA configuration files on the ASW-C174 diskette provided with theAHA-1740A/1742A/1744. The AHA-1740A/1742A/1744 are not capable of simultane-ous operation in Standard and Enhanced Modes.The firmware in this mode uses a different architecture to the Standard Mode. Thefirmware is interrupt driven by events on the host and SCSI side. It uses only a sin-gle mailbox, unlike the Standard Mode which uses up to 255. This does not result inany bottleneck or performance impairment, due to the fast processor used on theAHA-1740A/1742A/1744 and the servicing algorithm used.EISA-to-Fast SCSI Host Adapter Architecture2-9
