Scsi Hard Reset Option; Eisa Expansion Identifiers - Adaptec AHA-1740A Technical Reference Manual

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The SCSI Soft Reset option is useful in multitasking systems that cannot tolerate the
overhead of a complex reconfiguration and reinitialization after a normal reset opera-
tion. For the SCSI Soft Reset option to operate correctly, all SCSI devices that com-
municate on the SCSI bus must support the Soft Reset option. If any SCSI devices
support the Hard Reset option, it is likely that operations will be terminated without
warning and the system will have to time out and monitor the requirement to restart
some activities.

SCSI Hard Reset Option

The Hard Reset option is designed to restore all attached SCSI devices, including
both hosts and peripheral devices, to their power-on reset state. All system activities
that have not been recorded on a nonvolatile memory device or through another SCSI
path are completely lost and must be restarted. The system must be completely reini-
tialized. For certain types of systems that frequently do back-up or check point their
transactions, that reinitialize quickly and easily, or that infrequently do resets, the
Hard Reset option is appropriate. The AHA-1740A/1742A/1744 responds to a SCSI
Reset condition by executing only the Soft Reset option, but it notifies the host when-
ever a SCSI Reset condition has been established by causing an interrupt to the host.
The host then has the option of converting the Soft Reset to a Hard Reset by forcing
the host adapter to clear all the ongoing operations and return to its initial state. The
host requests this by raising the SRST bit (bit 6 of the Host Adapter Control Port).
The host must raise the SRST bit within 300 microseconds to disable the restarting
of operations according to the rules of Soft Reset. The raising of the SRST bit causes
the host adapter to abandon all CCBs and prepare itself to begin accepting new in-
structions from the host. No secondary SCSI Reset signals are activated. The mailbox
initialization and all normal SCSI initial conditions are reset by the SRST bit, so that
reinitialization is required to restart the system. Of course the system still has the
right at any time that the IDLE bit (bit 4 of the Host Adapter Status Port) is on to
execute any of the adapter commands and modify the mailbox address or the SCSI in-
itial conditions.
If the host requires that the SCSI be reset according to the SCSI Hard Reset option,
the host raises the HRST bit. The host adapter will then set a SCSI Reset condition
on the SCSI Bus and clear all its CCB and status information, thus performing a
SCSI Hard Reset with a single load to the Host Adapter Control Port. Reinitializa-
tion will be required.

EISA Expansion Identifiers

Expansion board identifiers is a term used in the EISA specification for the parame-
ters used to integrate an add-in card into an EISA host system. These identifiers are
used by the system ROM during configuration to recognize the information provided
in the configuration file. The configuration file is provided as a part of the system soft-
ware or in the separate ASW-C174 Configuration software package.
This automatic configuration eliminates the need for switches or jumpers and re-
places them with programmable registers. It also resolves conflicts between system
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AHA-1740A/1742A/1744