Reset Functions; Hard Reset Operations - Adaptec AHA-1740A Technical Reference Manual

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Mailbox In entries, so the host should check the next entry to determine if more than
one set of information has been provided. The MBI entries are filled in round-robin
order, so the host should simply check the next MBI entry after the last one that was
found when a new MBIF interrupt occurs.
If an MBIF interrupt is set and other Mailbox In entries are made before the inter-
rupt is cleared, then all the entries can be scanned as found. The new MBIF inter-
rupt will be presented if the SCRD and HACC interrupts are cleared. A new MBIF
interrupt will be presented regardless of the state of the MBOA interrupt bit. It is im-
portant to clear and record each interrupt as soon as possible to avoid the possible ac-
cidental resetting of a valid interrupt. In addition, it is desirable to enable the MBOA
interrupt as rarely as possible. The host system software must be ready to scan for
MBI entries even if no MBIF interrupt occurred.

Reset Functions

The reset functions provided by the AHA-1740A/1742A/1744 are extensive to allow
the fullest flexibility and architectural consistency, both with SCSI and with the In-
dustry Standard Architecture.

Hard Reset Operations

Resets may be generated by the hardware through two mechanisms. The RESET sig-
nal from the ISA socket is generated by the system board to reset or initialize all in-
stalled adapters upon power-on or during a low line voltage condition. The system
can also activate this signal under host program control. In addition to the RESET
signal, the setting of the HRST bit (bit 7 of the Host Adapter Control Port) will force
a hardware reset to the AHA-1740A/1742A/1744. Regardless of the source, a Hard Re-
set forces the following actions on the AHA-1740A/1742A/1744.
All internal registers of the AHA-1740A/1742A/1744 are returned to their re-
set condition.
The host adapter's microprocessor returns all internal information and pa-
rameters to their initial state.
The host adapter performs all required internal diagnostics.
A standard SCSI Reset condition is generated to all other attached SCSI
devices.
During the Hard Reset process, the AHA-1740A/1742A/1744 will indicate to the at-
tached host that self-testing is in process by raising the STST bit in the Host Adapter
Status Port. After the Hard Reset process is complete, the AHA-1740A/1742A/1744
will indicate that initialization parameters are required from the host by raising the
INIT bit in the Host Adapter Status Port.
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AHA-1740A/1742A/1744