Host adapter reset conditions are initiated from two different vantage points: the host system and the SCSI bus. A description of each follows.
Host-Initiated Reset Operations
The host system may reset the host adapter to an initial power-on condition through two different operations, one system and the other software.
System Reset-The host adapter is fully reset and initialized to a power-on initial condition when the Reset signal is true on the host system bus. The Reset signal is asserted to a true condition by the host (1) during power on, (2) host detected low-power conditions, or (3) a user-invoked reset switch reset. The Reset signal is ap-plied universally to all installed host adapters in the system bus. A host adapter system reset causes a power-on initialization process which also results in a reset of all the devices on the SCSI bus.
Software Reset-The host adapter may be fully reset to an initial state by a software command, just the same as if a system reset had been received by setting the Hard Reset bit (RHARD). When RHARD is set to true, a Reset condition occurs imme-diately. However, this Reset condition 'Yill only affect one host adapter, unlike the system reset (described above) which resets all host adapters installed in the system bus. An RHARD reset may issue a subsequent reset to the SCSI device de-pending on the AutoSCSI utility configuration setting for the Enable SCSI Bus Re-set option (see the manual for your host adapter for more information).
Either type of host-initiated reset will cause the following conditions on the host adapter.
• The control registers of all intelligent logic modules on the host adapter will be initialized to a known state.
• All pending operations are aborted and all data structures are initialized to a no operation pending state.
• The host adapter executes all internal diagnostic functions. While the diagnos-tic functions are in process, the host adapter will indicate this condition by set-ting the Diagnostic Active bit (DACT) to true in the Status Register.
• During a system reset, the host adapter places a SCSI Bus Reset condition on the SCSI bus. This may also occur during a software reset (using the RHARD bit) , but depends on the AutoSCSI utility configuration setting for the Enable SCSI Bus Reset option. This will reset all peripheral devices, whether a target or ini-tiator.
• ~ter completion of a system reset, the host adapter indicates that it is now in an initial condition by asserting the Initialization Required bit GNREQ) in the host adapter's Status Register. This condition requires that all mailbox, com-mand control blocks, and host adapter operation parameters be established be-fore operations may begin.
Note: The host mqy intiate a soft reset by setting the RSOFT bit. This reset reinitializes the specific host adapter, but there is no subsequent SCSI bus reset.
SCSI Bus Reset Operations
The SCSI Bus Reset condition is used to clear all SCSI devices immediately from the SCSI bus. When the SCSI bus Reset signal is asserted, the SCSI Bus Reset con-dition takes precedence over all other bus phases. A SCSI Bus Reset condition may be forced by any device on the bus, whether a target or initiator. Whenever a SCSI Reset condition occurs, a Bus Free phase always follows the Reset condition.
The five ways in which a SCSI bus reset may be either asserted or sensed by the host adapter are as follows:
Rl The SCSI Bus Reset condition is always asserted when the host adapter is re-set by the host system (host system system rere-set only). This is described ear-lier in this section under the heading "Host-Initiated Reset Operation."
R2 The SCSI Bus Reset condition may be asserted when the host adapter is soft reset by the host system when RHARDis set to true (depending on the Au-toSCSI utility configuration setting for the Enable SCSI Bus Reset option).
This is also described under the heading "Host-Initiated Reset Operations."
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R3 The SCSI Bus Reset condition is asserted if the Reset SCSI Bus bit (RSBUS) is set by the host system control software.
R4 The host adapter may initiate a SCSI Bus Reset condition in reaction to
a
detected bus phase error. The host adapter constantly monitors the SCSI bus for invalid conditions. If an invalid phase is detected, the host adapter will perform a normal SCSI Bus Reset operation which includes the asser-tion of the SCSI bus Reset signal.
R5 The host adapter will detect and respond to a SCSI Bus Reset condition that is asserted by another device on the bus. Other SCSI devices may normally assert the Reset signal during either initialization or certain error recovery states. The device driver requires an acknowledgement from the host adapter that a SCSI Reset operation has taken place, so the SCSI Reset State bit is set in the interrupt register.
While the SCSI specification defines two methods by which the SCSI bus may be reset, either by the hard reset option or the soft reset option,
BusLogic host adapters only support the hard reset option.
The SCSI bus hard reset option restores ALL SCSI devices, target or initiator, to the initial power-on condition. All system activity is lost, and all devices must be com-pletely reinitialized before normal operations may be restored. SCSI devices that implement the hard reset option perform the following operations:
• Clear all uncompleted commands.
• Release all SCSI device reservations.
• Return any SCSI device operating modes to their default condition.
Here is how the host adapter implements a SCSI hard reset:
• When the host adapter detects a SCSI reset, it issues an interrupt indicating a SCSI reset has occurred to the host system.
• The host adapter sets both the SCSI Reset State bit (RSTS) and the Interrupt Val-id bit (INTV) in the host adapter's Interrupt Register.
• All host adapter command control blocks (CCBs) are abandoned and the host adapter readies itself to accept new initialization commands.
• BusLogic recommends that after the device driver receives the RSTS, it issue a RHARD or an RSOFf to ensure that the host adapter is re-initialized.
• All the mailbox and command control blocks must be reinitialized.
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