Avago Technologies LSI53C896 User Manual
Page 138
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Registers
Version 3.3
Copyright © 1998–2003 by LSI Logic Corporation. All rights reserved.
data received for odd parity. This bit is used for diagnostic
testing and is cleared for normal operation. It is useful to
generate parity errors to test error handling functions.
IARB
Immediate Arbitration
1
Setting this bit causes the SCSI core to begin arbitration
immediately when a Bus Free phase is detected following
an expected SCSI disconnect. This bit is useful for
multithreaded applications. The ARB[1:0] bits in
are set for full arbitration
and selection before setting this bit.
Arbitration is retried until won. At that point, the
LSI53C896 SCSI function holds SBSY and SSEL
asserted, and waits for a select or reselect sequence.
The Immediate Arbitration bit is cleared automatically
when the selection or reselection sequence is completed,
or times out.
An unexpected disconnect condition clears IARB with it
attempting arbitration. Refer to the SCSI Disconnect
Unexpected bit (
, bit 7) for
details about expected versus unexpected disconnects.
It is possible to abort an immediate arbitration sequence.
First, set the Abort bit in the
Interrupt Status Zero (ISTAT0)
register. Then one of two things eventually happens:
•
The Won Arbitration bit (
bit 2) is set. In this case, the Immediate Arbitration bit
must be cleared. This completes the abort sequence
and disconnects the chip from the SCSI bus. If it is not
acceptable to go to Bus Free phase immediately
following the arbitration phase, it is possible to
perform a low level selection instead.
•
The abort completes because the LSI53C896 SCSI
function loses arbitration. This is detected by the
clearing of the Immediate Arbitration bit. Do not use
the Lost Arbitration bit (
bit 3) to detect this condition. In this case take no
further action.
SST
Start SCSI Transfer
0
This bit is automatically set during SCRIPTS execution
and should not be used. It causes the SCSI core to begin
a SCSI transfer, including SREQ/ and SACK/