Section 5
SCSI Programming Guidelines
MESSAGE PARITY ERROR
098
- This message is sent from the initiator to the ProDrive
to
indicate that one or more bytes in the last message it received had a parity error.
To indicate its intent to send this message, the initiator must assert
ATN
prior to releasing ACK for
the REQ/ACK handshake
of
the message that has the parity error. This provides an interlock so the
ProDrive can determine which message has the parity error.
LINKED COMMAND COMPLETE
OAH
- This message
is
sent from the ProDrive to an initiator
to indicate that the execution
of
a linked command has been completed and status has been sent. The
initiator must then set the pointers to the initial state for the next linked command. Refer also to
Sections 5.7.1.8 and 5.7.1.9.
LINKED COMMAND COMPLETE (WITH FLAG)
OBH
- This version
of
the LINKED
COMMAND
COMPLETE message is used when the flag bit
of
the command is set to one. Refer
also to Sections 5.7.1.8 and 5.7.1.9. .
BUS DEVICE RESET
OCH
- This message is sent from an initiator to direct the ProDrive to clear
all current commands. This message forces the drive to an initial state with no operations pending for
any initiator.
Upon recognizing this message, the ProDrive will go to the BUS FREE phase.
This message does not affect MODE
SELECT command parameters.
IDENTIFY 80H - FFH - These messages may be either sent from or received by the ProDrive
to
establish the physical path connection between an initiator and the drive.
Bit 7 - This bit is always set to one to distinguish an IDENTIFY message from the other messages.
Bit 6 - This bit is set to one only by the initiator. When set to one, it indicates that the initiator has
the ability to accommodate disconnection and reconnection.
It also indicates that the SAVE DATA
POINTER, RESTORE POINTERS and DISCONNECT messages are supported by the initiator.
Bits 5-3 - Reserved; must
be
set to zero.
Bits
2-0 - These bits specify a logical unit number (LUN)
in
a target. For the ProDrive, the only
valid
LUN is zero.
When an IDENTIFY message
is
sent from the ProDrive
to
an initiator during reconnection, an
implied RESTORE POINTERS message must
be performed by the initiator prior to completion
of
this message.
5.6.3
MESSAGE
ERROR
RECOVERY
STRATEGY
5.6.3.1
parity
ErrQrs
During Message phase
Parity is an SCSI option. This section is relevant only
if
the parity option is enabled.
If
the initiator detects a parity violation as the ProDrive transfers a message byte to it, it should ignore
that message and immediately assert
ATN
(before releasing ACK on the offending byte). The initiator
should continue receiving and ignoring bytes until the
ProDrive requests a MESSAGE OUT byte. At
that point, the initiator should send a MESSAGE
PARITY ERROR message; the ProDrive will abort the
command and release the bus. The sense key will
be
set to ABORTED COMMAND
(OBH)
and the sense
code set to
Parity error on the SCSI bus (47H).
If
the ProDrive detects a parity error during a MESSAGE OUT phase, it will continue to request
MESSAGE
OUT
bytes until the initiator deasserts ATN. This procedure should guarantee that the
initiator transfers the entire message containing the parity error. The current command will be terminated,
SCSI
Programming
Guidelines
5-13
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