A SCSI target port shall respond to an attention condition with MESSAGE OUT phase as follows:
a.If an attention condition is created during a COMMAND phase, the target shall enter MESSAGE OUT phase after transferring part or all of the command descriptor block.
b.If an attention condition is created during a DATA phase, the target shall enter MESSAGE OUT phase at the target's earliest convenience (for example, on a logical block boundary). The initiator shall continue REQ/ACK handshakes until it detects the phase change.
c.If an attention condition is created during a STATUS phase, the target shall enter MESSAGE OUT phase after the status byte has been acknowledged by the initiator.
d.If an attention condition is created during a MESSAGE IN phase, the target shall enter MESSAGE OUT phase before it sends another message. This permits a MESSAGE PARITY ERROR message from the initiator to be associated with the appropriate message.
e.If an attention condition is created during a SELECTION phase, the target shall enter MESSAGE OUT phase after that SELECTION phase.
f.If SPI (SCSI Parallel Interface) information unit transfers are disabled and an attention condition is detected during a RESELECTION phase, the SCSI target port shall enter MESSAGE OUT phase after the SCSI target has sent its IDENTIFY message for that RESELECTION phase.
g.If an attention condition is created during a RESELECTION phase the target shall enter MESSAGE OUT phase after the target has sent the first Information Transfer phase.
h.If the attention condition is detected during the transfer of a SPI data stream information unit, the target shall terminate the current stream by entering into MESSAGE OUT phase at the end of any SPI data stream information unit in the current stream.
i.If the attention condition is detected between SPI information units, the target shall enter MESSAGE OUT phase at the completion of the next SPI information unit.
During a RESELECTION phase, the initiator should only create an attention condition to transmit an ABORT TASK SET, Abort Task, Target Reset, Clear Task Set, Disconnect, Logical Unit Reset, or NO OPERATION message. Other uses may result in ambiguities concerning the nexus.
The initiator shall keep the ATN signal asserted throughout the MESSAGE OUT phase if more than one byte is to be transferred. Unless otherwise specified, the initiator may negate the ATN signal at any time that does not violate the specified setup and hold times, except it shall not negate the ATN signal while the ACK signal is asserted during a MESSAGE OUT phase. Normally, the initiator negates the ATN signal while the REQ signal is true and the ACK signal is false during the last REQ/ACK handshake of the MESSAGE OUT phase.
5.2Bus reset condition
The bus reset condition is used to create a hard reset (see Section 5.3) for all SCSI devices on the bus and change the bus to a BUS FREE phase. This condition shall take precedence over all other phases and condi- tions. Any SCSI device may create the bus reset condition by asserting the RST signal for a minimum of a reset hold time.
Environmental conditions (for example, static discharge) may generate brief glitches on the RST signal. SCSI devices shall not react to glitches on the RST signal that are less than a reset delay. The manner of rejecting glitches is
5.3Hard reset
A SCSI device detecting a reset event shall release all SCSI bus signals within a bus clear delay of the transi- tion of the RST signal to true, except the RST signal if it is asserting RST. The BUS FREE phase always fol- lows the hard reset condition. The SCSI device shall not assert the RST signal in response to a reset event on the same bus segment.
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