3.5. SCSI-bus Phase Sequences
3.5.1.2. Disconnects/Reconnects
Disconnection is the process of go~ng through two MESSAGE-OUT phases and then to the BUS FREE phase in: the middle of a command execution. When the Drive bas disconnected, it will always try to reconnect·at a later time. Reconnection is the process of going from the BUS -FREE phase·to the ARBITRATION phase, RESELECTION and MES-SAGE-IN phase.
When disconnecting the first of the two messages transferred will be a SAVE DATA POINTER message. The second message will be a DIS-CONNECT message. The Drive will then enter the BUS FREE phase.
When reconnecting the message transferred will be a IDENTIFY mes-sage with the Disconnect Granted bit (Bit 6) set to zero. The three LUN bits will also be set to zero.
All commands except INQUIRY, REQUEST SENSE and TEST UNIT READY may disconnect if disconnection is granted by the Initiator.
The following shows if and when the various commands discon-nects/reconnects during execution. Only the normal execution is shown.
It is assumed that the Initiator selects the Drive with ATN asserted so that disconnection can be granted (with the IDENTIFY message).
The term 'immediate type command' means commands with the·JMM bit set in the Command Descriptor Block (CDB). The WRlTEFlLE-MARKS command is an exception here •. It is not regarded as an Immedi-ate type command even if its IMM bit is set.
Please refer to the section on the MODE SELECT command for details on the Read Buffer Full and Write Buffer Empty Ratios.
COpy
:= <initiator-part> <message-out> <command> <data-out> <disconnect>
<reconnect> <completed>
This sequence will be used when the COPY command does not follow an Immediate type command. As soon as the COPY Parameter List has been transferred the Drive will disconnect. The Drive will reconnect when the copy operation has terminated. Note that the COPY command will not execute if disconnection has not been granted.
:= <initiator-part> <message-out> <command> <disconnect>
<reconnect> <data-out> <disconnect> <reconnect> <completed>
This sequence will be used when the COPY command follows an immediate type command. The Drive will disconnect the first time when the CDB has been transferred. The Drive will reconnect the first time when the previous Immediate type command has completed execution.
As soon as the COPY Parameter List has been transferred the Drive will disconnect the second time. The Drive will reconnect the second time when the copy operation has terminated. Note that the COPY com-mand will not execute if disconnection has not been granted.
3-14 SCSl-2 Functional SpecifICations
·".-__ " r '
<sequence 7>
<sequenceS>
<sequence 4>
<sequence 7>
ERASE
:=< initiator-part> <message-out> <command> <disconnect> <reconnect>
<completed>
The Drive will disconnect when the CDB has been transferred. The Drive will reconnect when the tape is positioned back at BOT (or when an error has been detected) if the IMM-bit is not set. If the IMM-bit is set, the Drive reconnects immediately.
This sequence will also be used when the ERASE command follows an Immediate type command. The Drive will disconnect when the CDB has been transferred. If the IMM bit is set, the Drive will reconnect when the previous Immediate type command has completed execution. If the IMM bit is not set the Drive will reconnect when both the previous com-mand and ,the ERASE comcom-mand has completed execution.
INQUIRY
:= <initiator-part> <message-out> <command> <data-in> <completed>
The Drive will never disconnect when executing this command.
LOADJUNLOAD
:= <initiator-part> <message-out> <command> <completed>.
This sequence will be used when the IMM bit is set and the LOADIUN-LOAD command follows a non-Immediate type command other than a COPY, READ, VERIFY, SPACE, SEEK BLOCK, WRITE or WRITE FILEMARKS command.
:= <initiator-part> <message-out> <command> <disconnect>
<reconnect> <completed>
This sequence will be used when the IMM bit is not set. The Drive will disconnect when the CDB has been transferred. The Drive will recon-nect when the tape is positioned at BOT or EOT (or when an error has been detected).
This sequence will also be used when the LOADIUNLOAD command fol-lows an Immediate type command. The Drive will disconnect when the CDB has been transferred. If the IMM bit is set the Drive will reconnect when the previous Immediate type command has completed execution.
If the IMM bit is not set the Drive will reconnect when both the previ-ous command and the LOADIUNLOAD command has completed execu-tion.
This sequence will also be used when the IMM bit is set and the LOADIUNLOAD command follows a COPY, READ, VERIFY ,sPACE, SEEK BLOCK, WRITE or WRITE FILEMARKS command. The Drive will disconnect when the CDB has been transferred. The Drive will re-connect as soon as the previous command has terminated (read/space operation stopped or data flushed from the data buffer) and the actual LOADIUNLOAD command has started execution.
3-15 SCSl-2 Functional Specifications
<sequence 7>
<sequence 5>
<sequence 8>
<sequence 10>
<sequence 11 >
Tandberg Data Logical Characteristics
LOCATE
:= <initiator-part:> <message-out> <command> <disconnect>
<reconnect> <completed>
The Drive will disconnect when the CDB has been transferred. 'l1le Drive will reconnect when the specified block has been located (or an er-ror has been detected).
This sequence will also be used when the LOCATE command follows an Immediate type command. 'l1le Drive will disconnect when the CDB has been transferred. The Drive will reconnect when both the previous com-mand and the LOCATE comcom-mand has completed execution.
This sequence will also be used when the LOCATE command follows a command other than COPY (restore), READ, SPACE, VERIFY or LO-CATE.
LOG SENSE
:= <initiator-part> <message-out> <command> <data-in> <completed>
This sequence will be used when the LOG SENSE command does not follow an Immediate type command.
:= <initiator-part> <message-out> <command> <disconnect>
<reconnect> <data-in> <completed>
This sequence will be used when the LOG SENSE command follows an Immediate type command. 'l1le Drive will disconnect when the CDB has been transferred. The Drive will reconnect when the previous Immedi-ate command has completed execution.
MODE SELECT
:= <initiator-part> <message-out> <command> <data-out> <disconnect>
<reconnect> <completed>
This sequence will be used when the MODE SELECT command does not follow an Immediate type command. The Drive will disconnect when the Parameter List has been transferred and then reconnect when the parameters have been saved.
:= <initiator-part> <message-out> <command> <disconnect>
<reconnect> <data-out> <disconnect> <reconnect> <completed>
This sequence will be used when the MODE SELECT command follows an Immediate type command. The Drive will disconnect the first time when the CDB has been transferred. The Drive will reconnect the first time when the previous Immediate type command has completed execu-tion. The Drive will disconnect the second time when the Parameter List has been transferred. The Drive will reconnect the second time when the parameters have been saved.
3-16 SCSl-2 Functfonal Specificotfons
<sequence 5>
<sequence 8>
<sequence 4>
<sequence 7>
<sequence 4>
<sequence 7>
MODESENSE.
:= <initiator-part> <message-out> <command> <data-in> <completed>
This sequence will be used when the MODE SENSE command does not follow an Immediate type command.
:= <initiator-part> <message-out> <command> <disconnect>
<reconnect> <data-in> <completed>
This sequence will be used when the MODE SENSE command follows an Immediate type command. The Drive will disconnect when the CDB has been transferred. The Drive will reconnect when the previous Immediate command has completed execution.
PREVENT/ALLOW MEDIA REMOVAL
:= <initiator-part> <message-out> <command> <completed>.
This sequence will be used when the PREVENT/ALLOW MEDIA RE-MOVAL command follows a non-Immediate type command.
:= <initiator-part> <message-out> <command> <disconnect>
<reconnect> <completed>
This sequence will be used when the PREVENT/ALLOW MEDIA RE-MOV AL command follows an Immediate type command. The Drive will disconnect when the CDB has been transferred. The Drive will recon-nect when both the previous command and the PREVENT/ALLOW ME-DIA REMOVAL command has completed execution.
READ
:= <initiator-part> <message-out> <command> <completed>
This sequence will be used when a READ command specifying a zero transfer length follows a COPY (restore), READ,VERIFY, SEEK BLOCK (with the IMM bit set to zero) or SPACE command.
:= <initiator-part> <message-out> <command> <disconnect>
<reconnect> <completed>
This sequence will be used when a READ command specifying a zero transfer length follows a command other than COPY(restore), READ, VERIFY, SEEK BLOCK or SPACE.
The Drive will disconnect when the CDB has been transferred. The Drive will reconnect when an error has been detected or when the tape has been prepared for read operations (the previous command has terminated, the reference burst has been located and at least on block of data has been read from the tape.
3-17 SCSI-2 Functional Specifications
<sequence 5>
<sequence 8>
<sequence 12>
<sequence 13>
Tandberg Data Logical Choroctertstfcs
:= <initiator-part> <message-out> <command> <data-in> <completed>
This sequence will be used when the'previous command was not an im-mediate type command and the number of bytes requested for transfer is av:ailable in the data buffer and when at the same time the number of bytes requested for transfer is less or equal to the number of bytes speci-fied by the Read Buffer Full Ratio.
:= <initiator-part> <message-out> <command> <disconnect>
<reconnect> <data-in> <completed>
This sequence will be used when the number of bytes requested for transfer is not available in the data buffer and when at the same time the number of bytes requested for transfer is less or equal to the number of bytes specified by the Read Buffer Full Ratio. The Drive will discon-nect when the CDB has been transferred. The Drive will, recondiscon-nect when the requested amount of data are ready for transfer.
:= <initiator-part> <message-out> <command>{<disconnect>
<reconnect> <data-in>}<completed>
This sequence will be used when the number of bytes available for transfer in the data buffer at the time the READ command was issued is less than the number of bytes specified by the Read Buffer Full Ratio and at the same time the total number of bytes transferred is larger than the number ofbytes specified by the Read Buffer Full Batio.
The Drive will disconnect when the number of data bytes ready for transfer in the data buffer is less than the number of bytes specified by the Read Buffer Full Ratio. The Drive will also disconnect to make sure that the burst size·never exceeds the number of bytes specified by the Read ButTer Full Ratio. The Drive will reconnect when the number of bytes ready for transfer is equal to or larger than the' Read Buffer Full Ratio.
:= <initiator-part> <message-out> <command> <data-in> «disconnect>
<reconnect> <data-in>) <completed>
This sequence will be used when more data than specified by the Read Buffer Full Ratio is available in the data buffer and at the same time the total number of bytes transferred is larger than the number of bytes set up by the Read Buffer Full Ratio.
The Drive will disconnect when the number of data bytes ready for transfer in the data buffer is less than the number of bytes specified by the Read BUffer Full Ratio. The Drive will also disconnect to make sure that the burst size never exceeds the number of bytes specified by the Read Buffer Full Ratio. The Drive will reconnect when the number of bytes ready for transfer is equal or larger than the Read Buffer Full Ra-tio.
3-18 SCSl-2 Functional SpecifICations
<sequence 5>
:= <initiator-part> <message-out> <command> <data-in> <completed>
This. sequence will be used when the READ BLOCK LIMITS command does not follow an Immediate type command.
:= <initiator-part> <message-out> <command> <disconnect>
<reconnect> <data-in> <completed>
This sequence will be used when the READ BLOCK LIMITS command follows an Immediate type command. The Drive will disconnect when the CDB has been transferred. The Drive will reconnect when the previ-ous Immediate command bas completed execution.
READ BUt:=FER
:= <initiator-part> <message-out> <command> <completed>
This sequence will be used when the READ BUFFER command does not follow an Immediate type command and the specified transfer length is zero.
:= <initiator-part> <message-out> <command> <disconnect>
<reconnect> <completed>
This sequence will be used when a READ BUFFER command specifying a zero transfer length follows an Immediate type command.
:= <initiator-part> <message-out> <command> «data-in> <disconnect>
<reconnect» <completed>
This sequence will be used when the READ BUFFER command does not follow an Immediate type command.
:= <initiator-part> <message-out> <command> <disconnect>
<reconnect> «data-in> <disconnect><reconnect>) <completed>
This sequence will be used when the READ BUFFER command follows an Immediate type command.
READPOSmON
:= <initiator-part> <message-out> <command> <data-in> <completed>
This sequence will be used when the READ POSITION command does not follow an Immediate type command.
:= <initiator-part> <message-out> <command> <disconnect>
<reconnect> <data-in> <completed>
This sequence will be used when the READ POSITION command fol-lows an Immediate type command. The Drive will disconnect when the CDB bas been transferred. The Drive will reconnect when the previous Immediate command has completed execution.
3-19 SCSI-2 Functional SpeciflCatfons
<Sequence 4>
<sequence 7>
<sequence 5>
<sequence 4>
<Sequence 7>
<sequence 4>
<sequence 7>
Tandberg Data Logical Characteristics
RECOVER BUFFERED DATA
<To Be Supplied>
RELEASE UNIT
:= <initiator-part> <message-out> <command> <completed>.
This sequence will be used when the RELEASE UNIT command follows a non-Immediate type command.
:= <initiator-part> <message-out> <command> <disconnect>
<reconnect> <completed>
This sequence will be used when the RELEASE UNIT command follows an Immediate type command. The Drive will disconnect when the CDB has been transferred. The Drive will reconnect when both the previous command and the RELEASE UNIT command has completed execution.
REQUEST SENSE
:= <initiator-part> <message-out> <command> <data-in> <completed>
The Drive will never disconnect when executing this command.
RESERVE UNIT
:= <initiator-part> <message-out> <command> <completed>.
This sequence will be used when the RESERVE UNIT command follows a non-Immediate type command.
:= <initiator-part> <message-out> <command> <disconnect>
<reconnect> <completed>
This sequence will be used when the RESERVE UNIT command follows an Immediate type command. The Drive will disconnect when the CDB has been transferred. The Drive will reconnect when both the previous command and the RESERVE UNIT command has completed execution.
REWIND
:= <initiator-part> <message-out> <command> <completed>.
This sequence will be used when the IMM bit is set and the REWIND command follows a non-Immediate type command other than a COPY, READ, VERIFY, SPACE, SEEK BLOCK, WRITE or WRITE FILE-MARKS command.
:= <initiator-part> <message-out> <command> <disconnect>
<reconnect> <completed>
This sequence will be uSed when the IMM bit is not set. The Drive will disconnect when the CDB has been transferred. The Drive will recon-nect when the tape is positioned at BOT(or when an error has been
de-tected). .
3-20 SCSl-2 Functional SpecifICations
<sequence 7>
<sequence 4>
<sequence 4>
<sequence 7>
This sequence will also be used when the REWIND command follows an Immediate type command. The Drive will disconnect when the CDB has been transferred. If the IMM bit is set, the Drive will reconnect when the previous Immediate type command bas completed execution. If the IMM bit is not set, the Drive will reconnect when both the previous Command and the REWIND command has completed execution.
This sequence will also be used when the IMM bit is set and the REWIND command follows a COPY, READ, VERIFY,SPACE, SEEK BLOCK, WRITE or WRITE FILEMARKS command. The Drive will dis-connect when the CDB bas been transferred. 'nle Drive will redis-connect as soon as the previous command bas terminated (read/space operation
This sequence will also be used when the IMM bit is set and the REWIND command follows a COPY, READ, VERIFY,SPACE, SEEK BLOCK, WRITE or WRITE FILEMARKS command. The Drive will dis-connect when the CDB bas been transferred. 'nle Drive will redis-connect as soon as the previous command bas terminated (read/space operation