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TARGET Sequence Custom Packet
2-25
2
WORDS $04 and $06:
SCRIPT POINTER -- The address of the TARGET script to be
performed to service the initiator request.
In TARGET role, the MVME147 controls the SCSI bus. The
TARGET script tells the firmware which information transfer
phases to cycle through to service the initiator request that
was encoded in the CDB.
Note
In TARGET role, the names of the information transfer
phases are consistent with initiator role. By SCSI
definition, transfer direction is always referenced to the
initiator. That is, the message in phase is a message transfer
INTO the initiator. For TARGET role the message-in phase
is still INTO the initiator (notice it is OUT of the TARGET).
TARGET scripts to service commands do not include
command phases. Below are examples of TARGET scripts for
two CDBs; one is a receive CDB and the other is a send CDB.
Example 1: Receive (peripheral device type = processor
devices)
CDB byte 0: $08 Command is a receive
CDB byte 1: $20 The desired LUN is 1
CDB byte 2: $00 Allocation length MSB
CDB byte 3: $04 Allocation length
CDB byte 4: $00 Allocation length LSB
CDB byte 5: $00 Control byte=0: no link, no flag
Target script for example 1:
DC.B $0C DATA-IN PHASE
DC.B $10 STATUS PHASE
DC.B $18 MESSAGE-IN PHASE
DC.B $1C END OF TARGET SCRIPT
The command table contains the information required to
carry out the bus phase. For example, the data pointer tells
the firmware where the buffers are located in MVME147-
accessible memory.
1. During the data-in phase, the $400 bytes are sent to the initiator.
2. During the status phase, the GOOD status is sent to the initiator.