Emerson MVME147 manual Servicing the TARGET Requests

Servicing the TARGET Requests

c.Decode the link and flag bits and store the proper message to be presented during the message-in phase into the message-in buffer (pointed to by words $20 and $22 of the command table).

d.Create a TARGET sequence custom SCSI sequence packet as described in the TARGET Sequence Custom Sequence Packet section in Chapter 2. This packet should contain a pointer to the script described above and to the command table that was created or used. (You may wish to use the same command table that was provided for the TARGET enable call to the SCSI firmware.)

STEP 4: Call the SCSI firmware

Point address register A2 to the packet created in Step 3d above and jump into the SCSI firmware through the FUNNEL command entry.

After the proper service script and command table have been prepared by the user, a second custom SCSI sequence -- TARGET sequence packet must be issued to the firmware. This packet is intended to service the command that was just received. A script is passed to the firmware to be executed immediately following the reselection of the disconnected initiator. The firmware automatically performs the message-in phase with the identify message to reestablish the disconnected thread. This information transfer phase (message-in) should NOT be in the script.

The phases are performed as instructed by the script until a "$1C=FINISHED" is encountered. This is the signal for the firmware to either disconnect from the bus or to begin service of the next part of a linked command. The link information is passed to the firmware through the control byte of the CDB. If the link bit is set, the firmware makes the transition to the command phase, stores the received command and command count into the command table, makes the transition to the message-in phase, and issues a disconnect message followed by a SCSI bus disconnect. Some housekeeping later, the firmware returns to the user service routine with a final status of $xx19, stating that a command has been received following the completion of the earlier command serviced in a link. The service process then repeats.

If the serviced command has not been linked and a disconnect has been performed instead, the firmware cleans up some details and returns to the user service routine with a $xx18 final status.

A custom SCSI sequence -- TARGET sequence is shown in the TARGET Sequence Custom Packet section in Chapter 2.

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