Ciprico Rimfire 3880 manual Details of Usage Tagged Queuing Choose a tag message

Chapter 8 Details of Usage

Tagged Queuing Page 8 - 9

2. Choose a tag message.

There are three tag messages specified by the SCSI-2 and SCSI-3 protocol. You need only set the appropriate TAG OPTS bits in the Flags-2 field of the Pass- through Parameter Block for the command you are issuing to the SCSI device.

BITS

7	6	5	4	3	2	1	0
0	0	0	0	JSM	IAD	TAG OPTS

Table 113: Meaning of Flags-2 Field

These are the messages defined by the SCSI-2 and SCSI-3 specification, their meaning, and the TAG OPTS bit assignments for the Flags-2 field of the RF3880 command:

TAG OPT	Meaning
Value

SIMPLE QUEUE TAG MESSAGE: The command may be processed by the

00SCSI-2 or SCSI-3 device out of sequence for efficiency. Example: device may sort commands by logical block address.

ORDERED QUEUE TAG MESSAGE: The command must be executed by the

01SCSI-2 or SCSI-3 device in the order sent by the adapter (in order with respect to other commands sent with the Ordered Queue Tag Message.

HEAD OF QUEUE TAG MESSAGE: The command is executed by the SCSI-

102 or SCSI-3 device before all other commands previously sent, including other Head of Queue Tag commands but excluding the command currently in process.

Table 114: Meaning of TAG OPTS Bits

As you determine the types of tag messages you wish to use, you should be aware that there are rules of execution that your SCSI-2 or SCSI-3 device must follow for each tag message or combination of tag message commands. For example, determination of priority in the case of mixed tag messages, which executes first — an ORDERED QUEUE TAG or a SIMPLE QUEUE TAG? This situation and others are detailed in your SCSI-2 or SCSI-3 specification.

3. The RF3880 sends the tag message.

The RF3880 decodes these two bits, assigns a tag number and then manages the protocol for sending the proper message for the command.

How It Works This is how the RF3880 processes commands that use tag messages:

1.The tag message is sent after the identify message and before the SCSI command.

2.The adapter sends the commands in the exact order received from the host.

3.The queue tag number that is sent with the tag message is assigned by the adapter in ascending order beginning with 1, maximum of 255. When 255 is reached, the RF3880 starts over again with 1.

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