Chapter 8 Details of Usage
Target Mode Usage and SCSI Protocol Handling | Page 8 - 13 |
Wide Data
Transfer
Requests
When Wide Data Transfers are enabled, (WID bit set to 1, of the Unit Flags byte of either the Unit Options, 08H, or Extended Unit Options, 18H, commands), the adapter will send a Wide Data Transfer Request (WDTR) message whenever it determines that the data transfer agreement is in an indeterminate state. The adapter will initiate the exchange of WDTR messages immediately before starting the data transfer phase. The adapter will also send a WDTR message in response to a WDTR message received from the initiator.
Unexpected Messages Received from the Initiator
Automatic
Adapter
Responses
If an abort, bus device reset, or related message is received (during Target Mode command processing), it will be passed to the host as an unexpected event. The adapter will not disconnect from the SCSI bus until instructed to do so by the host. After receiving the message, the host issues the necessary adapter commands (Abort command) followed by a Target Mode Response command containing a Bus Free instruction to release the SCSI bus.
The adapter will automatically respond to several events without input from the host. These events are:
•
•A received
•A received Message Parity Error message
The adapter will retry the operation in progress whenever any of these events occur. The adapter will continue to retry the operation until the configured retry limit is exceeded (adapter Unit Options command).
Once the retry limit is reached, the adapter will attempt to send a status of Check Condition followed by a message of Command Complete. If a status byte has been sent, a Restore Pointers message is sent. This means that when the retry limit for a command is reached, the command can end in either of two ways:
•A status byte followed by a message
•A message followed by a status byte followed by a message
If the status/message cannot be sent without error, the adapter will go to the Bus Free phase (an unexpected disconnect). The Host will be notified of this occurrence and should prepare sense data for the initiator (Contingent Allegiance Condition).
The adapter will also automatically respond to the initiator’s data transfer negotiation requests:
•Synchronous Data Transfer Request (SDTR) message.
•Wide Data Transfer Request (WDTR) message.
User’s Guide | 21020285 D |
