Fujitsu M2488, Руководство по эксплуатации продукта

Страница: 131 / 528

M2488 PRODUCT GUIDE TAPE UNIT SCSI COMMANDS
April 1997 CG00000-011503 REV. A 4-49
4-3.11 LOOP WRITE TO READ command C1h
The LOOP WRITE TO READ (LWR) command transfers one block of data from the initiator and
performs an internal LWR operation. This command is used to check the controller’s data and control
path; the data path checked includes the analog circuitry. After the receipt of a valid LWR command,
tape synchronization is performed prior to execution of the LOOP WRITE TO READ operation.
4-3.11.1 LOOP WRITE TO READ CDB Description
LOOP WRITE TO READ is a ten-byte command. The bytes are shown below and described in
Table 4-41. Common fields are described in paragraph 4-3.1 on page 4-4.
BITS
BYTES 7 6 5 4 3 2 1 0
0 1 1 0 0 0 0 0 1
1 LUN Reserved Fixed
2 MSB
Transfer Length 3
4
LSB
5 Reserved
6 Reserved
7 Reserved
8 Reserved
9 Reserved Flag Link
Note: Changeable fields in the CDB are shaded.
Table 4-41. LOOP WRITE TO READ Field Description
BYTE BIT VALUE DESCRIPTION
0 0-7 C1h Operation code.
1 0
0
1
The Fixed bit specifies both the meaning of the transfer length field and whether
fixed-length or variable-length block(s) are to be transferred.
If the Fixed bit is zero, a single block is transferred from the initiator and looped
through the controller.
If the Fixed bit is set to one, the transfer length field specifies the number of block(s)
to be transferred from the initiator. This form of the LWR command is valid only if
the logical unit is currently operating in fixed block mode (i.e., it has been instructed
to use fixed-length blocks by a MODE SELECT command). Only a block count of 0
or 1 may be specified.
2-4 The Transfer Length specifies the length of the block to be transferred from the ini-
tiator.
If the transfer length specified by the LWR command is 0, no data is transferred and
this condition is not considered an error.