TAPE UNIT SCSI COMMANDS

M2488 PRODUCT GUIDE

4-3.14.2 READ CHECK CONDITION Status

The following table describes how a CHECK CONDITION occurs.

FIXED

SILI

BLOCK

DESCRIPTION

BIT

BIT

MODE *

 

 

 

 

 

1

1

 

Causes CHECK CONDITION status with the sense key being ILLEGAL REQUEST.

 

 

 

 

0

1

variable

No CHECK CONDITION is set due to an actual block length being different than the

 

 

 

length specified in the Transfer Length field, except for the following condition.

 

 

 

The target still reports CHECK CONDITION status for an incorrect length condi-

 

 

 

tion if the overlength condition exists and the block length field in the mode param-

 

 

 

eter block descriptor is non-zero (a non-zero value in this field in the Mode Select

 

 

 

data implies fixed mode). The overlength condition exits after executing a Read

 

 

 

command when the length of the actual block read exceeds the requested transfer

 

 

 

length in the CDB.

 

 

 

 

0

0

variable

With Fixed bit = 0, the transfer will take place in variable block mode independent of

 

 

 

the value in the mode parameters block descriptor. In variable block mode, a single

 

 

 

block is transferred with the bytes transferred being the lesser of the actual block

 

 

 

length or the requested Transfer Length.

 

 

 

A successful READ command with the fixed bit of zero, transfers the requested trans-

 

 

 

fer length in bytes to the initiator.

 

 

 

If the actual block length is different from the specified transfer length, CHECK

 

 

 

CONDITION status is returned to the initiator. The incorrect length indicator (ILI)

 

 

 

bit and valid bit in the sense data are set to one, and the sense key is set to NO

 

 

 

SENSE. The information bytes contained in the sense data are set to the difference

 

 

 

(residue) of the requested transfer length minus the actual block length, and this value

 

 

 

will be negative (two’s compliment) when the actual block length exceeds the

 

 

 

requested block length. Upon termination, the logical position is located after the

 

 

 

incorrect length block (EOM side).

 

 

 

 

1

 

fixed

The transfer length specifies the number of blocks to be transferred to the initiator.

 

 

 

This form of the READ command is valid only if the logical unit is currently operat-

 

 

 

ing in fixed block mode. A logical unit is in fixed block mode if it has been instructed

 

 

 

by the MODE SELECT command to use fixed-length blocks. In this case, the current

 

 

 

block length is the block length defined in the MODE SELECT command.

 

 

 

A successful READ command with the fixed bit of one, transfers the requested trans-

 

 

 

fer length times the current block length in bytes to the initiator.

 

 

 

If the actual block length read is different from the current transfer length, as speci-

 

 

 

fied in the mode parameters block descriptor, CHECK CONDITION status is gener-

 

 

 

ated. The ILI bit and valid bit are both set to one, and the sense key is set to NO

 

 

 

SENSE. The information bytes in the sense data are set to the difference of the

 

 

 

requested transfer length minus the actual number of blocks read (not including the

 

 

 

incorrect length block). Upon termination, the logical position is located after the

 

 

 

incorrect length block (EOM side).

 

 

 

 

1

 

variable

The target rejects the command by returning CHECK CONDITION status and by set-

 

 

 

ting the sense key to ILLEGAL REQUEST.

 

 

 

 

4-64

CG00000-011503 REV. A

April 1997

Page 145 Page 147
Page 146
Image 146
Fujitsu M2488 manual Read Check Condition Status, Fixed Sili Block Description BIT Mode
Page 145 Page 147
Top Page Image Contents