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SCSI Commands

Quantum DLT 4000 Tape Drive 5-123

READ BUFFER Command (3Ch) (continued)

Table 5–58 READ BUFFER Command Descriptor Block - Field Descriptions

Field Name Description

Mode The tape drive supports the following values within this field. If any non-supported

value is set, the drive terminates the command with a CHECK CONDITION status,

ILLEGAL REQUEST sense key set.

Mode Description

000b Combined Header and Data (subsection 5.14.1)

010b Data (subsection 5.14.2)

011b Descriptor (subsection 5.14.3)

Buffer ID Must be 0, 1 or 2. If any other value appears in this field, the tape drive returns a

CHECK CONDITION status with ILLEGAL REQUEST sense key set.

Buffer Offset Not supported; must be 0. If any other value appears in this field, the tape drive

returns a CHECK CONDITION status with ILLEGAL REQUEST sense key set.

Allocation

Length

This field specifies the maximum number of bytes that the initiator has allocated

for returning data.

5.14.1 Combined Header and Data Mode

In this mode, the tape drive returns a 4-byte header followed by data bytes. The

drive terminates the DATA IN phase when the Allocation Length bytes of

header and data have been transferred or when all available data has been

transferred to the initiator, whichever is less. The 4-byte READ BUFFER header

is followed by data bytes from the target data buffer. The following figure

illustrates the format of the header.

Bit

Byte

7 6 5 4 3 2 1 0

0 Reserved

1 - 3

(MSB)

Available Length

(LSB)

Figure 5–60 READ BUFFER Header - Data Format

1 2 ... 218 219 220 221 222 223 224 225 226 227 228 ... 299 300

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