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SCSI Commands

Quantum DLT 8000 Tape System 5-167

READ BUFFER Command (3Ch) (continued)

5.16.1 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 figure below 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 5–75 READ BUFFER Header — Data Format

Table 5–75 READ BUFFER Header — Field Descriptions

Field Name Description

Available Length This field specifies the total number of data bytes available in the

target’s buffer. This number is not reduced to reflect the allocation

length, nor is it reduced to reflect the actual number bytes written

using the WRITE BUFFER command. Following the READ BUFFER

header, the target transfers data from its data buffer.

5.16.2 Data Mode

In this mode, the DATA IN phase contains only buffer data.

5.16.3 Descriptor Mode

In this mode, a maximum of four bytes of READ BUFFER descriptor information is

returned. The tape drive returns the descriptor information for the buffer specified by the

Buffer ID. In this mode, the drive does not reject the invalid Buffer IDs with a CHECK

CONDITION status, but returns all zeros in the READ BUFFER descriptor.

The Offset Boundary (Figure 5-76) is 12 (0Ch), indicating that buffer offsets should be

integral multiples of 4 K.

1 2 ... 306 307 308 309 310 311 312 313 314 315 316 ... 407 408

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Quantum DLT 8000 Manual Página 311