Quantum 1200 Series DAT Autochanger Guia do Utilizador descarregar pdf (Página 228)

READ BUFFER Command (3Ch) SDLT 600 SCSI Interface Guide

4-186 January 2005 81-81200-02 REV A01

Compression

To reduce memory requirements for the diagnostic read buffers, and to reduce the size of the resulting

diagnostic information, the Live Buffer (A2h) can be compressed internally inside the drive before

being sent to the host. If you choose to do this, the process of generating the diagnostic information

takes longer, but the time to retrieve the information is reduced.

Using the compression feature is a good choice if you are retrieving the diagnostic information through

a slower interface—such as the ADT standard transport layer. The compression of the diagnostic read

buffer is enabled by setting bit 7 of byte 9 (the Control byte) in the mode 3 read buffer. A sample CDB

to do this is as follows:

3C 03 A2 00 00 00 00 00 04 80

4.17.2 Combined Header and Data Mode (00h)

In this mode, the 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.

Figure 4-96. READ BUFFER Header — Data Format

Bit

Byte

7 6 5 4 3 2 1 0

0 Reserved

1 - 3

(MSB)

Available Length

(LSB)

Table 4-108. READ BUFFER Header — Field Description

Field Name Description

Available Length Specifies the total number of data bytes available in the target’s buffer.

This number is neither reduced to reflect the allocation length nor to

reflect the actual number bytes written using the WRITE BUFFER

command. Following the READ BUFFER header, the drive transfers data

from its data buffer.

1 2 ... 223 224 225 226 227 228 229 230 231 232 233 ... 293 294

Sem comentários

Quantum 1200 Series DAT Autochanger Guia do Utilizador Página 228