Quantum ATL SuperLoader ATL, User Manual

Page: 139 / 196

Chapter 3 Media Changer Commands
Read Buffer Command (3Ch)
Quantum ATL SuperLoader Software Interface Guide 121
Table 51 Read Buffer
Command Descriptor
Block
The host should first send a READ BUFFER command, in
Descriptor mode, to determine the size of the buffer being
returned. In response to the READ BUFFER command, the device
returns four bytes of data, three of which contain the size of the
buffer. The host can then use this data to establish the Buffer
Offset/Allocation Length fields of the CDB. Once the size of the
buffer is known, Mode 2 (Data Only, see Data Mode (0010b) on
page 123) can be used to transfer the data across the SCSI Bus.
Field Name Description
Mode The SuperLoader 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
0000b Combined Header and Data Mode (000b) on page 122 (LTO
only)
0010b Data Mode (0010b) on page 123 (LTO only)
0011b Descriptor Mode (0011b) on page 123 (LTO only)
1010b Read Data from Echo Buffer (1010b) on page 123
1011b Echo Buffer Descriptor Mode (1011b) on page 124
Buffer ID This field is ignored in some modes and reserved in others. Refer to the
specific mode description for more detail.
Buffer Offset This field is ignored in some modes, reserved in others, and valid in mode
0010b. Refer to the specific mode description for more detail.
Allocation Length This field specifies the maximum number of bytes that the initiator has
allocated for returning data. The host uses this field to limit the size of
data transfers to its own internal buffer size.