User's Guide

62 SCSI Commands
Read Buffer – 3Ch
What the Library Does With This Command
The library will return requested buffer descriptor information or buffer data.
Command Usage
This command can be used primarily for enhanced domain validation. The initiator can use Descriptor mode
first to determine the size of the data available to read, followed by Data mode to then read it. Depending
on the size of the requested buffer, it can also be retrieved in blocks, utilizing offsets into the buffer.
Read Buffer CDB Format
The READ BUFFER CDB format is shown in the following table.
Mode – The supported modes are:
• 2h – Data
• 3h – Descriptor
• Ah – Echo Buffer
• Bh – Echo Buffer Descriptor
In Data Mode, data is transferred from the buffer specified by the Buffer ID field. Buffer IDs are assigned
beginning with zero, and are assigned contiguously. Buffer ID code assignments for the READ BUFFER
command are the same as for the WRITE BUFFER command.
In Descriptor Mode, a maximum of four bytes of READ BUFFER descriptor information is returned. The
library returns the descriptor information for the buffer specified by the buffer ID. If there is no buffer
associated with the specified Buffer ID, all zeros are returned in the READ BUFFER descriptor. The Buffer
Offset field is reserved in this mode. The allocation length should be set to at least four for this mode. See
Table 60
on page 63 for a definition of the READ BUFFER descriptor.
Table 59 READ BUFFER CDB format
Bit
Byte
76543210
0 Op Code (3Ch)
1 Logical Unit Number Rsvd Mode
2 Buffer ID
3
:
5
Buffer Offset
6
:
8
Allocation Length
9 Control