Reference Guide

Chapter 4 SCSI Commands
READ BUFFER Command (3Ch)
DLT-S4 Interface Reference Guide 265
Table 148 READ BUFFER
Command Descriptor Block
—
Field Descriptions
Field Description
Mode The drive supports the following values for this field.
Mode Description
00h Combined Header and Data Mode (see page 266)
02h Data Mode (see page 266
)
03h Descriptor Mode (see page 267
)
0Ah Read Data from Echo Buffer (see page 267
)
0Bh Echo Buffer Descriptor Mode (see page 268
)
Buffer ID Indicates from which buffer the data is to be transferred. Possible values are:
Buffer Description
00h This 32 KB buffer is used with the WRITE BUFFER command to provide a
diagnostic capability for testing the SCSI bus or Fibre Channel or SAS
network, hardware integrity, or both.
01h This buffer is used to read the drive’s RAM and EEPROM. Its effective size is
8186 KB.
02h This buffer is used to read the drive’s data cache RAM. The Available Length
field returned in Combined Header and Data mode and the Buffer Capacity
field returned in Descriptor mode are not large enough to express the size of
the data cache RAM, so both fields return to 0.
03h This buffer is used to read the DMARK table.
A1h This buffer provides access to diagnostic information saved from an earlier
event. (Saved Buffer.)
A2h This buffer provides real-time access to diagnostic information. (Live Buffer.)
Note: In Data mode or Combined Header and Data mode, any other value besides those listed is
illegal. In Descriptor mode, any other value returns all zeros in the descriptor. In Read Data
from Echo Buffer and Echo Buffer Descriptor modes, this field is ignored.
Buffer Offset Allows the host to specify the location of the start of the data within the buffer. This field
is reserved and must be set to 0 for all modes except Data modes.
Allocation
Length
Specifies the maximum number of bytes 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.