Figure 3.38 Read Buffer Command: Echo Buffer Descriptor - Fujitsu MAX3073NC - SCSI,80, Dell DC961,Hard Drive Scsi Logical Interface Specifications

Command Specifications
The "Addressing boundary" field in the buffer descriptor indicates the addressing boundary in the data
buffer which can be specified in the WRITE BUFFER Command and the READ BUFFER Command as
a "Power" when expressed as a "Power of 2." The IDDs report X'02' (=2
to specify the address in 4-byte units. Also, the "Buffer capacity" field indicates the byte length of the
size of the data buffer which can be operated by the WRITE BUFFER and READ BUFFER commands.
Note: Exercise caution regarding the following points when using this command.
If the WRITE BUFFER command or READ BUFFER command is used under a multi-initiator or
multitask environment, it is necessary to be careful of the contents of the data buffer being changed
by another initiator or a command that issues another task during the interval between completion of
WRITE BUFFER command execution and execution of the READ BUFFER command.
(5) Mode = 1, 0, 1, 0 : Echo buffer
In this mode the IDD transfers data to the INIT from the echo buffer. The echo buffer shall transfer the
same data as when the WRITE BUFFER command with the mode field set to echo buffer was issued.
The BUFFER ID and BUFFER OFFSET fields are ignored in this mode.
(6) Mode = 1, 0, 1, 1 : Echo buffer descriptor
In this mode, a maximum of four bytes of READ BUFFER descriptor information is returned. The
device server shall return the descriptor information for the echo buffer. The "Buffer Offset" field is
reserved in this mode. The allocation length should be set to four or greater. The device server shall
transfer the lesser of the allocation length or four bytes of READ BUFFER descriptor. The READ
BUFFER descriptor is defined as shown in Figure 3.38.
Bit
Byte
0
1
2
3

Figure 3.38 READ BUFFER command: Echo buffer descriptor

The IDD return one in EBOS field, and the IDD verifies that echo buffer data from each initiator is the
same as that previously written by the same initiator.
The "Buffer Capacity" field returns the size of the echo buffer X'01FC' in bytes aligned to a four-byte
boundary.
3-118
7 6 5
Reserved
Echo Buffer Capacity (LSB)
2
), indicating that it is possible
4 3 2
Reserved
Reserved
Echo Butffer Capacity (MSB)
1 0
EBOS
C141-C010