SCSI Commands: 31BREAD BUFFER
Page
141
3.19
READ BUFFER
The READ BUFFER command reads data from the memory on the drive and sends
it to the initiator. This command is used in conjunction with the WRITE BUFFER
command as a diagnostic function for testing the drive buffer memory and
confirming the SCSI bus or Fibre Channel interface integrity. The tape is not
accessed during execution of this command.
3.19.1
READ BUFFER Command Descriptor Block
Byte
Bits
7 6 5 4 3 2 1 0
0
Operation Code (3Ch)
1
Ignored LUN
Mode
2
Buffer ID
3
(MSB)
4
5
Buffer Offset
(LSB)
6
(MSB)
7
8
Allocation Length
(LSB)
9
Control
3.19.1.1
READ BUFFER Command Field Descriptions
Field
Bytes
Bits
Description
Operation
Code
0
The operation code for READ BUFFER is 3Ch.
Ignored
Logical Unit
1
5-7
The LUN field is vestigial from the SCSI-1 standard and is ignored.
Mode
1
0-4
00h = Return descriptor and data.
01h = Return Medium Auxiliary Memory (MAM), EEPROM or
FLASH data.
02h = Return data only.
03h = Return descriptor only.
04h = Return trace buffer data.
0Ah = Return echo buffer.
0Bh = Return echo buffer descriptor.
Buffer ID
2
00h = normal access (default)54h = specifies access to MAM
Buffer Offset
3-5
For Mode not equal 01h: The offset from the beginning of the
specified buffer in bytes.
For Mode equal 01h: Set to the MAM page code as described in
the tables or FFFFFFh to specify the entire MAM.
Note: Buffer Offset for FCP and SAS interface drives must have a
Mod 4 = 0 characteristic. I.e. must be evenly divisible by 4.
Allocation
Length
6-8 Specifies the amount of data bytes to be returned. A value of 0 is a
valid entry and returns no data.
The drive stops sending data when the number of bytes specified
has been transferred or when all available data has been sent.
Reserved
All reserved bits must be 0.
Control 9
See
SCSI Command Control Byte Format on page 25.
Summary of Contents for LTO 4
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