Read Buffer - IBM Ultrium Internal Tape Drive T200 Reference Manual

READ BUFFER

The READ BUFFER command reads data from the memory on the drive and sends
it to the initiator.
Modes 000b, 010b and 011b are supported. If it is set to 010b, then just the data is
returned. If it is set to 011b, just the descriptor is returned.
If the Mode is set to 0111b and the Buffer ID is 0, the descriptor returned is for the
Main Data buffer. The format of the 4-byte descriptor is shown in Table 64. The
Buffer ID indicates which buffer is to be read. The Buffer Offset field may be set to
any address in the buffer.
Note: The Main Data buffer is larger than capacity of the read buffer offset and
Table 63. READ BUFFER Command
7 6
0
1 Logical Unit Number (0)
2
3
:
5
6
:
8
9
capacity fields to express (32 megabytes). To compensate for this, the buffer
offset and capacity fields for the Main Buffer (buffer ID = 0) are interpreted
and expressed such that each unit represents 64 bytes. This is only true for
buffer modes 000b, 001b, 010b, 011b, and 111b.
Table 64. READ BUFFER Descriptor
7 6
0
1
:
3
5 4 3
Operation Code (3Ch)
Reserved
Buffer ID
Buffer Offset
Allocation Length
Control
5 4 3
Reserved
Buffer Capacity
Chapter 2. Command Support
2 1 0
Mode
2 1 0
49