SCSI Commands: 31BREAD BUFFER
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A Mode of 00h requests that the data returned consists of a 4-byte descriptor header
followed by the data from the buffer. The 4-byte header is included in the number of
bytes specified by the Allocation Length. The Buffer ID and Buffer Offset fields are
reserved.
A Mode of 01h requests that data from the Medium Auxiliary Memory is returned.
A Mode of 02h requests that only the data from the buffer is returned.
A Mode of 03h requests that only the 4-byte descriptor header is returned. A Buffer
ID value for which there is no buffer associated will result in an all zero header. The
Buffer Offset field is reserved.
A Mode of 0Ah requests that the data from the echo buffer is returned.
A Mode of 0Bh requests that a maximum of four bytes of the descriptor information
for the echo buffer be returned.
The Buffer ID field indicates which buffer is to be read. All drives support buffer 0.
Other buffers may be available in the drive.
The Buffer Offset field may be used to specify the offset within the specified buffer
from which the data will be transferred.
The Allocation Length is used to specify the number of bytes that the initiator has
allocated for the returned data.
3.19.2
READ BUFFER Header
If the Mode field is set to 00h, then the data returned includes a 4 byte READ
BUFFER Descriptor. The following table shows the fields in the READ BUFFER
Descriptor.
Byte
Bits
7 6 5 4 3 2 1 0
0
Reserved (0)
1
(MSB)
2
3
Buffer Capacity
(LSB)
3.19.2.1
READ BUFFER Header Field Descriptions
Field
Bytes
Bits
Description
Reserved
0
All bits are 0.
Buffer Capacity
1-3
The capacity of the drive’s data buffer.
3.19.3
READ BUFFER Descriptor
If the Mode field is set to 03h, then the data returned is a 4 byte READ BUFFER
Descriptor. The following table shows the fields in the READ BUFFER Descriptor.
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