Seagate Technology 10002475-003, Руководство по описанию продукции

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ATAPI Interface Chapter 5
Product Description Manual Page 49
Read Position
Bit
Byte
7 6 5 4 3 2 1 0
0 Operation code (34h)
1 Reserved
2 Reserved
3 Reserved
4 Reserved
5 Reserved
6 Reserved
7 Reserved
8 Reserved
9 Reserved
The following table describes the Read Position layout.
Byte Description Value Meaning
0 BOP, EOP, BPU nn 80h = Beginning of Partition
40h = End of Partition
04h = Block Position Unknown
1 Partition Number 00/01h Current Partition (bit 0)
2,3 Reserved 00h -
4-8 First Block Location
(Host Block Location) NNNNNNNN Logical Number of next block to transfer
between host and buffer
8-11 Last Block Location
(Medium Block
Location) NNNNNNNN* Not Supported
12 Reserved 00h —
13-15 Blocks in Buffer 000000* Not Supported
16-19 Bytes in Buffer 00000000* Not Supported
*These fields might appear to report the number of bytes/blocks in the buffer.
However, this information is not guaranteed to be accurate. You should not rely
on this information.
The only position that is guaranteed is the host logical block position. The First
and Last Block Locations both return the same host location, and Blocks and
Bytes in Buffer are reported as 0.
Because Read Position is DSC restrictive on all ATAPI tape drives, it can be
used to “wait” for any previous command to complete. This can be useful for
applications with ATAPI only access to determine the actual completion of a
command. Note, this will keep the ATA bus busy during the “wait”. DSC polling
(to wait for DSC set) is preferred when possible.