Seagate Medalist ST31082A, Руководство по эксплуатации продукта

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Command Set Chapter 7
Technical Reference Manual Page 75
A Write Long may be executed by setting the long bit in the command code.
The Write Long command writes the data and the ECC bytes directly from the
sector buffer; the drive will not generate the ECC bytes itself for the Write
Long command. Data byte transfers are 16-bit transfers and ECC bytes are 8-
bit transfers.
Write Caching
Write caching is activated by clearing the Feature Word bit 2. Once write
caching is active, the Write Sector(s) command is cached. This command is
then referred to as a “cached write.”
When a cached write command is received, the data is taken from the host and
ending status is posted before the data has been written to the disk.
• If the next command is a cached write and the data is logically sequential,
the data is taken from the host immediately.
• If the next command is a cached write that is not logically sequential, the
drive will wait for the previous write to finish before taking data from the
new write. Read commands work similarly; the previous write is allowed to
finish before the read operation starts.
In addition to caching, dynamic sparing of bad sectors has been implemented
for cached write commands. This ensures that cached data that has already
been reported as written successfully gets written, even if an error should
occur.
If a sector cannot be written, the drive will dynamically assign an alternate
sector and continue writing the data. If an error occurs during re-allocation, the
drive will drop out of write caching and report the error as an ID Not Found. If
the write command is still active on the AT interface, the error is reported
during that command; otherwise, it is reported on the next command.
Write Sector Buffer
Command Number: E8 hex
Description: The Write Buffer command allows the host to overwrite the
contents of the drive’s sector buffer with any data pattern desired. Only the
Command register is valid for this command.
When this command is issued, the drive will set BSY, set up the sector buffer
for a write operation, set DRQ, reset BSY. The host may then write up to 512
bytes of data to the buffer.