Seagate SV35 SERIES ST3250824SV - Manual (Page 45)

SV35 Series SATA Product Manual, Rev. C 39
4.3.4 Streaming feature set support
The Streaming feature set is an optional feature set that allows a host to request delivery of data from a contig-
uous logical block address range within an allotted time. This places a higher priority on time to access the
data than the integrity of the data. Streaming feature set commands only support 48-bit, LBA-mode-only
addressing.
Seagate implements the following Streaming commands:
• CONFIGURE STREAM
• READ STREAM DMA EXT
• WRITE STREAM DMA EXT
Command Completion Time Out (CCTO) errors are not deferrable on DMA operations, as they require some
DMA engine clean up on the host side. Therefore, Seagate does not anticipate supporting any configurations
where a CCTO needs to hide from reporting as an error, and simply show up in a Stream Error log. Since the
Stream Error logs were intended to be used to report deferred errors such as this, Seagate has not imple-
mented them.
4.3.4.1 Identify Device command
These drives will set word 84 bit 4 (Streaming Feature Set Supported) and word 87 bit 4 (Configure Stream
command was issued) when a non-zero default time limit has been set for either reading or writing. If the host
reconfigures both defaults to 0, the bit will clear.
Word 95 (Stream Minimum Request Size)
World 95 contains the number of sectors that provide optimum performance in a streaming environment. This
number shall be a power of two, with a minimum of eight sectors (4096 bytes). The starting LBA value for each
streaming command should be evenly divisible by this request size.
Words 96, 97, and 104
Unsupported.
Words 99:98
These words define the fixed unit of time that is used only in the Command Completion Time Limit (CCTL) that
is passed in streaming commands. The unit of time for this parameter is microseconds. For example, a value of
50000 indicates 50 ms.
4.3.4.2 Streaming commands
Streaming commands are defined to be time-critical data transfers rather than the standard data-integrity-criti-
cal commands. Each command shall be completed within the time specified in the CONFIGURE STREAM
command or in the streaming command itself to ensure the stream requirements of the AV-type application.
The drive may execute background tasks as long as the READ STREAM and WRITE STREAM command exe-
cution time limits are still met.
The host may use the CONFIGURE STREAM command to define the default Command Completion Time
Limit (CCTL) for reads and writes independently--this assists the device in setting up its caching for best per-
formance. If the host does not use a CONFIGURE STREAM command, the device shall use the CCTL speci-
fied in each streaming command, and the time limit is effective for one time only. If the CCTL is not set by a
CONFIGURE STREAM command, the operation of a streaming command with a zero CCTL is device vendor
specific. "Stream ID" as noted in the ATA specification is not used by the Seagate implementation.