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9.13
Streaming Feature Set
The Streaming feature set is an optional feature set that allows a host to request delivery of data from a contiguous
logical block address range within an allotted time. This places a priority on time to access the data rather than the
integrity of the data. Streaming feature set commands only support 48-bit addressing.
A device that implements the Streaming feature set shall implement the following minimum set of commands:
Configure Stream
Read Stream Ext
Write Stream Ext
Read Stream DMA Ext
Write Stream DMA Ext
Read Log Ext
Support of the Streaming feature set is indicated in Identify Device work 84 bit 4.
Note that PIO versions of these commands limit the transfer rate (16.6 MB/s), provide no CRC protection, and limit status
reporting as compared to a DMA implementation.
9.13.1
Streaming Commands
The streaming commands are defined to be time critical data transfers rather than the standard data integrity critical
commands. Each command shall be completed within the time specified in the Configure Stream command or in the
streaming command itself in order to ensure the stream requirements of the AV type application. The device may
execute background tasks as long as the Read Stream and Write Stream command execution time limits are still
met.
Using the Configure Stream command, the host may define the various stream properties including the default
Command Completion Time Limit (CCTL) to assist the device in setting up its caching for best performance. If the
host does not use a Configure Stream command, the device shall use the CCTL specified in each streami ng
command, and the time limit is effective for one time only. If the CCTL is not set by Configure Stream command, the
operation of a streaming command with a zero CCTL is device vendor specific. If Stream ID is not set by a Configure
Stream command, the device shall operate according to the Stream ID set by the streaming command. The
operation is device vendor specific.
The streaming commands may access any user LBA on a device. These commands may be interspersed with
non-streaming commands, but there may be an impact on performance due to the unknown time required to
complete the non-streaming commands.
The streaming commands should be issued using a specified minimum number of sectors transferred per command,
as specified in word 95 of the Identify Device response. The transfer length of a request should be a multiple of the
minimum number of sectors per transfer.
The host provided numeric stream identifier, Stream ID, may be used by the device to configure its resources to
support the streaming requirements of the AV content. One Stream ID may be configured for each read and write
operation with different command completion time limits be each Configure Stream command.
9.13.1.1
Urgent Bit
The Urgent bit in the Read Stream and Write Stream commands specifies that the command should be completed in
the minimum possible time by the device and shall be completed within the specified Command Completion Time
Limit.
9.13.1.2
Flush to Disk Bit
The Flush to Disk bit in the Write Stream command specifies that all data for the specified stream shall be flushed to
the media before posting command completion. If a host requests flushes at times other than the end of each
Western Digital Hard Disk Drive OEM Specification
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