Barracuda Product Manual Rev04
38
The Barracuda Servo System is classified as a digital servo system because track-following and seek control,
bias cancellation, and other typical tasks are done in a Digital Signal Processor (DSP).
The Servo system has three modes of operation: track-following mode, settle mode, and trajectory based
control mode.
1.
Track-following mode is used when heads are “on-track.” This is a position loop with an
integrator in the compensation.
2.
Settle mode is used for all accesses; head switches, short-track seeks and long-track seeks.
Settle mode is a position loop with velocity damping. Settle mode does not use feed forward.
3.
Trajectory based control mode is used for acceleration and deceleration of the actuator for seeks
of one or more tracks. A seek operation of this length is accomplished with a combination of
position & velocity control loop as well as acceleration feed-forward. The trajectories are
calculated by DSP using a pre-determined seek time according to the seek length.
5.4 Read and Write Operations
The following two sections describe the read and write data path.
5.4.1 The Read Path
The drive has one read/write head for each of the data surfaces. The signal flow for the read path starts at the
read/write heads. When the magnetic flux transitions recorded on a disk pass under the head, they generate
low-amplitude, differential voltages. The read/write head transfers these signals to the flexible circuit’s
amplifier, which amplifies the signal.
The flexible circuit transmits the pre-amplified signal from the HDA to the PCBA. The EPRML channel on
the PCBA shapes, filters, detects, synchronizes, and decodes the data from the disk. The channel then sends
the resynchronized data output to the Disk Format Sequencer.
The Disk Controller manages the flow of data between the Disk Format Sequencer and SATA Host Interface
Block. It also controls data access for the external DRAM buffer. The Disk Sequencer module identifies the
data as belonging to the target sector. After a full sector is read, the Disk Format Sequencer checks to see if
it needs to apply an ECC correction to the data. The Buffer Controller manages the location of data to be
stored in the DRAM buffer. Once the data buffer is full, the Buffer Manager sends signal to stop further data
transfer.
The SATA Host Interface Block retrieves data from the DRAM buffer to the host. In response to a host
request, the Host Interface Controller delivers data based on the transfer mode that host requested, such as
PIO, DMA, or FPDMA. The DSP along with the intelligent controller firmware will manage the caching
algorithm of the drive.
5.4.2 The Write Path
The signal path for the write path follows the reverse order of that for the read path. The host transmits data
via the SATA bus to the SATA Interface Control block. The Buffer Controller section stores the data in the
buffer and stops the data transfer if buffer is full. Because the data is transmitted to the drive at a rate that is
different from the rate the drive can write data to the disk media, data is stored temporarily in the DRAM
Summary of Contents for Barracuda Series
Page 1: ...Barracuda Series Product Manual 3 5 Hard Disk Drives January 11 2012 Rev5...
Page 19: ...SPECIFICATIONS Barracuda Product Manual Rev04 14 1D...
Page 23: ...Barracuda Product Manual Rev04 18 2D Figure 4 1 Mechanical Dimension...
Page 25: ...Barracuda Product Manual Rev04 20 1D...
Page 26: ...Barracuda Product Manual Rev04 21 2D Figure 4 2 Mounting Dimensions...
Page 36: ...Barracuda Product Manual Rev04 31 1D...
Page 37: ...Barracuda Product Manual Rev04 32 2D Figure 5 1 Exploded View of Barracuda HDD...