SpinPoint Barracuda Series, Product Manual

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Barracuda Product Manual Rev04
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5.2.2.3 The Disk ECC Control Block
The Disk Control block supports a programmable Reed-Solomon ECC. The code is capable of correcting up
to 36 bytes , or if correcting with erasure pointer up to 72 bytes. Error detection and correction is handled in
the Disk Control block. Automatic on-the-fly hardware correction will take place for up to 32 bytes.
Correction is guaranteed to complete before the ECC Field of the sector following the sector where the error
occurred utilizing standard ATA sector size. An added feature of the Barracuda ECC block is the ability to
log corrected ECC errors for error reporting. To add the data correction capability a 10-bit permuted ECC
that supports high rate RLL is implemented. The user data is first encoded before the ECC is added. This will
allow the ECC correction be more effectively working on the data directly coming from the media.
5.2.2.4 Power Management
Power management features are incorporated into each functional block of the Barracuda. This allows the
host to control the amount of power of the specific power save states. Other power management features
include:
 Independent power management control for each block.
 DSP block can be powered down and up when needed.
 Disk Sequencer and associated disk logic powered up when the Disk Sequencer is started.
 Weak pull-up structure on input pins to prevent undesirable power consumption due to floating CMOS
inputs.
5.2.3 Read/Write Circuit
The Read/Write Channel control circuit provides read/write-processing functions for the drive. The
Read/Write circuit receives the RD GATE and WR GATE signals, write data, and servo AGC and gates from
the Disk Format Sequencer. The Read/Write Channel sends decoded read data and the read reference clock to
the Disk Format Sequencer.
The Barracuda has an embedded Read Channel designed in the SOC. The Read Channel is a sampled-data
digital PRML channel designed to work with the Disk Controller and read/write Preamplifier to provide the
signal processing elements required to build a state of the art high density, high speed disk drive. The Read
Channel block implements a Trellis-coded noise predictive PRML read channel (supporting) zone-bit
recording which stores more bits on the outer disk radius.
5.3 Servo System
The Servo System controls the precise position of the read/write heads to keep them on “track”. The Servo
System also compensates for write/read head offsets and thermal drifts, disk fluttering and run-out ( i.e. track
mis-registration or TMR), and external vibration. The Barracuda has an Embedded Sector Servo System.
Positioning information is radially located in evenly spaced servo sectors on each track.
Radial position information can be provided from these sectors for each data head. Because the drive
incorporates multiple data zones and each zone has a different bit density, split data fields are necessary for
optimal use of the non-servo area of the disk. The servo area remains phase-coherent across the surface of
the disk, even though the disk has various data zones. The main advantage of the Embedded Sector Servo
System is that it eliminates the problems of static and dynamic offsets between heads on different surfaces.