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Spinpoint
M8 Product Manual REV
2.3
33
The Sequencer module identifies the data as belonging to the target sector. After a full sector is read, the
88i9322 (Rev2.0) checks to see if the firmware needs to apply an ECC algorithm to the data. The Buffer Control
section of the 88i9322 (Rev2.0) stores the data in the cache and transmits the data to the AT bus.
5.4.2 The Write Channel
The signal path for the Write Channel follows the reverse order of that for the Read Channel. The host transmits data
via the AT bus to the 88i9322 (Rev2.0) Interface Controller. The Buffer Controller section of the 88i9322 (Rev2.0)
stores the data in the cache. Because the data is transmitted to the drive at a rate that exceeds the rate at which the
drive can write data to the disk, data is stored temporarily in the cache. Thus, the host can present data to the drive at
a rate independent of the rate at which the drive can write data to the disk.
Upon correct identification of the target address, the data is shifted to the Sequencer, which generates and appends
an error correcting code. The Sequencer then converts the bytes of data to a serial bit stream. The AT controller also
generates a preamble field, inserts an address mark, and transmits the data to the ENDEC in the R/W IC where the
data is encoded into the LDPC format and pre-compensates for non-linear transition shift. The amount of write
current is set by the 88i9322 (Rev2.0) DSP and Interface/Disk Controller through the serial interface to the
preamplifier.
The 88i9322 (Rev2.0) switches the Preamplifier and Write Driver IC to write mode and selects a head. Once the
Preamplifier and Write Driver IC receives a write gate signal, it transmits current reversals to the head, which writes
magnetic transitions on the disk.
5.5 Firmware Features
This section describes the following firmware features:
Read Caching
Write Caching
Track Skewing
Defect Management
Automatic Defect Allocation
ECC Correction
SMART (Self-monitoring and reporting technology)
ATA security mode features
ATA host protected area
ATA streaming features
ATA power up in stand by feature set
ATA advanced power management (APM) feature set
ATA device configuration overlay (DCO) feature set
5.5.1 Read Caching
The Spinpoint M8 hard disk drive uses Read Cache to enhance drive performance and significantly improve system
throughput. Use the SET FEATURES command to enable or disable Read Caching. Read caching anticipates
host-system requests for data and stores that data for faster future access. When the host requests a certain segment
of data, the cache feature utilizes a prefetch strategy to get the data in advance and automatically read and store the
following data from the disk into fast RAM. If the host requests this data, the RAM is accessed rather than the disk.