Fujitsu MHW2040AC User Manual Page 253
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6.4 Read-ahead Cache
6.4.2 Caching operation
The caching operation is performed only when the commands listed below are
received. If any of the following data are stored on the data buffer, the data is sent
to the host system.
• All of the sector data that this command processes.
• A part of the sector data including the start sector, that this command
processes.
If part of the data to be processed is stored on the data buffer, the remaining data is
read from disk media and sent to the host system.
(1) Commands that are targets of caching
The commands that are targets of caching are as follows:
• READ SECTOR(s)
• READ MULTIPLE
• READ DMA
• READ SECTOR(s) EXT
• READ DMA EXT
• READ MULTIPLE EXT
However, if the caching function is prohibited by the SET FEATURES command,
the caching operation is not performed.
(2) Data that is a target of caching
The data that is a target of caching are as follows:
1) Read-ahead data that is read from disk media and saved to the data buffer
upon completion of execution of a command that is a target of caching.
2) Pre-read data that is read from disk media and saved to the data buffer before
execution of a command that is a target of caching.
3) Data required by a command that is a target of caching and has been sent to
the host system one. If the sector data requested by the host has not been
completely stored in the read cache portion of the buffer, this data does not
become a target of caching. Also, if sequential hits occur continuously, the
caching-target data required by the host becomes invalid because that data is
overwritten by new data.
(3) Invalidating caching-target data
Data that is a target of caching on the data buffer is invalidated under the
following conditions:
C141-E258 6-13
- MHW2060AC, MHW2040AC 1
- DISK DRIVES 1
- PRODUCT MANUAL 1
- FOR SAFE OPERATION 2
- Revision History 3
- Preface 5
- Operating Environment 6
- Conventions 6
- Attention 7
- Liability Exception 7
- Important Alert Items 9
- Manual Organization 11
- Contents 13
- Illustrations 19
- CHAPTER 1 Device Overview 23
- 1.1 Features 24
- 1.1.3 Interface 25
- 1.2 Device Specifications 26
- 1.3 Power Requirements 29
- 1.5 Acoustic Noise 33
- 1.6 Shock and Vibration 33
- 1.7 Reliability 34
- 1.8 Error Rate 35
- 1.9 Media Defects 35
- 1.10 Load/Unload Function 35
- 2.1 Device Configuration 40
- 2.2 System Configuration 41
- 2.2.3 2 drives connection 42
- 3.1 Dimensions 44
- 3.2 Mounting 45
- Connector 50
- 3.3.3 Device connection 51
- 3.4 Jumper Settings 52
- 3.4.4 CSEL setting 54
- 4.1 Outline 58
- 4.2 Subassemblies 58
- 4.3 Circuit Configuration 59
- C141-E258 4-5 61
- 4.4 Power-on Sequence 62
- 4.5 Self-calibration 63
- 4.6 Read/write Circuit 65
- 4.6.3 Read circuit 66
- 4.6.4 Digital PLL circuit 67
- 4.7 Servo Control 68
- Theory of Device Operation 72
- 4-16 C141-E258 72
- 4.7.3 Servo frame format 73
- 4.7.5 Spindle motor control 75
- CHAPTER 5 Interface 77
- 5.1 Physical Interface 78
- 5.2 Logical Interface 82
- 5.2.1 I/O registers 83
- 5.3 Host Commands 90
- 5.3.2 Command descriptions 94
- • Default function 110
- • Unload Feature: 110
- • Attribute ID 123
- • Raw attribute value 124
- • Status Flag 124
- • Current attribute value 124
- • Error logging capability 127
- • Check sum 127
- • SMART error logging 128
- • Command data structure 130
- • Error data structure 130
- • Status 130
- • SMART self-test 131
- • Self-test number 131
- • Self-test index 131
- • Test span 132
- • Current LBA under test 132
- • Current span under test 132
- • Feature Flags 133
- (CM) 1 1 1 0 0 1 0 0 149
- • SET MAX ADDRESS 180
- Password information 182
- • SET MAX SET PASSWORD 184
- • SET MAX LOCK 184
- • SET MAX UNLOCK 184
- • Description 186
- 5.3.3 Error posting 203
- Interface 204
- 5-128 C141-E258 204
- 5.4 Command Protocol 205
- (*) Transfers dummy data 207
- 5.4.4 Other commands 211
- 5.5 Ultra DMA Feature Set 213
- 5.5.2 Phases of operation 214
- 5.5.5 Ultra DMA CRC rules 223
- 5.6 Timing 225
- 5.6.4 Power-on and reset 240
- CHAPTER 6 Operations 241
- 6.1.1 Response to power-on 242
- 6.2 Power Save 247
- 6.3 Defect Processing 249
- Sector (physical) 250
- Cylinder 0 250
- (Not used) 250
- 779 780 251
- 6.4 Read-ahead Cache 252
- For MPU work For R/W command 252
- 8,388,608 bytes 252
- 6.4.2 Caching operation 253
- 256
- 6.5 Write Cache 258
- Glossary 261
- Acronyms and Abbreviations 265
- Comment Form 273
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