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Chapter 9

Memory Protection Unit

This chapter describes the processor Memory Protection Unit (MPU). It contains the

following sections:

• About the MPU on page 9-2

• MPU programmer’s model on page 9-3

• Interrupts and updating the MPU on page 9-19

• MPU access permissions on page 9-13

• MPU aborts on page 9-15

• Updating an MPU region on page 9-16.

Main Page

Default Chapter5
- Table of Contents5
Preface20
- About this Book20
- Key to Timing Diagram Conventions23
- Feedback25
Chapter 1 Introduction28
- About the Processor28
- Components, Hierarchy, and Implementation30
- Figure 1-1 Cortex-M3 Block Diagram31
- Table37
- Execution Pipeline Stages38
- Figure 1-2 Cortex-M3 Pipeline Stages38
- Prefetch Unit40
- Branch Target Forwarding41
- Store Buffers44
- Product Revisions45
- About the DP46
Chapter 2 Programmer's Model50
- About the Programmer's Model50
- Privileged Access and User Access51
- Registers52
- Figure 2-1 Processor Register Set52
- Table 2-1 Application Program Status Register Bit Assignments54
- Figure 2-2 Application Program Status Register Bit Assignments54
- Figure 2-3 Interrupt Program Status Register Bit Assignments54
- Table 2-2 Interrupt Program Status Register Bit Assignments55
- Table 2-3 Bit Functions of the EPSR56
- Figure 2-4 Execution Program Status Register56
- Data Types58
- Memory Formats59
- Figure 2-5 Little-Endian and Big-Endian Memory Formats60
- Instruction Set Summary61
- Table 2-4 16-Bit Cortex-M3 Instruction Summary61
- Table 2-5 32-Bit Cortex-M3 Instruction Summary64
Chapter 3 System Control73
- Copyright © 2005-2008 ARM Limited. All Rights Reserved73
- Summary of Processor Registers74
- Table 3-1 NVIC Registers74
- Table 3-2 Core Debug Registers74
- Core Debug Registers77
- Table 3-3 Flash Patch Register Summary78
- Table 3-4 DWT Register Summary79
- Table 3-5 ITM Register Summary81
- Table 3-6 AHB-AP Register Summary82
- Table 3-7 Summary of Debug Interface Port Registers82
- Table 3-8 MPU Registers83
- Table 3-9 TPIU Registers84
- Table 3-10 ETM Registers85
Chapter 4 Memory Map89
- About the Memory Map90
- Figure 4-1 Processor Memory Map90
- Table 4-1 Memory Interfaces91
- Table 4-2 Memory Region Permissions92
- Bit-Banding93
- Figure 4-2 Bit-Band Mapping94
- ROM Memory Table95
- Table 4-3 ROM Table95
Chapter 5 Exceptions98
- About the Exception Model98
- Exception Types100
- Table 5-1 Exception Types100
- Exception Priority102
- Table 5-2 Priority-Based Actions of Exceptions102
- Table 5-3 Priority Grouping104
- Privilege and Stacks105
- Pre-Emption107
- Figure 5-1 Stack Contents after Pre-Emption107
- Table 5-4 Exception Entry Steps108
- Figure 5-2 Exception Entry Timing109
- Tail-Chaining110
- Figure 5-3 Tail-Chaining Timing110
- Late-Arriving111
- Figure 5-4 Late-Arriving Exception Timing111
- Exit113
- Table 5-5 Exception Exit Steps113
- Figure 5-5 Exception Exit Timing114
- Table 5-6 Exception Return Behavior115
- Resets116
- Table 5-7 Reset Actions116
- Table 5-8 Reset Boot-Up Behavior117
- Exception Control Transfer120
- Table 5-9 Transferring to Exception Processing120
- Setting up Multiple Stacks121
- Abort Model123
- Table 5-10 Faults124
- Table 5-11 Debug Faults126
- Table 5-12 Fault Status and Fault Address Registers127
- Activation Levels128
- Table 5-13 Privilege and Stack of Different Activation Levels128
- Table 5-14 Exception Transitions128
- Table 5-15 Exception Subtype Transitions129
- Flowcharts130
- Figure 5-6 Interrupt Handling Flowchart130
- Figure 5-7 Pre-Emption Flowchart131
- Figure 5-8 Return from Interrupt Flowchart132
Chapter 6 Clocking and Resets133
- Clocking134
- Table 6-1 Cortex-M3 Processor Clocks134
- Table 6-2 Cortex-M3 Macrocell Clocks134
- Resets136
- Table 6-3 Reset Inputs136
- Cortex-M3 Reset Modes137
- Table 6-4 Reset Modes137
- Figure 6-1 Reset Signals138
- Figure 6-2 Power-On Reset138
- Figure 6-3 Internal Reset Synchronization139
Chapter 7 Power Management141
- About Power Management142
- System Power Management143
- Table 7-1 Supported Sleep Modes143
- Figure 7-1 SLEEPING Power Control Example144
- Figure 7-2 SLEEPDEEP Power Control Example145
- Figure 7-3 WIC Mode Enable Sequence147
- Figure 7-4 Power down Timing Sequence148
- Figure 7-5 PMU, WIC, and Cortex-M3 Interconnect149
Chapter 8 Nested Vectored Interrupt Controller151
- About the NVIC152
- NVIC Programmer's Model153
- Table 8-1 NVIC Registers153
- Figure 8-1 Interrupt Controller Type Register Bit Assignments157
- Table 8-2 Interrupt Controller Type Register Bit Assignments158
- Figure 8-2 Auxiliary Control Register Bit Assignments158
- Table 8-3 Auxiliary Control Register Bit Assignments159
- Figure 8-3 Systick Control and Status Register Bit Assignments159
- Table 8-4 Systick Control and Status Register Bit Assignments160
- Table 8-5 Systick Reload Value Register Bit Assignments161
- Figure 8-4 Systick Reload Value Register Bit Assignments161
- Figure 8-5 Systick Current Value Register Bit Assignments161
- Table 8-6 Systick Current Value Register Bit Assignments162
- Table 8-7 Systick Calibration Value Register Bit Assignments162
- Figure 8-6 Systick Calibration Value Register Bit Assignments162
- Table 8-8 Interrupt Set-Enable Register Bit Assignments164
- Table 8-9 Interrupt Clear-Enable Register Bit Assignments164
- Table 8-10 Interrupt Set-Pending Register Bit Assignments165
- Table 8-11 Interrupt Clear-Pending Registers Bit Assignments166
- Table 8-12 Active Bit Register Bit Assignments166
- Figure 8-7 Interrupt Priority Registers 0-31 Bit Assignments167
- Table 8-13 Interrupt Priority Registers 0-31 Bit Assignments168
- Table 8-14 CPUID Base Register Bit Assignments168
- Figure 8-8 CPUID Base Register Bit Assignments168
- Table 8-15 Interrupt Control State Register Bit Assignments170
- Figure 8-9 Interrupt Control State Register Bit Assignments170
- Table 8-16 Vector Table Offset Register Bit Assignments172
- Figure 8-10 Vector Table Offset Register Bit Assignments172
- Table 8-17 Application Interrupt and Reset Control Register Bit Assignments173
- Figure 8-11 Application Interrupt and Reset Control Register Bit Assignments173
- Figure 8-12 System Control Register Bit Assignments175
- Table 8-18 System Control Register Bit Assignments176
- Table 8-19 Configuration Control Register Bit Assignments177
- Figure 8-13 Configuration Control Register Bit Assignments177
- Table 8-20 System Handler Priority Registers Bit Assignments179
- Figure 8-14 System Handler Priority Registers Bit Assignments179
- Table 8-21 System Handler Control and State Register Bit Assignments180
- Figure 8-15 System Handler Control and State Register Bit Assignments180
- Figure 8-16 Configurable Fault Status Registers Bit Assignments182
- Table 8-22 Memory Manage Fault Status Register Bit Assignments183
- Figure 8-17 Memory Manage Fault Status Register Bit Assignments183
- Figure 8-18 Bus Fault Status Register Bit Assignments184
- Table 8-23 Bus Fault Status Register Bit Assignments185
- Table 8-24 Usage Fault Status Register Bit Assignments186
- Figure 8-19 Usage Fault Status Register Bit Assignments186
- Figure 8-20 Hard Fault Status Register Bit Assignments187
- Table 8-25 Hard Fault Status Register Bit Assignments188
- Table 8-26 Debug Fault Status Register Bit Assignments189
- Figure 8-21 Debug Fault Status Register Bit Assignments189
- Table 8-27 Memory Manage Fault Address Register Bit Assignments190
- Table 8-28 Bus Fault Address Register Bit Assignments191
- Table 8-29 Auxiliary Fault Status Register Bit Assignments192
- Table 8-30 Software Trigger Interrupt Register Bit Assignments192
- Figure 8-22 Software Trigger Interrupt Register Bit Assignments192
- Level Versus Pulse Interrupts193
Chapter 9 Memory Protection Unit196
- About the MPU196
- MPU Programmer's Model197
- Table 9-1 MPU Registers197
- Table 9-2 MPU Type Register Bit Assignments198
- Figure 9-1 MPU Type Register Bit Assignments198
- Figure 9-2 MPU Control Register Bit Assignments199
- Table 9-3 MPU Control Register Bit Assignments200
- Table 9-4 MPU Region Number Register Bit Assignments201
- Figure 9-3 MPU Region Number Register Bit Assignments201
- Table 9-5 MPU Region Base Address Register Bit Assignments202
- Figure 9-4 MPU Region Base Address Register Bit Assignments202
- Table 9-6 MPU Region Attribute and Size Register Bit Assignments203
- Figure 9-5 MPU Region Attribute and Size Register Bit Assignments203
- Table 9-7 MPU Protection Region Size Field204
- MPU Access Permissions207
- Table 9-8 TEX, C, B Encoding207
- Table 9-9 Cache Policy for Memory Attribute Encoding208
- Table 9-10 AP Encoding208
- Table 9-11 XN Encoding208
- MPU Aborts209
- Updating an MPU Region210
- Interrupts and Updating the MPU213
Chapter 10 Core Debug216
- About Core Debug216
- Table 10-1 Core Debug Registers216
- Core Debug Registers217
- Table 10-2 Debug Halting Control and Status Register218
- Figure 10-1 Debug Halting Control and Status Register Bit Assignments218
- Figure 10-2 Debug Core Register Selector Register Bit Assignments220
- Table 10-3 Debug Core Register Selector Register221
- Table 10-4 Debug Exception and Monitor Control Register223
- Figure 10-3 Debug Exception and Monitor Control Register Bit Assignments223
- Core Debug Access Example226
- Using Application Registers in Core Debug227
- Table 10-5 Application Registers for Use in Core Debug227
Chapter 11 System Debug230
- About System Debug230
- System Debug Access231
- Figure 11-1 System Debug Access Block Diagram232
- System Debug Programmer's Model233
- Fpb234
- Table 11-1 FPB Register Summary235
- Table 11-2 Flash Patch Control Register Bit Assignments236
- Figure 11-2 Flash Patch Control Register Bit Assignments236
- Table 11-3 COMP Mapping238
- Figure 11-3 Flash Patch Remap Register Bit Assignments238
- Table 11-4 Flash Patch Remap Register Bit Assignments239
- Figure 11-4 Flash Patch Comparator Registers Bit Assignments239
- Table 11-5 Flash Patch Comparator Registers Bit Assignments240
- Dwt241
- Table 11-6 DWT Register Summary242
- Table 11-7 DWT Control Register Bit Assignments244
- Figure 11-5 DWT Control Register Bit Assignments244
- Table 11-8 DWT Current PC Sampler Cycle Count Register Bit Assignments247
- Table 11-9 DWT CPI Count Register Bit Assignments248
- Figure 11-6 DWT CPI Count Register Bit Assignments248
- Table 11-10 DWT Exception Overhead Count Register Bit Assignments249
- Figure 11-7 DWT Exception Overhead Count Register Bit Assignments249
- Figure 11-8 DWT Sleep Count Register Bit Assignments249
- Table 11-11 DWT Sleep Count Register Bit Assignments250
- Figure 11-9 DWT LSU Count Register Bit Assignments250
- Table 11-12 DWT LSU Count Register Bit Assignments251
- Table 11-13 DWT Fold Count Register Bit Assignments251
- Figure 11-10 DWT Fold Count Register Bit Assignments251
- Table 11-14 DWT Program Counter Sample Register Bit Assignments252
- Table 11-15 DWT Comparator Registers 0-3 Bit Assignments252
- Table 11-16 DWT Mask Registers 0-3 Bit Assignments253
- Figure 11-11 DWT Mask Registers 0-3 Bit Assignments253
- Table 11-17 Bit Functions of DWT Function Registers 0-3254
- Figure 11-12 DWT Function Registers 0-3 Bit Assignments254
- Table 11-18 Settings for DWT Function Registers256
- Itm258
- Table 11-19 ITM Register Summary258
- Table 11-20 ITM Trace Enable Register Bit Assignments260
- Table 11-21 ITM Trace Privilege Register Bit Assignments261
- Figure 11-13 ITM Trace Privilege Register Bit Assignments261
- Table 11-22 ITM Trace Control Register Bit Assignments262
- Figure 11-14 ITM Trace Control Register Bit Assignments262
- Figure 11-15 ITM Integration Write Register Bit Assignments263
- Table 11-23 ITM Integration Write Register Bit Assignments264
- Table 11-24 ITM Integration Read Register Bit Assignments264
- Figure 11-16 ITM Integration Read Register Bit Assignments264
- Table 11-25 ITM Integration Mode Control Register Bit Assignments265
- Table 11-26 ITM Lock Access Register Bit Assignments265
- Figure 11-17 ITM Integration Mode Control Bit Assignments265
- Table 11-27 ITM Lock Status Register Bit Assignments266
- Figure 11-18 ITM Lock Status Register Bit Assignments266
- Ahb-Ap267
- Table 11-28 AHB-AP Register Summary268
- Table 11-29 AHB-AP Control and Status Word Register Bit Assignments269
- Figure 11-19 AHB-AP Control and Status Word Register269
- Table 11-30 AHB-AP Transfer Address Register Bit Assignments270
- Table 11-31 AHB-AP Data Read/Write Register Bit Assignments271
- Table 11-32 AHB-AP Banked Data Register Bit Assignments271
- Table 11-33 AHB-AP Debug ROM Address Register Bit Assignments272
- Table 11-34 AHB-AP ID Register Bit Assignments272
- Figure 11-20 AHB-AP ID Register272
Chapter 12 Bus Interface274
- About Bus Interfaces274
- AMBA 3 Compliance275
- Icode Bus Interface276
- Table 12-1 Instruction Fetches276
- Dcode Bus Interface278
- System Interface279
- Unifying the Code Buses281
- Figure 12-1 Icode/Dcode Multiplexer281
- External Private Peripheral Interface282
- Access Alignment283
- Table 12-2 Bus Mapper Unaligned Accesses283
- Unaligned Accesses that Cross Regions284
- 12.10 Bit-Band Accesses285
- 12.11 Write Buffer286
- 12.12 Memory Attributes287
- Table 12-3 Memory Attributes287
- 12.13 AHB Timing Characteristics288
- Table 12-4 Interface Timing Characteristics288
Chapter 13 Debug Port289
- About the DP290
Chapter 14 Embedded Trace Macrocell292
- About the ETM292
- Figure 14-1 ETM Block Diagram293
- Table 14-1 ETM Core Interface Inputs and Outputs294
- Table 14-2 Miscellaneous Configuration Inputs294
- Table 14-3 Trace Port Signals295
- Table 14-4 Other Signals295
- Table 14-5 Clocks and Resets296
- Table 14-6 APB Interface Signals296
- Data Tracing297
- ETM Resources298
- Table 14-7 Cortex-M3 Resources298
- Trace Output301
- ETM Architecture302
- Figure 14-2 Return from Exception Packet Encoding302
- Table 14-8 Exception Tracing Mapping303
- Figure 14-3 Exception Encoding for Branch Packet304
- ETM Programmer's Model306
- Table 14-9 ETM Registers306
- Table 14-10 Boolean Function Encoding for Events312
- Table 14-11 Resource Identification Encoding313
- Table 14-12 Input Connections313
- Table 14-13 Trigger Output Connections313
Chapter 15 Embedded Trace Macrocell Interface315
- About the ETM Interface316
- CPU ETM Interface Port Descriptions317
- Table 15-1 ETM Interface Ports317
- Branch Status Interface320
- Table 15-2 Branch Status Signal Function320
- Table 15-3 Branches and Stages Evaluated by the Processor321
- Figure 15-1 Conditional Branch Backwards Not Taken322
- Figure 15-2 Conditional Branch Backwards Taken323
- Figure 15-3 Conditional Branch Forwards Not Taken323
- Figure 15-4 Conditional Branch Forwards Taken323
- Figure 15-5 Unconditional Branch Without Pipeline Stalls324
- Figure 15-6 Unconditional Branch with Pipeline Stalls324
- Table 15-4 Example of an Opcode Sequence325
- Figure 15-7 Unconditional Branch in Execute Aligned325
- Figure 15-8 Unconditional Branch in Execute Unaligned325
- Figure 15-9 Example of an Opcode Sequence327
Chapter 16 AHB Trace Macrocell Interface329
- About the AHB Trace Macrocell Interface330
- CPU AHB Trace Macrocell Interface Port Descriptions331
- Table 16-1 AHB Interface Ports331
Chapter 17 Trace Port Interface Unit334
- About the TPIU334
- Figure 17-1 TPIU Block Diagram (Non-ETM Version)335
- Figure 17-2 TPIU Block Diagram (ETM Version)336
- Table 17-1 Trace out Port Signals337
- Table 17-2 ATB Port Signals338
- Table 17-3 Miscellaneous Configuration Inputs338
- Table 17-4 APB Interface339
- TPIU Registers340
- Table 17-5 TPIU Registers340
- Table 17-6 Async Clock Prescaler Register Bit Assignments342
- Figure 17-3 Supported Sync Port Size Register Bit Assignments342
- Figure 17-4 Async Clock Prescaler Register Bit Assignments342
- Table 17-7 Selected Pin Protocol Register Bit Assignments343
- Figure 17-5 Selected Pin Protocol Register Bit Assignments343
- Table 17-8 Formatter and Flush Status Register Bit Assignments344
- Figure 17-6 Formatter and Flush Status Register Bit Assignments344
- Table 17-9 Formatter and Flush Control Register Bit Assignments345
- Figure 17-7 Formatter and Flush Control Register Bit Assignments345
- Table 17-10 Integration Test Register-ITATBCTR2 Bit Assignments347
- Figure 17-8 Integration Test Register-ITATBCTR2 Bit Assignments347
- Table 17-11 Integration Test Register-ITATBCTR0 Bit Assignments348
- Figure 17-9 Integration Test Register-ITATBCTR0 Bit Assignments348
- Figure 17-10 Integration Mode Control Register Bit Assignments348
- Table 17-12 Integration Mode Control Register Bit Assignments349
- Table 17-13 Integration Register : TRIGGER Bit Assignments349
- Figure 17-11 Integration Register : TRIGGER Bit Assignments349
- Table 17-14 Integration Register : FIFO Data 0 Bit Assignments350
- Figure 17-12 Integration Register : FIFO Data 0 Bit Assignments350
- Table 17-15 Integration Register : FIFO Data 1 Bit Assignments351
- Figure 17-13 Integration Register : FIFO Data 1 Bit Assignments351
- Serial Wire Output Connection353
- Figure 17-14 Dedicated Pin Used for TRACESWO353
- Figure 17-15 SWO Shared with TRACEPORT354
- Figure 17-16 SWO Shared with JTAG-TDO354
Chapter 18 Instruction Timing355
- About Instruction Timing356
- Processor Instruction Timings357
- Table 18-1 Instruction Timings357
- Load-Store Timings361
Chapter 19 AC Characteristics363
- Processor Timing Parameters364
- Table 19-1 Miscellaneous Input Ports Timing Parameters364
- Table 19-2 Low Power Input Ports Timing Parameters364
- Table 19-3 Interrupt Input Ports Timing Parameters365
- Table 19-4 AHB Input Ports Timing Parameters365
- Table 19-5 PPB Input Port Timing Parameters366
- Table 19-6 Debug Input Ports Timing Parameters366
- Table 19-7 Test Input Ports Timing Parameters367
- Table 19-8 ETM Input Port Timing Parameters367
- Table 19-9 Miscellaneous Output Ports Timing Parameters367
- Table 19-10 Low Power Output Ports Timing Parameters368
- Table 19-11 AHB Output Ports Timing Parameters368
- Table 19-12 PPB Output Ports Timing Parameters370
- Table 19-13 Debug Interface Output Ports Timing Parameters370
- Table 19-14 ETM Interface Output Ports Timing Parameters371
- Table 19-15 HTM Interface Output Ports Timing Parameters371
- Table 19-16 Test Output Ports Timing Parameters372
Appendix A Signal Descriptions374
- Clocks374
- A.1 Clocks374
- Table A-1 Clock Signals374
- Resets375
- A.2 Resets375
- Table A-2 Reset Signals375
- Miscellaneous376
- A.3 Miscellaneous376
- Table A-3 Miscellaneous Signals376
- Interrupt Interface378
- A.4 Interrupt Interface378
- Table A-4 Interrupt Interface Signals378
- Low Power Interface379
- Table A-5 Low Power Interface Signals379
- Icode Interface380
- Table A-6 Icode Interface380
- Dcode Interface381
- Table A-7 Dcode Interface381
- System Bus Interface382
- Table A-8 System Bus Interface382
- Private Peripheral Bus Interface383
- Table A-9 Private Peripheral Bus Interface383
- ITM Interface384
- Table A-10 ITM Interface384
- AHB-AP Interface385
- Table A-11 AHB-AP Interface385
- ETM Interface386
- Table A-12 ETM Interface386
- AHB Trace Macrocell Interface388
- Table A-13 HTM Interface388
- Test Interface389
- Table A-14 Test Interface389
- WIC Interface390
- A.15 WIC Interface390
- Table A-15 WIC Interface Signals390
Appendix B Revisions391
- Table B-1 Differences between Issue E and Issue F391
- Table B-2 Differences between Issue F and Issue G395

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