ARM ARM7TDMI User Manual Page 248
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Debug in Depth
B-30 Copyright © 1994-2001. All rights reserved. ARM DDI 0029G
Debug entry adds four addresses to the PC and every instruction adds one address. The
difference from breakpoint is that the instruction that caused the watchpoint has
executed and the program must return to the next instruction.
B.9.3 Watchpoint with another exception
If a watchpointed access simultaneously causes a Data Abort, the ARM7TDMI core
enters debug state in abort mode. Entry into debug is held off until the core changes into
abort mode and has fetched the instruction from the abort vector.
A similar sequence follows when an interrupt, or any other exception, occurs during a
watchpointed memory access. The ARM7TDMI core enters debug state in the mode of
the exception. The debugger must check to see if an exception has occurred by
examining the current and previous mode, in the CPSR and SPSR, and the value of the
PC. When an exception has taken place, you must give the user the choice of servicing
the exception before debugging.
Entry to debug state when an exception has occurred causes the PC to be incremented
by three instructions rather than four and this must be considered in return branch
calculation when exiting debug state. For example, suppose that an abort occurs on a
watchpointed access and ten instructions have been executed to determine this
eventuality. You can use the following sequence to return to program execution:
0 E1A00000; MOV R0, R0
1 E1A00000; MOV R0, R0
0 EAFFFFF0; B -16
This code forces a branch back to the abort vector, causing the instruction at that
location to be refetched and executed.
Note
After the abort service routine, the instruction that caused the abort and watchpoint is
refetched and executed. This triggers the watchpoint again and the ARM7TDMI core
re-enters debug state.
B.9.4 Debug request
Entry into debug state through a debug request is similar to a breakpoint. However,
unlike a breakpoint, the last instruction has completed execution and so must not be
refetched on exit from debug state. You can assume that entry to debug state adds three
addresses to the PC and every instruction executed in debug state adds one address.
For example, suppose that you have invoked a debug request and decided to return to
program execution straight away. You can use the following sequence:
- ARM7TDMI 1
- Contents 5
- Chapter 3 Memory Interface 6
- Chapter 5 Debug Interface 6
- Appendix A Signal Description 7
- Appendix B Debug in Depth 7
- List of Tables 10
- List of Figures 13
- • Further reading on page xxi 17
- • Feedback on page xxii 17
- About this document 18
- Preface 19
- Further reading 21
- Feedback 22
- Chapter 1 23
- Introduction 23
- 1.1 About the ARM7TDMI core 24
- 1.2 Architecture 27
- Figure 1-3 Main processor 30
- <Oprnd2> 32
- #32bit_Imm 32
- <reglist> 32
- [Rn, #+/-12bit_Offset] 37
- [Rn, +/-Rm] 37
- Register 37
- [Rn, #+/-8bit_Offset] 39
- [Rn, #+/-(8bit_Offset*4)] 39
- Operand 2 40
- Chapter 2 47
- Programmer’s Model 47
- 31 24 23 16 15 8 7 0 50
- Word at address A 50
- 2.4 Data types 52
- 2.5 Operating modes 53
- 2.6 Registers 54
- MOV PC, R14 62
- MOVS PC, R14_svc 62
- MOVS PC, R14_und 62
- SUBS PC, R14_abt, #4 62
- SUBS PC, R14_fiq, #4 63
- SUBS PC, R14_irq, #4 63
- SUBS PC, R14_abt, #8 63
- SUBS PC,R14_fiq,#4 64
- SUBS PC,R14_irq,#4 65
- LDR Rn,[R14_abt,#-8] 65
- SUBS PC,R14_abt,#4 66
- SUBS PC,R14_abt,#8 66
- 0x00000004 67
- 0x00000008 67
- 0x0000000C 67
- 0x00000010 68
- 0x00000014 68
- 0x00000018 68
- 0x0000001C 68
- 2.9 Interrupt latencies 69
- 2.10 Reset 70
- Chapter 3 71
- 3.2 Bus interface signals 73
- 3.3 Bus cycle types 74
- Figure 3-4 Internal cycles 78
- Figure 3-5 Merged IS cycle 79
- 3.4 Addressing signals 81
- Table 3-5 nTRANS encoding 83
- 1 Privileged 83
- 3.5 Address timing 84
- 3.6 Data timed signals 87
- DOUT[31:0] 89
- XDATA[31:0] 89
- DIN[31:0] 89
- Figure 3-18 Memory access 95
- Figure 3-20 Data replication 98
- 3.7 Stretching access times 99
- Memory Interface 100
- 3.9 Privileged mode access 102
- Figure 3-22 Reset sequence 103
- Chapter 4 105
- Coprocessor Interface 105
- 4.1 About coprocessors 106
- Signal Direction Meaning 110
- Table 4-2 Handshaking signals 110
- ARM core 116
- Coprocessor 116
- 4.7 Undefined instructions 120
- 4.8 Privileged instructions 121
- Chapter 5 123
- Debug Interface 123
- 5.1 About the debug interface 124
- EmbeddedICE 127
- Main processor 127
- TAP controller 127
- 5.3 Debug interface signals 128
- Figure 5-3 Debug state entry 129
- MOV PC, #0 133
- 5.7 Disabling EmbeddedICE 137
- MRC CP14, 0, Rd, C0, C0, 0 139
- MCR CP14, 0, Rn, C1, C0, 0 139
- MRC CP14, 0, Rd, C1, C0, 0 139
- Chapter 6 143
- Instruction Cycle Timings 143
- SUB PC,R14,#4 to MOV PC,R14 146
- 6.3 Thumb branch with link 147
- 6.4 Branch and Exchange 148
- 6.5 Data operations 149
- Thumb state 150
- 6.7 Load register 154
- 6.8 Store register 156
- 6.9 Load multiple registers 157
- 6.10 Store multiple registers 159
- 6.11 Data swap 160
- 6.19 Unexecuted instructions 170
- Chapter 7 173
- AC and DC Parameters 173
- Figure 7-1 General timing 176
- 7.7 Output 3-state timing 182
- 7.10 Configuration pin timing 185
- 7.16 Breakpoint timing 192
- TCK to ECLK delay Maximum 193
- 7.20 Reset period timing 196
- In Table 7-23: 200
- 7.25 DC parameters 206
- Appendix A 207
- Signal Description 207
- A.1 Signal description 208
- A.1.3 Signals 209
- Appendix B 219
- Debug in Depth 219
- Scan chain 2 222
- B.1.2 TAP state machine 223
- B.3 Pullup resistors 225
- B.4 Instruction register 226
- B.5 Public instructions 227
- B.6 Test data registers 232
- Figure B-4 Input scan cell 235
- B.7 The ARM7TDMI core clocks 240
- Internal cycles 246
- 0 E0802000; ADD R2, R0, R0 247
- 1 E1826001; ORR R6, R2, R1 247
- MOV R0, R0 247
- SUB PC, PC, #28 247
- 0 E1A00000; MOV R0, R0 248
- 1 E1A00000; MOV R0, R0 248
- 0 EAFFFFF0; B -16 248
- 0 EAFFFFFA; B -6 249
- - (4+N+3S) 249
- - (3+N+3S) 249
- B.11 Scan chain cell data 251
- B.11.2 Scan chain 1 cells 255
- 31 D[30] Input/output 257
- 32 D[31] Input/output 257
- 33 BREAKPT Input 257
- Number Signal Type 257
- B.12 The watchpoint registers 258
- 0xFFFFFFFF 260
- B.13 Programming breakpoints 263
- 0xDEEEDEEE 264
- 0x00000000 264
- B.14 Programming watchpoints 265
- INTDIS DBGRQ DBGACK 266
- B.18 EmbeddedICE timing 272
- B.19 Programming Restriction 273
- Glossary 275
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