ARM ARM7TDMI User Manual Page 185
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Instruction Cycle Timings
ARM DDI 0234B Copyright © 2001 ARM Limited. All rights reserved. 7-7
7.3 Branch and ARM branch with link
Any ARM or Thumb branch, and an ARM branch with link operation takes three
cycles:
1. During the first cycle, a branch instruction calculates the branch destination while
performing a prefetch from the current PC. This prefetch is done in all cases
because, by the time the decision to take the branch has been reached, it is already
too late to prevent the prefetch.
2. During the second cycle, the ARM7TDMI-S core performs a Fetch from the
branch destination. The return address is stored in r14 if the link bit is set.
3. During the third cycle, the ARM7TDMI-S core performs a Fetch from the
destination + i, refilling the instruction pipeline. When the instruction is a branch
with link, r14 is modified (4 is subtracted from it) to simplify return to
MOV PC,R14.
This modification ensures subroutines of the type
STM..{R14} LDM..{PC}
work
correctly.
Table 7-3 shows the cycle timings, where:
pc Is the address of the branch instruction.
pc’ Is an address calculated by the ARM7TDMI-S core.
(pc’) Are the contents of that address.
Note
This data applies only to branches in ARM and Thumb states, and to branch with link
in ARM state.
Table 7-3 Branch instruction cycle operations
Cycle Address Size Write Data TRANS[1:0] Prot0
1 pc+2i w/h 0 (pc + 2i) N cycle 0
2 pc’ w’/h’ 0 (pc’) S cycle 0
3 pc’+i w’/h’ 0 (pc’ + i) S cycle 0
pc’+2i w’/h’ - - - -
- ARM7TDMI-S 1
- Contents 3
- Chapter 3 Memory Interface 4
- Chapter 6 ETM Interface 5
- Chapter 8 AC Parameters 5
- List of Tables 7
- List of Figures 10
- • Feedback on page xvi 11
- About this document 12
- Preface 13
- Other publications 15
- Architecture 15
- Feedback 16
- Chapter 1 17
- Introduction 17
- 1.2 ARM7TDMI-S architecture 20
- Figure 1-3 ARM7TDMI-S core 23
- 1.4.1 ARM instruction summary 26
- [Rn, #+/-12bit_Offset] 29
- [Rn, +/-Rm] 29
- [Rn, #+/-12bit_Offset]! 29
- [Rn, +/-Rm]! 29
- , is shown in Table 1-4 30
- [Rn, #+/-8bit_Offset] 31
- Register 31
- [Rn, #+/-(8bit_Offset*4)] 32
- Post-indexed 32
- Fields 33
- , are shown in Table 1-10 33
- Condition fields 33
- , are shown in Table 1-11 33
- Halfword 36
- POP <reglist> 38
- POP <reglist, PC> 38
- SWI 8bit_Imm 38
- 0x7F1F0F0F 40
- Chapter 2 43
- Programmer’s Model 43
- 2.3 Memory formats 46
- 2.4 Instruction length 48
- 2.5 Data types 49
- 2.6 Operating modes 50
- 2.7 Registers 51
- Table 2-2 PSR mode bit values 59
- MOV PC, R14 61
- MOVS PC, R14_svc 61
- MOVS PC, R14_und 61
- SUBS PC, R14_abt, #4 61
- SUBS PC, R14_fiq, #4 62
- SUBS PC, R14_irq, #4 62
- SUBS PC, R14_abt, #8 62
- UNPREDICTABLE 62
- SUBS PC,R14_fiq,#4 63
- SUBS PC,R14_abt,#8 65
- MOVS PC,R14_und 65
- 2.10 Interrupt latencies 68
- 2.11 Reset 69
- Chapter 3 71
- Memory Interface 71
- 3.2 Bus interface signals 73
- 3.3 Bus cycle types 74
- Table 3-2 Burst types 77
- Figure 3-5 Merged I-S cycle 79
- 3.4 Addressing signals 80
- 3.4.6 CPTBIT 82
- 3.5 Data timed signals 83
- Figure 3-6 Data replication 86
- Figure 3-7 Use of CLKEN 87
- Chapter 4 89
- 4.1 About coprocessors 90
- Table 4-2 Handshaking signals 94
- Signal Direction Meaning 94
- 4.5 Connecting coprocessors 99
- Coprocessor Interface 100
- 4.7 Undefined instructions 103
- 4.8 Privileged instructions 104
- Chapter 5 105
- Debugging Your System 105
- 5.2 Controlling debugging 109
- 5.3 Entry into debug state 111
- Figure 5-3 Debug state entry 112
- ARM7TDMI-Smacrocell 115
- 5.4 Debug interface 116
- EmbeddedICE-RT 118
- 5.7 Disabling EmbeddedICE-RT 120
- 5.9 Monitor mode debugging 122
- 0 RW...100 124
- MRC CP14, 0, Rd, C0, C0 125
- MCR CP14, 0, Rn, C1, C0 125
- MRC CP14, 0, Rd, C1, C0 126
- 5.12 The TAP controller 130
- 5.13 Public JTAG instructions 132
- 011112272831 135
- Part number 135
- Manufacturer identity 1 135
- 0x7f1f0f0f 136
- 5.15 Scan timing 140
- 31 DATA[30] Input/output 142
- 32 DATA[31] Input/output 142
- 33 DBGBREAK Input 142
- Number Signal Type 142
- 5.17 Exit from debug state 146
- 0 E0802000; ADD R2, R0, R0 148
- 1 E1826001; ORR R6, R2, R1 148
- MOV R0, R0 148
- SUB PC, PC, #28 148
- - (4 + N + 3S) 150
- - (3 + N + 3S) 150
- 8 67 5 34 2 01 154
- 5.21 Programming breakpoints 157
- 0xffffffff 158
- 0xdfffdfff 158
- 0x00000000 158
- 5.22 Programming watchpoints 159
- 5.23 Abort status register 160
- 5.24 Debug control register 161
- 5.25 Debug status register 164
- 5.27 EmbeddedICE-RT timing 169
- Chapter 6 171
- ETM Interface 171
- 6.1 About the ETM interface 172
- 6.4 Clocks and resets 176
- 6.5 Debug request wiring 177
- Chapter 7 179
- Instruction Cycle Timings 179
- MOV PC,R14 185
- STM..{R14} LDM..{PC} 185
- 7.4 Thumb branch with link 186
- 7.5 Branch and exchange 187
- 7.6 Data operations 188
- 7.8 Load register 192
- 7.9 Store register 194
- 7.10 Load multiple registers 195
- 7.11 Store multiple registers 197
- 7.12 Data swap 198
- 7.20 Unexecuted instructions 208
- Chapter 8 209
- AC Parameters 209
- 8.1 Timing diagrams 210
- Figure 8-2 Coprocessor timing 212
- 8.1.4 Debug timing 213
- 8.1.5 Scan timing 214
- Figure 8-5 Scan timing 215
- Appendix A 219
- Signal Descriptions 219
- A.1 Signal descriptions 220
- Appendix B 227
- ARM7TDMI 227
- B.1 Interface signals 228
- B.2 ATPG scan interface 232
- B.3 Timing parameters 233
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