Cortex-A8 Technical Reference Manual - ARM Information Center

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5.1 About program flow prediction Program Flow Prediction The processor contains program flow prediction hardware, also known as branch prediction. With program flow prediction disabled, all taken branches incur a 13-cycle penalty. With program flow prediction enabled, all mispredicted branches incur a 13-cycle penalty. To avoid this penalty, the branch prediction hardware operates at the front of the instruction pipeline. The branch prediction hardware consists of: • a 512-entry 2-way set associative Branch Target Buffer (BTB) • a 4096-entry Global History Buffer (GHB) • an 8-entry return stack. An unpredicted branch executes in the same way as a branch that is predicted as not taken. Incorrect or invalid prediction of the branch prediction or target address causes the pipeline to flush, invalidating all of the following instructions. ARM DDI 0344K Copyright © 2006-2010 ARM Limited. All rights reserved. 5-2 ID060510 Non-Confidential
5.2 Predicted instructions Program Flow Prediction This section shows the instructions that the processor predicts. Unless otherwise specified, the list applies to ARM, Thumb-2, and ThumbEE instructions. See the ARM Architecture Reference Manual for more information about instructions or addressing modes. The flow prediction hardware predicts the following instructions: • B conditional • B unconditional • BL • BLX(1) immediate The BL and BLX(1) instructions act as function calls and push the return address and ARM or Thumb state onto the return stack. • BLX(2) register The BLX(2) instruction acts as a function call and pushes the return address and ARM or Thumb state onto the return stack. • BX The BX r14 instruction acts as a function return and pops the return address and ARM or Thumb state from the return stack. • LDM(1) with PC in the register list in ARM state The LDM instruction with r13 specified as the base register acts as a function return and pops the return address and ARM or Thumb state from the return stack. • POP with PC in register list in Thumb state The POP instruction acts as a function return and pops the return address and ARM or Thumb state from the return stack. • LDM with PC in register list in Thumb or ThumbEE state The LDM instruction with r13 specified as the base register, or r9 specified as the base register in ThumbEE state acts as a function return and pops the return address and ARM or Thumb state from the return stack. • LDR with PC destination The LDR instruction with r13 specified as the base register, or r9 specified as the base register in ThumbEE state, acts as function return and pops the return address and ARM or Thumb state from the return stack. • PC-destination data-processing operations in ARM state In ARM state, the second operand of a data-processing instruction can be a 32-bit immediate value, an immediate shift value, or a register shift value. An instruction with an immediate shift value or a register shift value is predicted. An instruction with a 32-bit immediate value is not predicted. For example: — MOV pc, r10, LSL r3 is predicted — ADD pc, r0, r1, LSL #2 is predicted — ADD pc, r4, #4 is not predicted. There is no restriction on the opcode predicted, but a majority of opcodes do not make sense for branch-type instructions. Usually only MOV, ADD, and SUB are useful. ARM DDI 0344K Copyright © 2006-2010 ARM Limited. All rights reserved. 5-3 ID060510 Non-Confidential
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Copyright © 2006-2010 ARM Limited.
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Web Address http://www.arm.com ARM
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Contents 2.14 The program status re
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Contents 16.6 Instruction-specific
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List of Tables Table 3-16 Debug Fea
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List of Tables Table 3-136 Secure o
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List of Tables Table 12-59 Values t
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List of Figures Cortex-A8 Technical
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List of Figures Figure 3-77 BTB arr
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List of Figures Figure 15-16 CTI Ch
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About this manual Product revision
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old Highlights interface elements,
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Feedback Feedback on the product Fe
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1.1 About the processor Introductio
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1.3 Components of the processor L1
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1.3.6 NEON 1.3.7 ETM The NEON unit
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1.5 Debug Introduction The processo
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1.7 Configurable options Table 1-1
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Introduction • The various data a
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1.9.6 r2p0-r2p1 1.9.7 r2p1-r2p2 1.9
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Chapter 2 Programmers Model This ch
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2.2 Thumb-2 instruction set Program
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Bits Field Function Programmers Mod
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2.4 Jazelle Extension 2.4.1 Jazelle
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2.5 Security Extensions architectur
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2.6 Advanced SIMD architecture Prog
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2.8 Processor operating states 2.8.
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2.10 Memory formats 2.10.1 Byte-inv
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2.12 Operating modes Programmers Mo
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System and User r0 r1 r2 r3 r4 r5 r
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2.14 The program status registers 2
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2.14.5 The GE[3:0] bits Programmers
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Mode bits Programmers Model M[4:0]
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2.15 Exceptions 2.15.1 Exception en
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2.15.5 Interrupt request 2.15.6 Abo
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This restores both the PC and the C
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2.15.13 Exception priorities Progra
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2.17 Hardware consideration for Sec
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SECMONOUT[78] instruction caches at
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Chapter 3 System Control Coprocesso
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System Control Coprocessor Register
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3.1.3 MMU control and configuration
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3.2 System control coprocessor regi
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CRn Op1 CRm Op2 Register or operati
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3.2.2 c0, Main ID Register System C
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3.2.4 c0, TCM Type Register 3.2.5 c
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3.2.7 c0, Processor Feature Registe
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• accessible in privileged modes
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System Control Coprocessor Table 3-
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Bits Field Function [11:8] L1 Harva
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Bits Field Function [11:8] Harvard
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31 28 27 24 23 20 19 16 15 12 11 8
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Table 3-30 shows the results of att
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System Control Coprocessor 31 28 27
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Table 3-36 shows the results of att
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• accessible in privileged modes
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CSSR Size 3.2.24 c0, Cache Size Sel
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System Control Coprocessor 31 30 29
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MCR p15, 0, , c1, c0, 0 ; Write Con
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Bits Field [19] Clock stop request
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Bits Field Security State NS S Tabl
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3.2.28 c1, Secure Configuration Reg
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AW EA Function Table 3-55 shows the
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3.2.32 c2, Translation Table Base R
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System Control Coprocessor Figure 3
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Bits Field Function 3.2.35 c5, Data
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3.2.36 c5, Instruction Fault Status
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3.2.38 c6, Data Fault Address Regis
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System Control Coprocessor Note •
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System Control Coprocessor Figure 3
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3.2.41 c8, TLB operations The data
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Figure 3-38 shows the bit arrangeme
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EN b 3.2.44 c9, Count Enable Clear
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EN b 3.2.46 c9, Software Increment
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EN b 3.2.48 c9, Cycle Count Registe
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EN b Table 3-96 shows the results o
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Value Description 0x44 Any cacheabl
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DBGEN || NIDEN 3.2.51 c9, User Enab
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EN 3.2.53 c9, Interrupt Enable Clea
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Figure 3-48 shows the bit arrangeme
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3.2.55 c9, L2 Cache Auxiliary Contr
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Page 183 and 184: The PLE Identification and Status R
Page 187 and 188: 3.2.62 c11, PLE enable commands U b
Page 189 and 190: Bits Field Function System Control
Page 191 and 192: U bit PLE bit Table 3-129 shows the
Page 193 and 194: U bit PLE bit System Control Coproc
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Page 197 and 198: 3.2.70 c12, Interrupt Status Regist
Page 199 and 200: The FCSE PID Register is: • a rea
Page 203 and 204: TLB CAM read/write TLB ATTR read/wr
Page 205 and 206: MCR p15 0, , c15, c3, 4 ; I-L1 TLB
Page 207 and 208: 31 27 26 22 21 0 Reserved L1 Data 0
Page 209 and 210: System Control Coprocessor The L1 H
Page 211 and 212: 3.2.78 c15, L1 data array operation
Page 213 and 214: Instruction L1 Data 0 register Inst
Page 215 and 216: Parity/ECC RAM read/write Data RAM
Page 217 and 218: 3.2.82 c15, L2 parity/ECC array ope
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Page 221 and 222: 4.1 About unaligned and mixed-endia
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Page 231 and 232: 5.4 Guidelines for optimal performa
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Page 235 and 236: 6.1 About the MMU Memory Management
Page 237 and 238: 6.3 16MB supersection support Memor
Page 239 and 240: 6.5 External aborts 6.5.1 External
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Page 243 and 244: 7.1 About the L1 memory system Leve
Page 245 and 246: 7.2.6 Instruction cache maintenance
Page 247 and 248: L1 inner policy a L2 outer policy N
Page 249 and 250: 7.5 Data cache features 7.5.1 Data
Page 251 and 252: 7.7 Hardware support for virtual al
Page 253 and 254: Chapter 8 Level 2 Memory System Thi
Page 255 and 256: 8.2 Cache organization 8.2.1 L2 cac
Page 257 and 258: 8.3 Enabling and disabling the L2 c
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Page 265 and 266: 8.7 Parity and error correction cod
Page 267 and 268: 9.1 About the external memory inter
Page 269 and 270: Integer data and CP14 writes Noncac
Page 271 and 272: 9.4 AXI data read/write transaction
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LA Last Access External Memory Inte
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10.1 Clock domains 10.1.1 AXI clock
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10.2 Reset domains 10.2.1 Power-on
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REFCLK (PLL input) nPORESET ARESETn
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10.3 Power control 10.3.1 Dynamic p
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Clock, Reset, and Power Control the
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ATB APB I/O clamp I/O clamp L/S = L
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ATB APB I/O clamp I/O clamp LS = Le
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Clock, Reset, and Power Control 3.
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Powering up the debug and ETM domai
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7. Perform a normal software reset
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Clock, Reset, and Power Control 5.
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Chapter 11 Design for Test This cha
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In L1 MBIST Instruction Register Fi
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Note Do not test the CAMBIST arrays
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• number of rows of the L2 data,
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Design for Test Not all row setting
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In Design for Test Figure 11-4 show
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Design for Test When testing the ta
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CLK ARESETn MBISTMODE MBISTSHIFT MB
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End-of-test datalog retrieval Desig
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Pattern N RWRXMARCH 8N Row-fast Sta
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4. rscan array, data_seed = invert.
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3. R_, W, R, decr. 4. rscan data fr
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• the data after pass 1 of XADDRB
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(1 + (2 17)) 2 17 = 4,587,520 cycle
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processor input ports WEXTEST WINTE
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Design for Test toggling during shi
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12.1 Debug systems 12.1.1 Debug hos
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12.2.3 Security extensions and debu
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Instruction Mnemonic Description 12
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12.3.6 Power domains and debug 12.3
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Table 12-5 shows the APB interface
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12.4 Debug register descriptions Te
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MRC p14, 0, , c0, c0, 0 ; Read Debu
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31 30 29 28 27 26 25 24 23 22 21 20
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Bits Field Function [21:20] DTR acc
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Bits Field Function To access the D
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12.4.7 Watchpoint Fault Address Reg
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Bits Access Normal address [2] RW V
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12.4.12 Debug Run Control Register
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Table 12-23 shows how the bit value
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BVR[22:20] Meaning b011 The corresp
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Bits Field Function [15:14] Secure
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12.4.18 Operating System Lock Statu
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Debug • The sequence can be aband
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12.5 Management registers Offset Th
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Offset Register number Mnemonic Fun
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Bits Field Function [5] nDMAIRQ nDM
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12.5.7 Claim Tag Clear Register 12.
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12.5.10 Authentication Status Regis
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Table 12-45 shows fields that are i
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12.6 Debug events 12.6.1 Software d
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12.6.5 Watchpoint debug events If a
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Table 12-53 shows the values in the
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12.8 Debug state 12.8.1 Entering de
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12.8.4 Writing to the CPSR in debug
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Mode SCR[0] For CP15 instructions,
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12.8.9 Leaving debug state Imprecis
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12.9.3 Cache usage profiling Debug
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Note DBGPWRDWNREQ must be tied LOW
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If software running on the processo
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Rules for accessing the DCC At the
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} While the processor is running, i
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Debug Table 12-59 Values to write t
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12.11.4 Debug state entry Example 1
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} // Step 1. Update the CPSR value
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Writing the CPSR in debug state Exa
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Debug Example 12-21 Reading a word
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} // Step 9. Check for aborts. abor
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12.12 Debugging systems with energy
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MOV r0, r4 POP {r4, pc} Example 12-
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Chapter 13 NEON and VFP Programmers
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13.2 General-purpose registers 13.2
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13.3 Short vectors 13.3.1 About reg
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13.3.2 Operations using register ba
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NEON and VFP Programmers Model The
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Note All hardware ID information is
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Bits Field Function [12:8] - Reserv
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NEON and VFP Programmers Model Tabl
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13.6 Compliance with the IEEE 754 s
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Underflow NEON and VFP Programmers
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14.1 About the ETM 14.1.1 ETM featu
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14.1.3 NEON Bridge and bus matrix A
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14.3 ETM register summary The ETM r
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Bits Field Function [11:8] Major ET
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14.4.4 Peripheral Identification Re
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See the ETM Architecture Specificat
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Embedded Trace Macrocell Table 14-1
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14.5.3 Enabling events 14.5.4 Addre
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14.7 Context ID tracing Embedded Tr
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14.9 Idle state control Embedded Tr
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Chapter 15 Cross Trigger Interface
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CTICHIN[0] CTICHIN[1] CTICHIN[2] CT
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15.2 Trigger inputs and outputs Tri
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15.3 Connecting asynchronous channe
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15.5 CTI register summary Address o
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15.6 CTI register descriptions This
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15.6.4 CTI Application Trigger Clea
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Table 15-10 shows how the bit value
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15.6.12 ASIC Control Register, ASIC
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15.7 CTI Integration Test Registers
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15.7.4 ITTRIGOUTACK, 0xEF0 15.7.5 I
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Cross Trigger Interface Table 15-26
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15.8.3 Device Type Identifier, 0xFC
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Cross Trigger Interface Table 15-31
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16.1 About instruction cycle timing
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Instruction Cycle Timing Example 16
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Table 16-4 shows the operation of m
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Table 16-9 shows the operation of l
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d. See Load/store instructions on p
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Instruction Cycle Timing Table 16-1
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16.4 Other pipeline-dependent laten
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16.4.5 Conditional instructions Ins
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16.6 Instruction-specific schedulin
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Instruction Cycle Timing VNEG Dd,Dm
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VMLA a VMLS a VMLAa VMLSa VQDMLAa V
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VSLI VSRI 16.6.5 Advanced SIMD floa
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16.6.6 Advanced SIMD byte permute i
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Instruction Table 16-23 shows the o
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Instruction VST3 3-reg (unaligned)
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Instruction VLD3 3-reg (unaligned)
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Instruction Single precision cycles
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• FMACS, FNMACS • FMSCS, FNMSCS
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is dual issued with previous instru
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17.1 About setup and hold times AC
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17.2 AXI interface Table 17-2 shows
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17.3 ATB and CTI interfaces Table 1
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AC Characteristics Table 17-4 Timin
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17.6 L2 preload interface AC Charac
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17.8 Miscellaneous signals AC Chara
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A.1 AXI interface Signal Descriptio
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A.3 MBIST and DFT interface A.3.1 M
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A.4 Preload engine interface Table
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A.6 Miscellaneous signals Table A-7
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Signal I/O Reset Description CFGNMF
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Signal I/O Reset Description DBGNOP
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Appendix B Instruction Mnemonics Th
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Instruction Mnemonics Table B-1 Adv
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Appendix C Revisions This appendix
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Revisions Added text to clarify des
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Glossary This glossary describes so
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Glossary Automatic Test Pattern Gen
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Big-endian memory Memory in which:
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Conditional execution Glossary incl
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Glossary Embedded Trace Macrocell (
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Illegal instruction An instruction
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Glossary NaN Not a number. A symbol
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Glossary Significand The component
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Glossary Watchpoint A watchpoint is
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