Intel Computer Hardware 80200 Instrukcja Użytkownika Strona 268
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B-40 March, 2003 Developer’s Manual
Intel
®
80200 Processor based on Intel
®
XScale
™
Microarchitecture
Optimization Guide
B.5.3 Scheduling Multiply Instructions
Multiply instructions can cause pipeline stalls due to either resource conflicts or result latencies.
The following code segment would incur a stall of 0-3 cycles depending on the values in registers
r1, r2, r4 and r5 due to resource conflicts.
mul r0, r1, r2
mul r3, r4, r5
The following code segment would incur a stall of 1-3 cycles depending on the values in registers
r1 and r2 due to result latency.
mul r0, r1, r2
mov r4, r0
Note that a multiply instruction that sets the condition codes blocks the whole pipeline. A 4 cycle
multiply operation that sets the condition codes behaves the same as a 4 cycle issue operation.
Consider the following code segment:
muls r0, r1, r2
add r3, r3, #1
sub r4, r4, #1
sub r5, r5, #1
The add operation above would stall for 3 cycles if the multiply takes 4 cycles to complete. It is
better to replace the code segment above with the following sequence:
mul r0, r1, r2
add r3, r3, #1
sub r4, r4, #1
sub r5, r5, #1
cmp r0, #0
Please refer to Section 14.4, “Instruction Latencies” to get the instruction latencies for various
multiply instructions. The multiply instructions should be scheduled taking into consideration these
instruction latencies.
- 80200 Processor based on 1
- Microarchitecture 1
- Contents 3
- A Compatibility: Intel 9
- Introduction 17
- 1.1.2 Features 18
- 1.2.1 Number Representation 21
- 1.3 Other Relevant Documents 22
- Programming Model 23
- 2.2.5 Base Register Update 24
- 2.3.1 DSP Coprocessor 0 (CP0) 25
- 2.3.2 New Page Attributes 31
- 2.3.4 Event Architecture 34
- 2.3.4.3 Prefetch Aborts 35
- 2.3.4.4 Data Aborts 36
- Contents 38
- Memory Management 39
- 3.2 Architecture Model 40
- 3.2.3 Exceptions 42
- 3.4 Control 44
- 3.4.3 Locking Entries 45
- Instruction Cache 49
- 4.2 Operation 50
- 4.2.3 Fetch Policy 51
- 4.2.5 Parity Protection 52
- 4.3 Instruction Cache Control 54
- Branch Target Buffer 59
- 5.1.1 Reset 60
- 5.1.2 Update Policy 60
- 5.2 BTB Control 61
- Data Cache 63
- 6.2.3 Cache Policies 67
- 6.2.3.2 Read Miss Policy 68
- 6.2.3.3 Write Miss Policy 69
- 6.2.5 Parity Protection 70
- 6.2.6 Atomic Accesses 70
- 6.3.2 Enabling/Disabling 71
- Bits Description Notes 81
- 7.2 CP15 Registers 82
- 7.2.5 Register 4: Reserved 87
- • translation faults 89
- • domain faults 89
- • permission faults 89
- 7.3 CP14 Registers 98
- Configuration 100
- System Management 101
- 8.2 Processor Reset 103
- 8.2.2 Reset Effect on Outputs 104
- 8.3 Power Management 105
- Interrupts 107
- 9.3 Programmer Model 108
- 9.3.1 INTCTL 109
- 9.3.2 INTSRC 110
- 9.3.3 INTSTR 111
- External Bus 113
- 10.2 Signal Description 115
- 10.2.1 Request Bus 116
- 10.2.2 Data Bus 118
- 10.2.3 Critical Word First 119
- 10.2.4 Configuration Pins 120
- 10.2.5 Multimaster Support 121
- 10.2.6 Abort 123
- 10.2.7 ECC 124
- 10.3 Examples 126
- 10.3.4 Word Write 129
- 10.3.5.1 Write Burst 131
- 10.3.6 Write Burst, Coalesced 132
- 10.3.7 Pipelined Accesses 133
- 10.3.8 Locked Access 134
- 10.3.9 Aborted Access 135
- 10.3.10 Hold 136
- Bus Controller 137
- 11.3 Error Handling 138
- 11.3.2 ECC Errors 139
- 11.4 Programmer Model 141
- 11.4.2 ECC Error Registers 145
- Performance Monitoring 147
- 12.4.1 Managing PMNC 151
- 12.7 Examples 158
- Software Debug 159
- 13.3 Introduction 160
- 13.4.1 Global Enable Bit (GE) 162
- 13.4.2 Halt Mode Bit (H) 162
- 13.4.4 Sticky Abort Bit (SA) 163
- 13.5 Debug Exceptions 164
- 13.5.2 Monitor Mode 166
- 13.6 HW Breakpoint Resources 167
- 13.6.2 Data Breakpoints 168
- 13.7 Software Breakpoints 169
- 13.8.2 Overflow Flag (OV) 172
- 13.8.3 Download Flag (D) 172
- 13.9 Transmit Register (TX) 174
- 13.10 Receive Register (RX) 174
- 13.11 Debug JTAG Access 175
- 13.11.2 SELDCSR JTAG Register 176
- 13.11.2.1 DBG.HLD_RST 177
- 13.11.3 DBGTX JTAG Command 178
- 13.11.4 DBGTX JTAG Register 179
- 13.11.5 DBGRX JTAG Command 179
- 13.11.6 DBGRX JTAG Register 180
- 13.11.6.1 RX Write Logic 181
- 13.11.6.2 DBGRX Data Register 182
- 13.11.6.3 DBG.RR 182
- 13.11.6.4 DBG.V 183
- 13.11.6.5 DBG.RX 183
- 13.11.6.6 DBG.D 183
- 13.11.6.7 DBG.FLUSH 183
- 13.12 Trace Buffer 184
- 13.13 Trace Buffer Entries 186
- 13.13.1.3 Address Bytes 189
- 13.13.2 Trace Buffer Usage 190
- 13.14.1 LDIC JTAG Command 192
- 13.14.3 LDIC Cache Functions 194
- Debugger Actions 201
- Debug Handler Actions 201
- • a debug handler; 205
- • External memory 209
- 13.15.2.4 High-Speed Download 210
- • turn off all breakpoints; 211
- • invalidate the btb; 211
- Performance Considerations 213
- 14.2 Branch Prediction 214
- 14.3 Addressing Modes 214
- 14.4 Instruction Latencies 215
- • Minimum Resource Latency 216
- 14.4.8 Semaphore Instructions 221
- 14.4.11 Thumb* Instructions 221
- Compatibility: Intel 223
- 80200 Processor 223
- A.3 Architecture Deviations 225
- A.3.4 Write Buffer Behavior 226
- A.3.5 External Aborts 226
- A.3.6 Performance Differences 227
- Optimization Guide B 229
- B.2 Intel 230
- 80200 Processor Pipeline 230
- F1 F2 ID RF X1 X2 231
- M1 M2 Mx 231
- B.2.1.5. Use of Bypassing 232
- B.2.2.2. Pipeline Stalls 233
- B.2.3 Main Execution Pipeline 234
- Optimization Guide 235
- B.2.4 Memory Pipeline 236
- B.3 Basic Optimizations 237
- B.3.1.2. Optimizing Branches 238
- B.3.2 Bit Field Manipulation 241
- B.4.1 Instruction Cache 245
- • Interrupt handlers 246
- • Real time clock handlers 246
- • OS critical code 246
- B.4.2 Data and Mini Cache 247
- B.4.2.4. Creating On-chip RAM 248
- B.4.2.5. Mini-data Cache 249
- B.4.2.6. Data Alignment 250
- B.4.2.7. Literal Pools 251
- B.4.3 Cache Considerations 252
- B.4.4 Prefetch Considerations 253
- B.4.4.8. Cache Blocking 259
- B.4.4.9. Prefetch Unrolling 259
- B.4.4.10. Pointer Prefetch 260
- B.4.4.11. Loop Interchange 261
- B.4.4.12. Loop Fusion 261
- B.5 Instruction Scheduling 263
- B.6 Optimizing C Libraries 273
- B.7 Optimizations for Size 273
- Test Features C 275
- Test Features 276
- C.2.4.2. Bypass Register 280
- C.2.5 TAP Controller 281
- C.2.5.2. Run-Test/Idle State 282
- C.2.5.3. Select-DR-Scan State 282
- C.2.5.4. Capture-DR State 282
- C.2.5.5. Shift-DR State 283
- C.2.5.6. Exit1-DR State 283
- C.2.5.7. Pause-DR State 283
- C.2.5.8. Exit2-DR State 283
- C.2.5.9. Update-DR State 284
- C.2.5.11. Capture-IR State 284
- C.2.5.12. Shift-IR State 284
- C.2.5.13. Exit1-IR State 285
- C.2.5.14. Pause-IR State 285
- C.2.5.15. Exit2-IR State 285
- C.2.5.16. Update-IR State 285
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