MIPS R10000 Microprocessor User's Manual - SGI TechPubs Library

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24 Chapter 1. bne r1, r0, label ----- ----- ----- ----movn ra, r0, r1 # test to see if r1 != 0; if r1 != 0 then branch # is mispredicted; move safe address (r0) # into ra ld ----- ---r4, 0 (ra) # Without the previous movn, this lld # could create damaging read. label: ----- ----- ----- In the above example, without the MOVN the read to the address in register ra could be speculatively executed and later aborted. It is possible that this load could be premature and thus damaging. The MOVN guarantees that if there is a misprediction (r1 is not equal to 0) ra will be loaded with an address to which a read will not be damaging. 6. The following is similar to the conditional-move example given above, in that it protects speculation only for a single branch, but in some instances it may be more efficient than either the conditional move or the cache barrier workarounds. This workaround uses the fact that branch-likely instructions are always predicted as taken by the R10000. Thus, any incorrect speculation by the R10000 on a branch-likely always occurs on a taken path. Sample code is: beql rx, r1, label nop sw r2, 0x0(r1) label: ----- ----- The store to r1 will never be to an address referred to by the content of rx, because the store will never be executed speculatively. Thus, the address referred to by the content of rx is protected from any spurious write-backs. Version 2.0 of January 29, 1997 MIPS R10000 Microprocessor User's Manual
Introduction to the R10000 Processor 25 Nonblocking Caches This workaround is most useful when the branch is often taken, or when there are few instructions in the protected block that are not memory operations. Note that no instructions in a block following a branch-likely will be initiated by speculation on that branch; however, in the case of a serial instruction workaround, only memory operations are prevented from speculative initiation. In the case of the conditional-move workaround, speculative initiation of all instructions continues unimpeded. Also, similar to the conditional-move workaround, this workaround only protects fall-through blocks from speculation on the immediately preceding branch. Other mechanisms must be used to ensure that no other branches speculate into the protected block. However, if a block that dominates † the fall-through block can be shown to be protected, this may be sufficient. Thus, if block (a) dominates block (b), and block (b) is the fall-through block shown above, and block (a) is the immediately previous block in the program (i.e., only the single conditional branch that is being replaced intervenes between (a) and (b)), then ensuring that (a) is protected by serial instruction means a branch-likely can safely be used as protection for (b). As processor speed increases, the processor’s data latency and bandwidth requirements rise more rapidly than the latency and bandwidth of cost-effective main memory systems. The memory hierarchy of the R10000 processor tries to minimize this effect by using large set-associative caches and higher bandwidth cache refills to reduce the cost of loads, stores, and instruction fetches. Unlike the R4400, the R10000 processor does not stall on data cache misses, instead defers execution of any dependent instructions until the data has been returned and continues to execute independent instructions (including other memory operations that may miss in the cache). Although the R10000 allows a number of outstanding primary and secondary cache misses, compilers should organize code and data to reduce cache misses. When cache misses are inevitable, the data reference should be scheduled as early as possible so that the data can be fetched in parallel with other unrelated operations. As a further antidote to cache miss stalls, the R10000 processor supports prefetch instructions, which serve as hints to the processor to move data from memory into the secondary and primary caches when possible. Because prefetches do not cause dependency stalls or memory management exceptions, they can be scheduled as soon as the data address can be computed, without affecting exception semantics. Indiscriminate use of prefetch instructions can slow program execution because of the instruction-issue overhead, but selective use of prefetches based on compiler miss prediction can yield significant performance improvement for dense matrix computations. † In compiler parlance, block (a) dominates block (b) if and only if every time block (b) is executed, block (a) is executed first. Note that block (a) does not have to immediately precede block (b) in execution order; some other block may intervene. MIPS R10000 Microprocessor User's Manual Version 2.0 of January 29, 1997
Page 1 and 2:
MIPS R10000 Microprocessor User’s
Page 3 and 4: Acknowledgments This book represent
Page 5 and 6: About This Manual Glossary Stylisti
Page 7 and 8: Table of Contents vii Contents Ackn
Page 9 and 10: Table of Contents ix Superscalar In
Page 11 and 12: Table of Contents xi 3 Interface Si
Page 13 and 14: Table of Contents xiii 5 Secondary
Page 15 and 16: Table of Contents xv SysAD[63:0] Ad
Page 17 and 18: Table of Contents xvii 7 Clock Sign
Page 19 and 20: Table of Contents xix 9 Error Prote
Page 21 and 22: Table of Contents xxi 11 JTAG Inter
Page 23 and 24: Table of Contents xxiii 13 Packagin
Page 25 and 26: Table of Contents xxv Branch on Cop
Page 27 and 28: Table of Contents xxvii 16 Memory M
Page 29 and 30: Table of Contents xxix 18 A Cache T
Page 31 and 32: 1. Introduction to the R10000 Proce
Page 33 and 34: Introduction to the R10000 Processo
Page 53: Introduction to the R10000 Processo
Page 63 and 64: 2. System Configurations The R10000
Page 65 and 66: System Configurations 35 2.2 Multip
Page 67 and 68: 3. Interface Signal Descriptions Th
Page 69 and 70: Interface Signal Descriptions 39 3.
Page 75 and 76: 4. Cache Organization and Coherency
Page 77 and 78: Cache Organization and Coherency 47
Page 89 and 90: 5. Secondary Cache Interface The pr
Page 91 and 92: Secondary Cache Interface 61 5.2 Se
Page 93 and 94: Secondary Cache Interface 63 Indexi
Page 95 and 96: Secondary Cache Interface 65 Errata
Page 97 and 98: Secondary Cache Interface 67 SCTag(
Page 99 and 100: Secondary Cache Interface 69 4-Word
Page 101 and 102: Secondary Cache Interface 71 16 or
Page 103 and 104: Secondary Cache Interface 73 5.7 Wr
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Secondary Cache Interface 75 8-Word
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Secondary Cache Interface 77 Tag Wr
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6. System Interface Operations The
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System Interface Operations 81 6.4
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System Interface Operations 85 Mult
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System Interface Operations 87 Exte
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System Interface Operations 91 Outg
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System Interface Operations 97 Duri
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System Interface Operations 99 Erra
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System Interface Operations 101 Cyc
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System Interface Operations 103 Sys
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System Interface Operations 111 Mul
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System Interface Operations 113 Err
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System Interface Operations 115 Pro
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System Interface Operations 127 Ext
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System Interface Operations 143 Coh
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System Interface Operations 147 The
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System Interface Operations 149 In
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7. Clock Signals The R10000 process
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Clock Signals 157 7.2 Secondary Cac
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8. Initialization This section desc
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Initialization 161 Errata Vcc VccQ[
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Initialization 163 8.4 Soft Reset S
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Initialization 165 Table 8-1 (cont.
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9. Error Protection and Handling Th
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Error Protection and Handling 169 9
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Error Protection and Handling 177 D
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Error Protection and Handling 179 T
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Error Protection and Handling 181 E
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Error Protection and Handling 183 W
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Error Protection and Handling 185 P
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10. CACHE Instructions This chapter
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CACHE Instructions 189 TLB Refill a
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CACHE Instructions 191 Op Field Enc
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CACHE Instructions 193 10.4 Index W
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CACHE Instructions 195 10.7 Index L
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CACHE Instructions 197 10.11 Hit In
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CACHE Instructions 199 10.15 Hit Wr
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CACHE Instructions 201 10.17 Index
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11. JTAG Interface Operation Errata
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JTAG Interface Operation 205 11.2 I
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JTAG Interface Operation 207 ‡ Wi
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12. Electrical Specifications This
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Electrical Specifications 211 DCOk
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Electrical Specifications 213 Unuse
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Electrical Specifications 215 12.2
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Electrical Specifications 217 12.3
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13. Packaging The R10000 microproce
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Packaging 221 Electrical Characteri
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Packaging 223 Figure 13-1 R10000 59
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Packaging 225 Table 13-3 (cont.) Si
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Packaging 231 Figure 13-3 599LGA PW
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Packaging 233 Figure 13-5 599LGA Bo
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14. Coprocessor 0 This chapter desc
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Coprocessor 0 237 14.1 Index Regist
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Coprocessor 0 239 14.3 EntryLo0 (2)
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Coprocessor 0 241 14.4 Context (4)
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Coprocessor 0 243 14.6 Wired Regist
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Coprocessor 0 245 14.9 EntryHi Regi
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Coprocessor 0 247 CU2 CU2 CU1 CU1 C
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Coprocessor 0 249 Diagnostic Status
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Coprocessor 0 251 Coprocessor Acces
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Coprocessor 0 253 Table 14-13 Cause
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Coprocessor 0 255 14.13 Processor R
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Coprocessor 0 257 14.15 Load Linked
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Coprocessor 0 259 14.17 XContext Re
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Coprocessor 0 261 14.19 Diagnostic
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Coprocessor 0 263 Errata There are
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Coprocessor 0 265 Errata Errata The
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Coprocessor 0 267 Event 1 for Count
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Coprocessor 0 269 Event 6 for Count
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Coprocessor 0 271 Event 14 for Coun
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Coprocessor 0 273 14.21 ECC Registe
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Coprocessor 0 275 CacheErr Register
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Coprocessor 0 277 CacheErr Register
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Coprocessor 0 279 Errata Primary In
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Coprocessor 0 281 Errata Errata Sec
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Coprocessor 0 283 Primary Data Cach
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Coprocessor 0 285 14.25 CP0 Instruc
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Coprocessor 0 287 14.27 CACHE Instr
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Coprocessor 0 289 Cache CACHE (cont
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Coprocessor 0 291 14.29 DMTC0 Instr
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Coprocessor 0 293 14.31 MFC0 Instru
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Coprocessor 0 295 MTPS 31 Format: M
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Coprocessor 0 297 14.34 TLBP Instru
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Coprocessor 0 299 14.36 TLBWI Instr
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15. Floating-Point Unit This sectio
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Floating-Point Unit 303 15.2 Floati
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Floating-Point Unit 305 Load and St
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Floating-Point Unit 307 63 63 Doubl
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Floating-Point Unit 309 Floating-Po
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Floating-Point Unit 311 Loading the
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Floating-Point Unit 313 Moves and C
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16. Memory Management This section
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Memory Management 317 Addressing Mo
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Memory Management 319 32-bit User M
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Memory Management 321 32-bit Superv
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Memory Management 323 32-bit Kernel
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Memory Management 325 0X BFFFFFFF 0
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Memory Management 327 64-bit Virtua
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Memory Management 329 Using the TLB
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17. CPU Exceptions This chapter des
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CPU Exceptions 333 17.3 TLB Refill
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CPU Exceptions 335 Priority of Exce
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CPU Exceptions 337 Soft † Reset E
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CPU Exceptions 339 NMI Exception Ca
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CPU Exceptions 341 TLB Exceptions T
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CPU Exceptions 343 TLB Invalid Exce
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CPU Exceptions 345 Cache Error Exce
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CPU Exceptions 347 Integer Overflow
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CPU Exceptions 349 System Call Exce
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CPU Exceptions 351 Reserved Instruc
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CPU Exceptions 353 Floating-Point E
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CPU Exceptions 355 Interrupt Except
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CPU Exceptions 357 17.5 COP0 Instru
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18. Cache Test Mode The R10000 proc
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Cache Test Mode 361 18.3 Entering C
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Cache Test Mode 363 18.5 SysAD(63:0
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Cache Test Mode 365 Auto-Increment
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Cache Test Mode 367 Auto-Increment
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A. Glossary The following terms are
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A.6 Dynamic Scheduling The R10000 p
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A.11 Nonblocking Loads and Stores M
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A.13 Logical and Physical Registers
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Index I-1 Index Numerics 16-word, c
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Index I-3 uncached accelerated, des
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Index I-5 branch on CP0 instruction
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Index I-7 F fetch pipeline 6, 17 fe
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Index I-9 TLBWR 285, 300 unsupporte
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Index I-11 NMI see also nonmaskable
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Index I-13 CP0 (description of) 235
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Index I-15 SysAD[20:16] interrupt r
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Index I-17 SysWrRdy, signal 41, 118
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