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Design and Verification of Adaptive Cache Coherence Protocols ...

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M-engine Rule <strong>of</strong> <strong>Cache</strong>t Deriving Imperative & Directive Rules<br />

VM1 IM1<br />

VM2 IM2<br />

VM3 Send-DownReqwb<br />

VM4 Send-DownReqmw<br />

VM5 Send-DownReqwb<br />

MM1 IM3<br />

MM2<br />

MM3 IM4<br />

MM4 IM4<br />

MM5 Send-DownReqmw<br />

MM6<br />

MM7<br />

MM8 IM5<br />

MM9 IM5<br />

MM10 IM5<br />

MM11 IM6 + Send-DownReqwb<br />

MM12 IM6<br />

MM13 IM7 + Send-DownReqwb<br />

MM14 IM7<br />

MM15 IM8 + Send-DownReqmw + Send-DownReqwb<br />

MM16 IM8 + Send-DownReqwb<br />

MM17 IM8<br />

MM18 IM9<br />

MM19 IM9<br />

MM20 IM9<br />

MM21 IM10<br />

MM22 IM10<br />

MM23 IM11<br />

MM24 IM11<br />

MM25 IM11<br />

MM26 IM12<br />

MM27 IM12<br />

MM28 IM12<br />

MM29 IM13<br />

MM30 IM13<br />

MM31 IM13<br />

MM32 IM14<br />

MM33 IM15<br />

MM34<br />

Figure 7.16: Derivation <strong>of</strong> Memory Engine Rules <strong>of</strong> <strong>Cache</strong>t<br />

Figure 7.18 gives the basic rules used in the simulation <strong>of</strong> each composite rule.<br />

The <strong>Cache</strong>t Protocol Appendix A gives the speci cation <strong>of</strong> the complete <strong>Cache</strong>t protocol,<br />

which contains the basic rules de ned in Figures 7.11, 7.12 <strong>and</strong> 7.13, <strong>and</strong> the composite rules<br />

de ned in Figure 7.17. The <strong>Cache</strong>t protocol is an adaptive cache coherence protocol, although<br />

for pedagogic reason it has been been presented as an integration <strong>of</strong> several micro-protocols.<br />

One can also think <strong>Cache</strong>t as a family <strong>of</strong> protocols because <strong>of</strong> the presence <strong>of</strong> voluntary rules<br />

that can be invoked without the execution <strong>of</strong> an instruction or the receipt <strong>of</strong> a message. The<br />

existence <strong>of</strong> voluntary rules provides enormous extensibility in the sense that various heuristic<br />

messages <strong>and</strong> states can be employed to invoke these rules.<br />

As an example <strong>of</strong> how the adaptivity can be exploited, consider a DSM system with limited<br />

directory space. When the memory receives a cache request, it can respond under Base or WP.<br />

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