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Synchronous Reactive Communication: Generalization , Implementation, and Optimization

Synchronous Reactive Communication: Generalization , Implementation, and Optimization. Guoqiang Gerald Wang PhD Candidate Committee in charge: Prof . Alberto Sangiovanni-Vincentelli , Chair Prof. Robert K. Brayton Prof. Zuojun Shen December 9, 2008. Outline.

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Synchronous Reactive Communication: Generalization , Implementation, and Optimization

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  1. Synchronous Reactive Communication: Generalization, Implementation, and Optimization GuoqiangGerald Wang PhD Candidate Committee in charge: Prof. Alberto Sangiovanni-Vincentelli, Chair Prof. Robert K. Brayton Prof. ZuojunShen December 9, 2008

  2. Outline • Background and previous work • Methodology and implementation framework • SR semantics preserving communication protocols • Protocol implementation under OSEK OS standard • Memory optimization under timing constraints • Automatic code generation • Conclusions • Background and previous work • Methodology and implementation framework • SR semantics preserving communication protocols • Protocol implementation under OSEK OS standard • Memory optimization under timing constraints • Automatic code generation • Conclusions

  3. System-Level Design • On the edge of a revolution in the way electronic products are designed • Increasing design complexity • High product quality • Stronger market pressure • System-level design is the key to success • Start with the highest possible level of abstraction (e.g. control algorithm) • Establish properties at the right level • Use formal models • Leverage multiple scientific disciplines Background

  4. Models of Computation • Process Networks (PN) • Undecidable: deadlocks and buffer boundedness • Synchronous Reactive (SR) • WRT model time • computation doesn’t take time • All actors execute simultaneously and instantaneously • Has strong formal properties: decidable termination & boundedness • Good for specifying periodic real-time tasks • Discrete Event (DE) • Signals are time-stamped events • Events are processed in chronological order • Good for modeling and design of time-based systems • Dataflow process networks • Dataflow processes are Kahn processes composed of atomic firings Background

  5. Implementation Tools • Academia: • MetroPolis (ASV, UCB) • Meta model • Communication refinement • Ptolemy (E. Lee, UCB) • Started with static dataflow for DSP • Mixed model verification • Industry: • LabVIEW • Statically schedulable dataflow (Synchronous dataflow) • Simulink • Synchronous reactive Support multiple models of computation Background

  6. Model-Based Design • An instance of system-level design • Very popular • Tool support • Design time simulation/verification • Short development cycle • Predictable performance • Flexibility of new design evaluation • Design reuse • The rest of the presentation • Synchronous reactive model-based design Background

  7. SR Semantics Donald, I am sending $5 and an apple. Get $5 and an apple. Thanks, Mickey! My turn to run! Now I am done. Time for me to run I finished. $5 prioritym > priorityd periodm < periodd Simulation time t0 t1 During simulation, writer and reader respond instantaneously (computation takes zero time) Background

  8. base rate time 0 2 8 16 Task 1 time 0 2 8 16 Task 2 time 0 2 8 16 Implementation Options of Multi-Rate systems • Single-task option • Multiple-task option unschedulable -> 6.1 Background

  9. Model Implementation (Case I) I need to yield to Mickey. Donald, I send $1 and a banana this time. Now, I can start. Time for me to run again. Now I am done. I can resume. My turn to run. But need to wait. Start receiving. Now I am done. Get $1 and a banana. Donald, I am sending $5 and an apple. $1 $5 I finished. Time for me to run real time prioritym> priorityd periodm< periodd t0 t1 t2 t3 t4 t5 Communication is not atomic Uni-processor and priority-based preemptive scheduling Background

  10. Model Implementation (Case II) Start receiving. Got $5! Not finished yet. Have to yield. Donald, I send $1 and a banana this time. Now, I can start. Time for me to run again. Now I am done. My turn to run. But need to wait. Resume receiving. Now I am done. A banana. Wow, $5 and a banana!! Donald, I am sending $5 and an apple. $1 $5 I finished. Time for me to run real time t0 t1 t2 t3 t4 t5 Background

  11. What Is the Difference $5 SR Semantics simulation time $5 $5 $1 data determinism problem real time Case I $1 first second $1 $5 data integrity problem Case II real time $5 Background

  12. Current Approach Limitations and Solutions • Rate transition buffering scheme from The MathWorks • Limitations • One to one communication • Double buffering scheme • No memory optimization • For periodic communicating tasks: • Periods must be harmonic • Tasks must be activated with the same phase • Solutions • One to many communication • Dynamic buffering and temporal currency control protocols • For periodic communicating tasks: • Raise the implementation up to the kernel level • Furthermore, • Generalization with support of arbitrary link delay and multiple activations per task • Memory optimization through automatic protocol selection Background

  13. Outline • Background and previous work • Methodology and implementation framework • SR semantics preserving communication protocols • Protocol implementation under OSEK OS standard • Memory optimization under timing constraints • Automatic code generation • Conclusions

  14. Methodology • Platform-based design • Automatic generation of • application tasks • communication protocol implementation • Automatic configuration of RTOS procedures and data structures • Flexibility of choice of RTOS API standard Methodology

  15. Meet-in-the-Middle Approach Application Functional Model • Application domain • Time-critical applications • Modeled as SR tasks • Platform • Task/resource model platform • Task’s characteristics and interaction • RTOS platform • Priority-based scheduling policies • Inter-task comm. protocols • lock-based, lock-free, wait-free • Middle meeting point • RTOS API • OSEK/VDX, POSIX, μITRON • Execution architecture • Uni-processor • Priority-based preemptive scheduling Task Model; Communication Resource Model Mapping RTOS API Export Scheduling Policy: FP, DP; Communication Resource Management Policy Execution Architecture Methodology

  16. Design Flow Specification of SR models Model-based design tool Application configuration files (OIL) C code OSEK OS Kernel OSEK COM System Generator (SG) Files produced by SG User’s source code C code C code compiler linker Object libraries Executable file Methodology

  17. τi · · · · NIP NOP · · Task Model τi • Parameter characterization • Priority: • Period: • Activation time: • Start time: • Worst-case computation time: • Finish time: • Worst-case response time: • Relative deadline: time Methodology

  18. Outline • Background and previous work • Methodology and implementation framework • SR semantics preserving communication protocols • Protocol implementation under OSEK OS standard • Memory optimization under timing constraints • Automatic Code Generation • Conclusions

  19. SR Semantics with Link Delay j ri time in out w ··· time SR Protocols

  20. One to Many Communication: Single-Writer Multiple-Reader • General case: and • Special case: and HPR: ··· ··· Link delay: design parameter ··· LPR: ··· SR Protocols

  21. SR Semantics Preserving Communication mechanisms • Wait-free scheme • Buffer sizing mechanisms • Spatially-out-of-order writes • Spatially-in-order writes • Buffer indexing protocols • Dynamic Buffering Protocol (DBP) • Temporal Concurrency Control Protocol (TCCP) SR Protocols

  22. LPR HPR Spatially-out-of-Order Writes • Buffer sizing: Buf[] Read[] prev 0 2 0 0 5 5 1 cur 1 1 0 1 2 2 3 4 3 3 4 4 2 5 2 5 2 6 SR Protocols

  23. Spatially-in-Order Writes • Offset • Buffer sizing I finished. activated Unit delay buffer index writer instance SR Protocols

  24. How to Guarantee SR Semantics • Handle communication at two levels • Buffer indices defined at activation time by kernel • Data reading/writing at execution time by application tasks SR Protocols

  25. The Protocols FreeHd 2 3 0 4 1 1 2 1 3 5 4 -1 5 UseFreeL[6] SR Protocols

  26. Outline • Background and previous work • Methodology and implementation framework • SR semantics preserving communication protocols • Protocol implementation under OSEK OS standard • Memory optimization under timing constraints • Automatic code generation • Conclusions

  27. OSEK/VDX • A series of standards particularly for automotive designs • Basic and extended tasks • Four Conformance Classes • BCC1, BCC2, ECC1, ECC2 • Portability • Minimum requirement of CC • Kernel services: • Task management, alarm, hook mechanism • OIL • Modular configuration for system generation OSEK Implementation

  28. DispHd size tick TickL[LCMR] DispT[TSize] An OSEK/VDX Implementation • Portable implementation • BCC1 • Minimum Requirement • Only one alarm • Task dispatcher • GCD of rates OSEK Implementation

  29. Implementation (cont) • Application task OSEK Implementation

  30. Comparison of CTDBP & TCCP OSEK Implementation

  31. Outline • Background and previous work • Methodology and implementation framework • SR semantics preserving communication protocols • Protocol implementation under OSEK OS standard • Memory optimization under timing constraints • Automatic code generation • Conclusions

  32. Mathematical Formulation • Fixed given priority • Parameters: • Variables: Buffer sizing mechanisms: Optimization

  33. Complete Formulation Reformulate: MILP Schedulability constraint Buffer size Lifetime WCRT Protocol flag Partial cost of dispatcher Cost of context switches Optimization

  34. Experimental Setup • Performance evaluation environment • PIC18F452 • Performance up to 10 MIPS • ePICos18 • Multi-task, preemptive, O(1) kernel scheduler • OSEK compliant • Task graphs generated by TGFF • 809 systems (158 unschedulable) • On average, 12 tasks/graph; execution time: 6•104ICs; task period: 106ICs • ≤ 4(8) writers(readers)/task; ≤ 2-unit delay; Optimization

  35. Experimental Results 4.8% 14% 24% Optimization

  36. Outline • Background and previous work • Methodology and implementation framework • SR semantics preserving communication protocols • Protocol implementation under OSEK OS standard • Memory optimization under timing constraints • Automatic code generation • Conclusions

  37. Real-Time Workshop • Simulink system functions (S-Functions) • Extend capability of Simulink environment • Coded in C or MATLAB • Target Language Compiler (TLC) • From graphical model to intermediate form • Eventually into target specific code • RTW Embedded Coder (E-Coder) • Framework for development of embedded software Code Generation

  38. SR Implementation Library Code Generation

  39. Example of DyB Given: sampling rates, buffer initial value (8) Period of task dispatcher? How many buffer slots? How many tasks? GCD(2,3,5) = 1 NLPR + 1 + 1 = 3 5 Code Generation

  40. Simulation/Emulation Results RTW MPLAB(PIC18F452) + ePICos18 Period = 3 Period = 5 Period = 2 Code Generation

  41. Conclusions • Generalized theory on SR semantics preserving communication • Implemented protocols with portability consideration under the OSEK OS standard • Optimized memory and supported a wider range of applications under timing constraints with automatic protocol selection • Supported automatic code generation for SR communication protocols

  42. Thank you

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