Describing and Controlling Physical Processes using Java (Brainstorm)

1. Describing and Controlling Physical Processes using Java(Brainstorm) Wind Turbine Instrumentation Project

2. Goals • We need a language the can be used to: • Formally describe the input/output of a physical process • Formally describe a sensor that translates a physical quantity to a digital quantity. • Formally describe the control of a physical process. • Formally describe the interaction between different controls of a physical process.

3. Goals • The language should be able to describe constraints such as • Hard Real Time constraints • Soft Real Time constraints as a probability function. • Accuracy • Power consumption • Communication constraints (rate, delay) • Redundancy • Other parameters….

4. Goals • The language should be flexible enough so verification of the constraints should be possible.

5. Language Options • Invent a new language mixing up existing similar languages • Advantage: Easier to specify models and to write tools. • Disadvantage: No existing infrastructure. More difficult learn a new language. • Extend or annotate Java. • Advantage: Existing infrastructure and experience. Easier to adopt. • Disadvantage: More difficult to describe models. Tools more difficult to write to extract info. Too general and flexible to be verified for all constraints.

6. How Java could be extended • There are already keywords in Java that add constranits to the execution of a program: atomic: Restrict sthe execution of blocks, Volatile: Restricts the placement of variables • We could have new keywords like “restrict”

7. Example use of “restrict” while (true) { restrict (Time=1ms) { FFT fft1 = accelerometer1.read().fft(); FFT fft2 = accelerometer2.read().fft(); FFT fft3 = accelerometer3.read().fft(); if ( fft1.diff(fft2) > MAXFFTDIFF || fft1.diff(fft3) > MAXFFTDIFF ) { administrator.report(); } } // End of restrict } • The block is restricted to run under 1ms.

8. Comments • Read() calls may happen in parallel. We need a way to specify that parallelism. • RTJava may have already some keywords that do this. • The “restrict” keyword could be checked statically at compilation time but it is extremely difficult or at runtime that is more practical. • At runtime the “restrict” can be like an “assertion” that can report a problem. • We could add this “restrict as part of the language syntax or as a compatible addition of the language. • Example:

9. Using “Restrict” without Language extension while (true) { // !-- Restrict Time=1ms { FFT fft1 = accelerometer1.read().fft(); FFT fft2 = accelerometer2.read().fft(); FFT fft3 = accelerometer3.read().fft(); if ( fft1.diff(fft2) > MAXFFTDIFF || fft1.diff(fft3) > MAXFFTDIFF ) { administrator.report(); } // !-- } End of restrict } A preprocessor would extract the info in “//!—” and insert code for verification at runtime or to an static analyzer.