The Esterel v5 21 System Manual - Courses

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18 CHAPTER 2. USING THE ESTEREL COMPILER Then, the sscblif processor replaces sscc. To extract the control of a general Esterel program, one must pass the option -soft to sscblif. This is done as follows: esterel -Lblif:-soft bigprogram.strl The Esterel v5 21 compiler is open, and other code generators may be added to it. Typing option -Lbar will call the sscbar code generator. 2.3.2 Unsorted Circuit Code Generation Object C code is directly generated from the sc unsorted circuit code when option -I is used, as in esterel -I -simul main.strl aux.strl -B foo The processor chain is strlic, iclc, lcsc, and scc. Unsorted circuit code has major advantages but also some drawbacks. Let us start with the advantages. First, the -I option makes it possible to compile cyclic programs that contain instantaneous cyclic dependencies between signals, such as the Cyclic program above. Compiling is always very fast. However, cyclic programs may or may not have a meaning, according to the constructive semantics of Esterel described in [1]. With option -I, all Esterel programs generate C code, be them meaningful or not. At run-time, for each input event, the C code performs a fast interpretation of the circuit that succeeds and produces the right output and state change if and only if the program-input pair is meaningful, i.e. constructive in the sense of [1]. If the program-input pair is non-constructive, execution returns an error code that must be checked by the caller. Examples of constructive and non-constructive cyclic programs are given in [1]. Second, the -I option is especially useful for simulation. Running esterel -I -simul foo.strl and invoking the xes simulator as before, one can simulate any Esterel program. Constructiveness errors will provoke simulation errors and an explanation of the error will be given directly on the source code using the xes source code debugging interface, see Section 5.4.8. Furthermore, symbolic debugging is enhanced since the exact control path followed during the transition is shown on the source code using a green background. Therefore, we strongly recommend to use option -I when running xes (try it on the wristwatch example).
2.3. CONTROLLING CODE GENERATION 19 The drawback is of course that causality errors are not reported at compile-time when the -I option is used, which may be misleading. Fortunately, the Esterel v5 21 compiler provides a way to check that a program is constructive. Just type esterel -W -Icheck foo.strl This calls the aforementioned sccausal processor, performs the full constructiveness analysis, but does not generate code. If option -Icheck succeeds, the generated code will never encounter a causality error and it is safe to embed it. Other properties such as single emission of single signals are also checked on the way. If errors are found during the check, they are reported graphically using a variant of the xes processor. WARNING: Option -Icheck should always be used before embedding code generated with option -I. Since this option also checks single emission of single signals, which is not checked by default, the option should also be used before embedding any Esterel generated code. 2.3.3 Automaton Code Generation A third possibility for software code generation is to generate an automatonbased code. The main advantage is speed: reactions using automata are usually faster than reactions using sorted or unsorted circuit code. The main drawback is size: in the worst case, the automaton table can be exponentially bigger than the source code, while the circuit’s size is most often linear and worst-case square. Automata are usually preferred for small applications (man-machine interface drivers, communication protocols, etc). Try both automata and circuits for a given application, and choose the best. There is no general choice rule. Automaton code generation can be done in three ways. First, one can use the -A option: esterel -A [-simul] foo.strl The processor chain is strlic, iclc, lcsc, scssc, sscoc, and occ. Second, one can use the -A option in conjunction with the -causal option: esterel -causal -A [-simul] foo.strl Then scssc is replaced by sccausal. This process generates an automaton from any constructive Esterel program, but it can be quite expensive. Third, one can use the former Esterel v3 technology:
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Page 8 and 9: 2 PREFACE feedback. WARNING: Chapte
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100 CHAPTER 7. SIMULATION EXAMPLES
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112 CHAPTER 8. CONSTRUCTIVE CYCLIC
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Index !, see csimul ?, see csimul #
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124 INDEX ?, 85 combined signal, 88
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126 INDEX lc, 12, 13, 27 -lc, 15, 2
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128 INDEX scc, 13, 18 sccausal, 12,
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130 INDEX high/low inputs, 67, 72 i
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