mtaskext.examples.tex

   1 As an example for the bytecode compilation the following listing shows the
   2 thermostat example given in Listing~\ref{lst:exmtask} compiled to bytecode.
   3 The left column indicates the position in the program memory. The \CI{endif}
   4 label is resolved to an address outside of the program space. This is not a
   5 problem since this is included in the stopping condition of the interpreter.
   6 When the program counter exceeds the length of the program, the task
   7 terminates.
   8
   9 \begin{lstlisting}[language=Clean,caption={Thermostat bytecode},language=c]
  10  0-1 : BCAnalogRead (Analog A0)
  11  2-5 : BCPush (Int 50)
  12  6   : BCGre
  13  7-8 : BCJmpF 17                   //Jump to else
  14  9-11: BCPush (Bool 1)
  15 12-13: BCDigitalWrite (Digital D0)
  16 14-15: BCJmp 21                    //Jump to endif
  17 16-18: BCPush (Bool 0)             //Else label
  18 19   : BCDigitalWrite (Digital D0)
  19 20   :                             //Endif label
  20 \end{lstlisting}
  21
  22 The factorial function can be expressed as an \gls{mTask}-\gls{Task} and uses
  23 the \CI{sds} and the \CI{return} functionality. Typically this \gls{Task} is
  24 called with the \CI{OnInterval} scheduling strategy and will calculate the
  25 factorial after which is will return. The following listings shows the actual
  26 \gls{mTask} and the generated messages followed by the actual bytecode in a
  27 readable form.
  28
  29 \begin{lstlisting}[language=Clean,caption={Factorial as an \gls{mTask}-\gls{Task}}]
  30 factorial :: Int -> Main (ByteCode () Stmt)
  31 factorial i = sds \y=i In
  32         namedsds \x=1 Named "result" In
  33         {main =
  34                 IF (y <=. lit 1) (
  35                         pub x :. retrn
  36                 ) (
  37                         x =. x *. y :. y =. y -. lit 1
  38                 )}
  39
  40 //Generating the actual messages with:
  41 Start = fst $ toMessages (OnInterval 500) (factorial 5) zero
  42
  43 //The output will be
  44 //[MTSds 2 (BCValue 5), MTSds 1 (BCValue 1), MTTask (OnInterval 500) ...]
  45 \end{lstlisting}
  46
  47 \begin{lstlisting}[language=Clean,label={lst:actualbc},%
  48         caption={The resulting bytecode for the factorial function},language=C]
  49  0-2 : BCSdsFetch 1
  50  3-6 : BCPush (Int 1)
  51  7   : BCLeq
  52  8-9 : BCJmpF 16                    //Jump to else
  53 10-12: BCSdsPublish 2 ("result")
  54 13   : BCReturn
  55 14-15: BCJmp 37                     //Jump to endif
  56 16-18: BCSdsFetch 2 ("result")      //Else label
  57 19-21: BCSdsFetch 1
  58 22   : BCMul
  59 23-25: BCSdsStore 2 ("result")
  60 26-28: BCSdsFetch 1
  61 29-32: BCPush (Int 1)
  62 33   : BCSub
  63 34-36: BCSdsStore 1
  64 37   :                               //Endif label
  65 \end{lstlisting}