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.
   4
   5 \begin{lstlisting}[caption={Thermostat bytecode},language=c]
   6  1-2 : BCAnalogRead (Analog A0)
   7  3-6 : BCPush (Int 50)
   8  7   : BCGre
   9  8-9 : BCJmpF 17                   //Jump to else
  10 10-12: BCPush (Bool 1)
  11 13-14: BCDigitalWrite (Digital D0)
  12 15-16: BCJmp 21                    //Jump to endif
  13 17-19: BCPush (Bool 0)             //Else label
  14 20   : BCDigitalWrite (Digital D0)
  15 21   :                             //Endif label
  16 \end{lstlisting}
  17
  18 The factorial function can be expressed as an \gls{mTask}-\gls{Task} and uses
  19 the \CI{sds} and the \CI{return} functionality. Typically this \gls{Task} is
  20 called with the \CI{OnInterval} scheduling strategy and will calculate the
  21 factorial after which is will return. The following listings shows the actual
  22 \gls{mTask} and the generated messages followed by the actual bytecode in a
  23 readable form.
  24
  25 \begin{lstlisting}[caption={Factorial as an \gls{mTask}-\gls{Task}}]
  26 factorial :: Int -> Main (ByteCode () Stmt)
  27 factorial i = sds \y=i In
  28         namedsds \x=1 Named "result" In
  29         {main =
  30                 IF (y <=. lit 1) (
  31                         pub x :. retrn
  32                 ) (
  33                         x =. x *. y :. y =. y -. lit 1
  34                 )}
  35
  36 //Generating the actual messages with:
  37 Start = fst $ toMessages (OnInterval 500) (factorial 5) zero
  38
  39 //The output will be
  40 //[MTSds 2 (BCValue 5), MTSds 1 (BCValue 1), MTTask (OnInterval 500) ...]
  41 \end{lstlisting}
  42
  43 \begin{lstlisting}[label={lst:actualbc},%
  44         caption={The resulting bytecode for the factorial function},language=C]
  45  0-2 : BCSdsFetch 1
  46  3-6 : BCPush (Int 1)
  47  7   : BCLeq
  48  8-9 : BCJmpF 16                    //Jump to else
  49 10-12: BCSdsPublish 2 ("result")
  50 13   : BCReturn
  51 14-15: BCJmp 37                     //Jump to endif
  52 16-18: BCSdsFetch 2 ("result")      //Else label
  53 19-21: BCSdsFetch 1
  54 22   : BCMul
  55 23-25: BCSdsStore 2 ("result")
  56 26-28: BCSdsFetch 1
  57 29-32: BCPush (Int 1)
  58 33   : BCSub
  59 34-36: BCSdsStore 1
  60 37   :                               //Endif label
  61 \end{lstlisting}