arch.example.tex

   1 \subsection{Framework}
   2 Systems built with support for \gls{mTask} are often following the same design
   3 pattern. First the devices are created --- with or without the interaction of
   4 the user --- and they are then connected. When all devices are registered, the
   5 \gls{mTask}-\glspl{Task} can be sent and \gls{iTasks}-\glspl{Task} can be
   6 started to monitor the output. When everything is finished, the devices are
   7 removed and the system is shut down.
   8
   9 \begin{lstlisting}[language=Clean,label={lst:framework},
  10         caption={\gls{mTask} framework for building applications}]
  11 w :: Task ()
  12 w =         makeDevice "dev1" (...) >>= connectDevice
  13         >>= \dev1->makeDevice "dev2" (...) >>= connectDevice
  14         >>= \dev2->...
  15         ...
  16         >>* [OnAction (Action "Shutdown") $ always
  17                 $   deleteDevice dev1 >>| deleteDevice dev2
  18                 >>| ...
  19                 >>| shutDown 0
  20         ]
  21 \end{lstlisting}
  22
  23 \subsection{Thermostat}
  24 The thermostat is a classic example program for showing interactions between
  25 peripherals. The following program shows a system containing two devices. The
  26 first device --- the sensor --- contains a temperature sensor that measures the
  27 room temperature. The second device --- the actor --- contains a heater,
  28 connected to the digital pin \CI{D5}. Moreover, this device contains a led to
  29 indicate whether the heater is on. The following code shows an implementation
  30 for this. The code fully uses the framework. Note that a little bit of type
  31 twiddling is required to fully us the result from the \gls{SDS}. This approach
  32 is still type safe due to the type safety of \CI{Dynamic}s.
  33
  34 \begin{lstlisting}[caption={Thermostat example}]
  35 thermos :: Task ()
  36 thermos =           makeDevice "nodeM" nodeMCU >>= connectDevice
  37         >>= \nod->      makeDevice "stm32" stm32   >>= connectDevice
  38         >>= \stm->      sendTaskToDevice "sensing" sensing (nod, OnInterval 1000)
  39         >>= \(st, [t])->sendTaskToDevice "acting" acting (stm, OnInterval 1000)
  40                         (\(BCValue s)->set (BCValue $ dynInt (dynamic s) > 0) (shareShare nod a))
  41         >>| treturn ()
  42 where
  43         dynInt :: Dynamic -> Int
  44         dynInt (a :: Int) = a
  45
  46         sensing = sds \x=0 In {main=
  47                         x =. analogRead A0 :. pub x
  48                 }
  49         acting = sds \cool=False In {main=
  50                         IF cool (ledOn LED1) (ledOff LED1) :.
  51                         digitalWrite D5 cool
  52                 }
  53         nodeMCU = TCP
  54 \end{lstlisting}
  55
  56 \subsection[Lifting mTasks to iTasks-Tasks]%
  57         {Lifting \gls{mTask}-\glspl{Task} to \gls{iTasks}-\glspl{Task}}
  58 If the user does not want to know where and when a \gls{mTask} is actually
  59 executed and is just interested in the results it can lift the \gls{mTask} to
  60 an \gls{iTasks}-\gls{Task}. The function is called with a name, \gls{mTask},
  61 device and interval specification and it will return a \gls{Task} that finishes
  62 if and only if the \gls{mTask} has returned.
  63
  64 \begin{lstlisting}[caption={Lifting \gls{mTask}-\glspl{Task} to \gls{iTasks}}]
  65 liftmTask :: String (Main (ByteCode () Stmt)) (MTaskDevice, MTaskInterval) -> Task [MTaskShare]
  66 liftmTask wta mTask c=:(dev, _)= sendTaskToDevice wta mTask c
  67         >>= \(t, shs)->wait "Waiting for mTask to return" (taskRemoved t) (deviceShare dev)
  68         >>| viewInformation "Done!" [] ()
  69         >>| treturn shs
  70 where
  71         taskRemoved t d = isNothing $ find (\t1->t1.ident==t.ident) d.deviceTasks
  72 \end{lstlisting}
  73
  74 The factorial function example from Chapter~\ref{chp:mtaskcont} can then be
  75 lifted to a real \gls{iTasks}-\gls{mTask} with the following code:
  76 \begin{lstlisting}[caption={Lifting the factorial \gls{Task} to \gls{iTasks}}]
  77 factorial :: MTaskDevice -> Task BCValue
  78 factorial dev = enterInformation "Factorial of ?" []
  79         >>= \fac->liftmTask "fact" (fact fac) (dev, OnInterval 100)
  80         @         fromJust o find (\x->x.humanName == "result")
  81         @         \s->s.MTaskShare.value
  82 where
  83         fact i = sds \y=i
  84                 In namedsds \x=(1 Named "result")
  85                 In {main = IF (y <=. lit 1)
  86                         ( pub x :. retrn                  )
  87                         ( x =. x *. y :.  y =. y -. lit 1 )}
  88 \end{lstlisting}
  89
  90 \subsection{Heartbeat \& Oxygen Saturation Sensor}
  91 As an example, the addition of a new sensor will be demonstrated. The heartbeat
  92 and oxygen saturation sensor add-on is a \textsc{PCB} the size of a fingernail
  93 with a red \gls{LED} and a light sensor on it. Moreover, it contains an
  94 \textsc{I2C} chip to communicate. The company producing the chip provides the
  95 programmer with example code for \gls{Arduino} and \textsc{mbed}. The sensor
  96 emits red light and measures the returning light intensity. The microcontroller
  97 hosting the device has to keep track of four seconds of samples to determine
  98 the heartbeat. In the \gls{mTask}-system, an abstraction is made. The current
  99 implementation runs on \textsc{mbed} supported devices.
 100 %TODO Adding peripheral is supposedly simple.