arch.example.tex

   1 \subsection{Framework}
   2 Systems built with support for \gls{mTask} often follow 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 an
  29 \gls{LED} to indicate whether the heater is on. The following code shows an
  30 implementation for this. The code makes use of all the aspects of the
  31 framework. Note that a little bit of type twiddling is required to fully use
  32 the result from the \gls{SDS}. This approach is still type safe due to the type
  33 safety of \CI{Dynamic}s.
  34
  35 \begin{lstlisting}[language=Clean,caption={Thermostat example}]
  36 thermos :: Task ()
  37 thermos =           makeDevice "nodeM" nodeMCU >>= connectDevice
  38         >>= \nod->      makeDevice "stm32" stm32   >>= connectDevice
  39         >>= \stm->      sendTaskToDevice "sensing" sensing (nod, OnInterval 1000)
  40         >>= \(st, [t])->sendTaskToDevice "acting" acting (stm, OnInterval 1000)
  41                         (\(BCValue s)->set (BCValue $ dynInt (dynamic s) > 0) (shareShare nod a))
  42         >>* [OnAction (Action "Shutdown") $ always $ deleteDevice nod >>| deleteDevice stm >>| shutDown 0]
  43 where
  44         dynInt :: Dynamic -> Int
  45         dynInt (a :: Int) = a
  46
  47         sensing = sds \x=0 In {main=
  48                         x =. analogRead A0 :. pub x
  49                 }
  50         acting = sds \cool=False In {main=
  51                         IF cool (ledOn LED1) (ledOff LED1) :.
  52                         digitalWrite D5 cool
  53                 }
  54         nodeMCU = TCP
  55 \end{lstlisting}
  56
  57 \subsection[Lifting mTasks to iTasks-Tasks]%
  58         {Lifting \gls{mTask}-\glspl{Task} to \gls{iTasks}-\glspl{Task}}
  59 If the user does not want to know where and when an \gls{mTask} is actually
  60 executed and is just interested in the results, it can lift the \gls{mTask} to
  61 an \gls{iTasks}-\gls{Task}. The function is called with a name, \gls{mTask},
  62 device and interval specification and it will return a \gls{Task} that finishes
  63 if and only if the \gls{mTask} has returned.
  64
  65 \begin{lstlisting}[language=Clean,caption={Lifting \gls{mTask}-\glspl{Task} to \gls{iTasks}}]
  66 liftmTask :: String (Main (ByteCode () Stmt)) (MTaskDevice, MTaskInterval) -> Task [MTaskShare]
  67 liftmTask wta mTask c=:(dev, _)= sendTaskToDevice wta mTask c
  68         >>= \(t, shs)->wait "Waiting for mTask to return" (taskRemoved t) (deviceShare dev)
  69         >>| viewInformation "Done!" [] ()
  70         >>| treturn shs
  71 where
  72         taskRemoved t d = isNothing $ find (\t1->t1.ident==t.ident) d.deviceTasks
  73 \end{lstlisting}
  74
  75 The factorial function example from Chapter~\ref{chp:mtaskcont} can then be
  76 lifted to a real \gls{iTasks}-\gls{Task} with the following code:
  77 \begin{lstlisting}[language=Clean,caption={Lifting the factorial \gls{Task} to \gls{iTasks}}]
  78 factorial :: MTaskDevice -> Task BCValue
  79 factorial dev = enterInformation "Factorial of ?" []
  80         >>= \fac->liftmTask "fact" (fact fac) (dev, OnInterval 100)
  81         @         fromJust o find (\x->x.humanName == "result")
  82         @         \s->s.MTaskShare.value
  83 where
  84         fact i = sds \y=i
  85                 In namedsds \x=(1 Named "result")
  86                 In {main = IF (y <=. lit 1)
  87                         ( pub x :. retrn                  )
  88                         ( x =. x *. y :.  y =. y -. lit 1 )}
  89 \end{lstlisting}
  90
  91 \subsection{Heartbeat \& Oxygen Saturation Sensor}
  92 As an example, the addition of a new sensor will be demonstrated. The heartbeat
  93 and oxygen saturation sensor add-on is a \textsc{PCB} the size of a fingernail
  94 with a red \gls{LED} and a light sensor on it. Moreover, it contains an
  95 \textsc{I2C} chip to communicate. The company producing the chip provides the
  96 programmer with example code for \gls{Arduino} and \gls{mbed}. The sensor
  97 emits red light and measures the intensity of the light returned. The
  98 microcontroller hosting the device has to keep track of four seconds of samples
  99 to determine the heartbeat. In the \gls{mTask}-system, an abstraction is made.
 100 The current implementation runs on \gls{mbed} supported devices.
 101
 102 \subsubsection{\gls{mTask} Classes}
 103 First, a class has to be devised to store the functionality of the sensor. The
 104 heartbeat sensor updates four values continuously, namely the heartbeat, the
 105 oxygen saturation and the validity of the two. The real value and the validity
 106 are combined in an \gls{ADT} and functions are added for both of them in the
 107 new \CI{hb} class. The values are combined in such a way that they fit in a 16
 108 bit integer with the last bit representing the validity of the reading. The
 109 introduced datatype housing the values should implement the \CI{mTaskType}
 110 classes. The definition is as follows:
 111
 112 \begin{lstlisting}[language=Clean,%
 113         caption={The \texttt{hb} class and class implementations}]
 114 :: Heartbeat = HB Int Bool
 115 :: SP02      = SP02 Int Bool
 116
 117 instance toByteCode Heartbeat
 118         where toByteCode (HB i b) = "h" +++ (to16bit $ (i << 1) bitand (if b 1 0))
 119 instance toByteCode SP02 where ...
 120
 121 instance fromByteCode Heartbeat
 122         where fromByteCode s = let i = fromByteCode s //The Int from bytecode
 123                 in HB (i >> 1) (i bitand 1 > 0)
 124 instance fromByteCode SP02 where ...
 125
 126 derive class iTask Heartbeat, SP02
 127
 128 class hb v where
 129         getHb     :: (v Heartbeat Expr)
 130         getSp02   :: (v SP02 Expr)
 131 \end{lstlisting}
 132
 133 \subsubsection{Bytecode Implementation}
 134 The class is available now, and the implementation can be created. The
 135 implementation is trivial since the functionality is limited to retrieving
 136 single values and no assignment is possible. The following code shows the
 137 implementation. Dedicated bytecode instructions have been added to support the
 138 functionality.
 139
 140 \begin{lstlisting}[language=Clean,caption={The \texttt{hb} bytecode instance}]
 141 :: BC
 142         = BCNop
 143         | ...
 144         | BCGetHB
 145         | BCGetSP02
 146
 147 instance hb ByteCode where
 148         getHb = tell` [BCGetHB]
 149         getSp02 = tell` [BCGetSP02]
 150 \end{lstlisting}
 151
 152 \subsubsection{Device Interface}
 153 The bytecode instructions are added but still the functionality needs to be
 154 added to the device interface to be implemented by clients. The following
 155 addition to \CI{interface.h} and the interpreter shows the added instructions.
 156 When adding a peripheral, the devices not having the peripheral do not need to
 157 have their code recompiled. New instructions always get a higher bytecode
 158 number if added correctly. The peripheral byte in the device specification by
 159 default shows a negative flag for every peripheral. Only the peripherals added
 160 will be flagged positive.
 161
 162 \begin{lstlisting}[language=Clean,caption={Adding the device interface}]
 163 // interface.h
 164 ...
 165 #if HAVEHB == 1
 166 uint16_t get_hb();
 167 uint16_t get_spo2();
 168 #endif
 169 ...
 170
 171 // interpret.c
 172         while(pc < plen){
 173                 switch(program[pc++]){
 174                 ...
 175 #if HAVEHB == 1
 176                 case BCGETHB:
 177                         stack[sp++] = get_hb();
 178                         break;
 179                 case BCGETSP02:
 180                         stack[sp++] = get_spo2();
 181                         break;
 182 #endif
 183                 ...
 184 \end{lstlisting}
 185
 186 \subsubsection{Client Software}
 187 The device client software always executes the \CI{real\_setup} in which the
 188 client software can setup the connection and peripherals. In the case of the
 189 heartbeat peripheral it starts a thread running the calculations. The thread
 190 started in the setup will set the global heartbeat and oxygen level variables
 191 so that the interface functions for it can access it. This is listed in
 192 Listing~\ref{lst:hbding}. If interrupts were implemented, the \glspl{Task}
 193 using the heartbeat sensor could be executed on interrupt. The heartbeat thread
 194 can fire an interrupt everytime it calculated a new heartbeat.
 195
 196 \begin{lstlisting}[label={lst:hbding},language=C,%
 197         caption={Heartbeat code in the client}]
 198 Serial pc;
 199 Thread thread;
 200
 201 void heartbeat_thread(void) {
 202         // Constant heartbeat calculations
 203 }
 204
 205 void real_setup(void) {
 206         pc.baud(19200);
 207         thread.start(heartbeat_thread);
 208 }
 209 \end{lstlisting}
 210
 211 \subsubsection{Example}
 212 The following code shows a complete example of a \gls{Task} controlling an
 213 \emph{STM} microcontroller containing a heartbeat sensor. The web application
 214 belonging to the server shows the heartbeat value and starts an alert
 215 \gls{Task} when it exceeds the value given or is no longer valid.
 216 This example also shows how named \gls{SDS} are handled.
 217
 218 \begin{lstlisting}[language=Clean,caption={Heartbeat example}]
 219 hbwatch :: (Task a) Int -> Task ()
 220 hbwatch alert lim
 221           =           makeDevice "stm32" stm32
 222         >>=           connectDevice
 223         >>= \stm    ->sendTaskToDevice "monitor" monitor (stm, OnInterval 200)
 224         >>= \(t, sh)->mon (fromJust $ find (\x->x.name == "hb") sh)
 225         >>* [OnAction (Action "Shutdown") $ always $ deleteDevice stm >>| shutDown 0]
 226 where
 227         mon :: (Shared BCValue) -> Task ()
 228         mon b = whileUnchanged (mapRead dynHB b)
 229                 \hb=:(HB i valid)->if (not valid || i > lim)
 230                         alert (viewInformation "HB Okay" [] hb)
 231
 232         dynHB :: Dynamic -> HeartBeat
 233         dynHB (a :: HeartBeat) = a
 234
 235         monitor = namedsds \hb=(0 Named hb) In
 236                 {main= hb = getHB :.  pub hb }
 237 \end{lstlisting}