results.arch.tex

   1 The goal of the total system is to facilitate an ecosystem in which an
   2 \gls{iTasks}-system can add, change and remove devices at runtime. Moreover,
   3 the \gls{iTasks}-system can send \glspl{mTask} --- compiled at runtime to
   4 bytecode by the \gls{mTask}-view --- to the device. The device runs an
   5 interpreter which can execute the \gls{Task}'s bytecode. Device profiles should
   6 be persistent during reboots of the \gls{iTasks}-system. The methods of
   7 interacting with \glspl{mTask} should be analogous to interacting with
   8 \gls{iTasks}-\glspl{Task}. This means that programmers can access the
   9 \glspl{SDS} made for a device in the same way as a regular \gls{SDS} and they
  10 can execute \glspl{mTask} as if it where a normal \gls{iTasks}-\gls{Task}.
  11
  12 The following terms will be used throughout the following chapter:
  13 \begin{itemize}
  14         \item Device, Client
  15
  16                 This denotes the actual device connected to the system. This can be a
  17                 real device such as a microcontroller but it can also just be a program
  18                 on the same machine as the server functioning as a client.
  19         \item Server, \gls{iTasks}-System
  20
  21                 This is the actual executable serving the \gls{iTasks} application. The
  22                 system contains \glspl{Task} taking care of the communication with the
  23                 clients.
  24         \item System
  25
  26                 The system describes the complete ecosystem, containing both the server
  27                 and the clients including the communication between them.
  28         \item Engine
  29
  30                 The runtime system of the client is called the engine. This program
  31                 handles communicating with the server and runs the interpreter for the
  32                 \glspl{Task} on the client.
  33 \end{itemize}
  34
  35 \section{Devices}
  36 A device is suitable for the system if it can run the engine.
  37 The engine is compiled from one codebase and devices implement (part of) the
  38 device specific interface. The shared codebase only uses standard \gls{C} and
  39 no special libraries or tricks are used. Therefore, the code is compilable for
  40 almost any device or system. Note that it is not needed to implement a full
  41 interface. The full interface --- excluding the device specific settings --- is
  42 listed in Appendix~\ref{app:device-interface}.  The interface works in a
  43 similar fashion as the \gls{EDSL}. Devices do not have to implement all
  44 functionality, this is analogous to the fact that views do not have to
  45 implement all type classes in the \gls{EDSL}.  When the device connects with
  46 the server for the first time, the specifications of what is implemented is
  47 communicated.
  48
  49 At the time of writing the following device families are supported and can run
  50 the device software.
  51 \begin{itemize}
  52         \item \texttt{POSIX} compatible systems connected via \gls{TCP}.
  53
  54                 This includes systems running \emph{Linux} and \emph{MacOS}.
  55         \item \texttt{STM32} family microcontrollers supported by \texttt{ChibiOS}
  56                 connected via serial communication.
  57
  58                 This is tested in particular on the \texttt{STM32f7x} series \gls{ARM}
  59                 development board.
  60         \item Microcontrollers that are programmable in the \gls{Arduino} \gls{IDE}
  61                 connected via serial communication or via \gls{TCP} over WiFi.
  62
  63                 This does not only include \gls{Arduino} compatible boards but also
  64                 other boards capable of running \gls{Arduino} code. A port of the
  65                 client has been made for the \texttt{ESP8266} powered \emph{NodeMCU}
  66                 that is connected via \gls{TCP} over WiFi. A port also has been made
  67                 for the regular \gls{Arduino} \emph{UNO} board which only boasts a
  68                 meager \emph{2K} \emph{RAM}. The stack size and storage available for
  69                 devices boasting this little \emph{RAM} has to be smaller than default
  70                 but is still suitable to hold a hand full of \glspl{Task}.
  71 \end{itemize}
  72
  73 \subsection{Client}
  74 \subsubsection{Engine}
  75 The client is in a constant loop listening for input and waiting to execute
  76 \gls{Task}. The pseudocode for this is shown in Algorithm~\ref{alg:client}. The
  77 \CI{input\_available} function waits for input, but has a timeout set which can
  78 be interrupted. The timeout of the function determines the amount of loops per
  79 time interval and is a parameter that can be set during compilation for a
  80 device.
  81
  82 \begin{algorithm}[H]
  83         \KwData{
  84                 \textbf{list} $tasks$,
  85                 \textbf{time} $t$
  86         }
  87
  88         \Begin{
  89                 \While{true}{
  90                         \If{input\_available$()$}{
  91                                 receive\_data()\;
  92                         }
  93
  94                         $t\leftarrow \text{now}()$\;
  95                         \ForEach{$t\leftarrow tasks$}{
  96                                 \uIf{is\_interrupt$(t) \&\& $had\_interrupt$(t)$}{
  97                                         run\_task$(t)$\;
  98                                 }
  99                                 \ElseIf{$t-t.\text{lastrun} > t.\text{interval}$}{
 100                                         run\_task$(t)$\;
 101                                         \uIf{$t.\text{interval}==0$}{
 102                                                 delete\_task$(t)$\;
 103                                         }\Else{
 104                                                 $t.\text{lastrun}\leftarrow t$\;
 105                                         }
 106                                 }
 107                         }
 108                 }
 109         }
 110         \caption{Engine pseudocode}\label{alg:client}
 111 \end{algorithm}
 112
 113 \subsubsection{Storage}
 114 \glspl{Task} and \glspl{SDS} are stored on the client in one big memory space
 115 that is reserved at the start of the program. The space could also have been
 116 dynamically allocated but that would require using the heap which is unwanted
 117 in small memory environments. \Glspl{Task} grow from the bottom up and
 118 \glspl{SDS} grow from the top down. When a \gls{Task} or \gls{SDS} is removed,
 119 all \glspl{Task} are relocated in the memory space to not leave holes. Both
 120 \glspl{Task} and \glspl{SDS} are stored as structures that are linked in the
 121 memory space, helper functions are available to loop through them without
 122 having to fiddle in the memory space itself. The instance for \glspl{Task} and
 123 \glspl{SDS} are shown in Listing~\ref{lst:structs} accompanied by the helper
 124 functions for \glspl{Task}. \Glspl{Task} consists of the length, interval, last
 125 run time, id and the bytecode. \Glspl{SDS} consist only of an id, value and
 126 type. The pointer to the bytecode of the \gls{Task} always points to the
 127 location in the memory space.
 128
 129 \begin{lstlisting}[language=C,label={lst:structs},%
 130         caption={The data type storing the \glspl{Task}}]
 131 struct task {
 132         uint16_t tasklength;
 133         uint16_t interval;
 134         unsigned long lastrun;
 135         uint8_t taskid;
 136         uint8_t *bc;
 137 };
 138
 139 struct task *task_head(void);
 140 struct task *task_next(struct task *t);
 141
 142 struct sds {
 143         int id;
 144         int value;
 145         char type;
 146 };
 147
 148 struct sds *sds_head(void);
 149 struct sds *sds_next(struct sds *s);
 150 \end{lstlisting}
 151
 152 \subsubsection{Interpretation}
 153 The execution of a \gls{Task} is started by running the \CI{run\_task} function
 154 and always start with prepared the stack and the program counter and stack
 155 pointer are set to zero and the bottom respectively. When finished, the
 156 interpreter executes one step at the time while the program counter is smaller
 157 than the program length. This code is listed in Listing~\ref{lst:interpr}. One
 158 execution step is basically a big switch statement going over all possible
 159 bytecode instructions. Some instructions are detailed upon in the listing. The
 160 \CI{BCPush} instruction is a little more complicated in the real code because
 161 some decoding will take place as not all \CI{BCValue}s are of the same length
 162 and are encoded.
 163
 164 \begin{lstlisting}[language=C,label={lst:interpr},%
 165         caption={Rough code outline for interpretation}]
 166 #define f16(p) program[pc]*265+program[pc+1]
 167
 168 void run_task(struct task *t){
 169         uint8_t *program = t->bc;
 170         int plen = t->tasklength;
 171         int pc = 0;
 172         int sp = 0;
 173         while(pc < plen){
 174                 switch(program[pc++]){
 175                 case BCNOP:
 176                         break;
 177                 case BCPUSH:
 178                         stack[sp++] = pc++ //Simplified
 179                         break;
 180                 case BCPOP:
 181                         sp--;
 182                         break;
 183                 case BCSDSSTORE:
 184                         sds_store(f16(pc), stack[--sp]);
 185                         pc+=2;
 186                         break;
 187                 // ...
 188                 case BCADD: trace("add");
 189                         stack[sp-2] = stack[sp-2] + stack[sp-1];
 190                         sp -= 1;
 191                         break;
 192                 // ...
 193                 case BCJMPT: trace("jmpt to %d", program[pc]);
 194                         pc = stack[--sp] ? program[pc]-1 : pc+1;
 195                         break;
 196 }
 197 \end{lstlisting}
 198
 199 \subsection{Specification}
 200 The server stores a description for every device available in a record type.
 201 From the macro settings in the interface file, a profile is created that
 202 describes the specification of the device. When the connection between the
 203 server and a client is established, the server will send a request for
 204 specification. The client will serialize his specification and send it to the
 205 server so that the server knows what the client is capable of.  The exact
 206 specification is shown in Listing~\ref{lst:devicespec} and stores the
 207 peripheral availability, the memory available for storing \glspl{Task} and
 208 \glspl{SDS} and the size of the stack.
 209
 210 \begin{lstlisting}[label={lst:devicespec},
 211         caption={Device specification for \glspl{mTask}}]
 212 :: MTaskDeviceSpec =
 213         { haveLed     :: Bool
 214         , haveLCD     :: Bool
 215         , have...
 216         , bytesMemory :: Int
 217         , stackSize   :: Int
 218         , aPins       :: Int
 219         , dPins       :: Int
 220         }
 221 \end{lstlisting}
 222
 223 \section{iTasks}
 224 The server part of the system is written in \gls{iTasks}. Functions for
 225 managing devices, \glspl{Task} and \glspl{SDS} have been created to support the
 226 functionality. An interactive application has been created that allows an
 227 interactive management console for the \gls{mTask} system. This interface
 228 provides functionality to list \glspl{SDS}, add \glspl{Task}, remove
 229 \glspl{Task}, administrate devices and view the state of the system.
 230
 231 \subsection{Device Storage}
 232 Everything that a device encompasses is stored in the \CI{MTaskDevice} record
 233 type. This includes management for the \glspl{SDS} and \glspl{Task} stored on
 234 the device. The \CI{MTaskDevice} definition is shown in
 235 Listing~\ref{lst:mtaskdevice} accompanied with the necessary classes and sub
 236 types.
 237
 238 \begin{lstlisting}[caption={Device type},label={lst:mtaskdevice}]
 239 :: Channels :== ([MTaskMSGRecv], [MTaskMSGSend], Bool)
 240 :: BCState = ... // Compiler state, explained in later sections
 241 :: MTaskResource
 242         = TCPDevice TCPSettings
 243         | SerialDevice TTYSettings
 244         | ...
 245 :: MTaskDevice =
 246                 { deviceTask :: Maybe TaskId
 247                 , deviceError :: Maybe String
 248                 , deviceChannels :: String
 249                 , deviceName :: String
 250                 , deviceState :: BCState
 251                 , deviceTasks :: [MTaskTask]
 252                 , deviceData :: MTaskResource
 253                 , deviceSpec :: Maybe MTaskDeviceSpec
 254                 , deviceShares :: [MTaskShare]
 255         }
 256
 257 channels :: MTaskDevice -> Shared Channels
 258
 259 class MTaskDuplex a where
 260         synFun :: a (Shared Channels) -> Task ()
 261 \end{lstlisting}
 262
 263 The \CI{deviceResource} component of the record must implement the
 264 \CI{MTaskDuplex} interface that provides a function that launches a \gls{Task}
 265 used for synchronizing the channels. The \CI{deviceTask} stores the
 266 \gls{Task}-id for this \gls{Task} when active so that it can be checked upon.
 267 This top-level task has the duty to report exceptions and errors as they are
 268 thrown by setting the \CI{deviceError} field. All communication goes via these
 269 channels. To send a message to the device, the system just puts it
 270 in the channels. Messages sent from the client to the server are also placed
 271 in there. In the case of the \gls{TCP} device type, the \gls{Task} is just a
 272 simple wrapper around the existing \CI{tcpconnect} function in \gls{iTasks}. In
 273 case of a device connected by a serial connection, it uses the newly developed
 274 serial port library of \gls{Clean}\footnote{\url{%
 275 https://gitlab.science.ru.nl/mlubbers/CleanSerial}}.
 276
 277 Besides all the communication information, the record also keeps track of the
 278 \glspl{Task} currently on the device, the compiler state (see
 279 Section~\ref{sec:compiler}) and the according \glspl{SDS}. Finally, it stores
 280 the specification of the device that is received when connecting. All of this
 281 is given in Listing~\ref{lst:mtaskdevice}. The definitions of the message
 282 format are explained in the following section.
 283
 284 \subsection{Shares}
 285 The architecture of the system keeps track of the \glspl{SDS} stored on
 286 the client in a big \gls{SDS} containing a list of devices. Client-\glspl{SDS}
 287 can be stored on one device at the same time. This means that if a \gls{SDS}
 288 updates, everyone watching it will be notified. This would result in a lot
 289 of notifications that are not meant for the watcher. Moreover, when a client
 290 updates the \gls{SDS} this is processed by the connection handler and results
 291 in an update of the real \gls{SDS}. Finally, the \gls{SDS} of a client must be
 292 synchronized with the actual device. Thus, when an \gls{iTasks}-\gls{Task}
 293 writes the client-\gls{SDS}, it must be propagated to the real device. There
 294 are several ways of tackling this problem, each with their own pros and cons and
 295 their own level of abstraction.
 296
 297 First an actual \gls{iTasks}-\gls{SDS} for every \gls{SDS} used in a client can
 298 be instantiated with one \gls{iTasks}-\gls{Task} listening to the \gls{SDS} and
 299 synchronizing it with the device when an update occurred. This approach is very
 300 expensive as it requires a lot of listening \glspl{Task}.
 301
 302 Improved on this, a single \gls{iTasks}-\gls{SDS} can be created for every
 303 devices that stores the respective \glspl{SDS}. Using the \CI{mapReadWrite}
 304 functions, a single \gls{SDS} per device can be created as a lens that allows
 305 mapping on a single client-\gls{SDS}. However, this approach still requires
 306 \glspl{Task} listening to the \gls{SDS} and when a \gls{SDS} is written,
 307 everyone is notified, even if the \gls{Task} only uses the value of a single
 308 different \gls{SDS}.
 309
 310 Ultimately, the current approach --- a single \gls{SDS} for the entire system
 311 --- was explored. To create \glspl{SDS} per device or per client-\glspl{SDS} a
 312 \CI{mapReadWrite} can be used but it suffers from the same problem as mentioned
 313 before. Moreover, a \gls{Task} still has to watch the \gls{SDS} and communicate
 314 the client-\gls{SDS} updates to the actual device. Both of these problems can
 315 be solved by using a tailor made share that heavily depends on parametric
 316 lenses.
 317
 318 \subsection{Parametric Lenses}
 319 The type of the parametric lens is \CI{Maybe (MTaskDevice, Int)}. The \gls{SDS}
 320 can be responsible for the entire list of devices, from now on global.
 321 Moreover, the \gls{SDS} can focus on a single device, from now on local. A
 322 local \gls{SDS} can also specifically focus on a single \gls{SDS} on a single
 323 device, from now on called local-share. The implementation of the real
 324 \gls{SDS} is given in Listing~\ref{lst:actualdev}. The \gls{SDS} is a lens on
 325 an actual \gls{SDS} that writes to a file or memory. Reading the \gls{SDS} is
 326 nothing more than reading the real \gls{SDS}. Writing the \gls{SDS} is a little
 327 bit more involved. If the write operation originated from a \gls{SDS} focussed
 328 on a single client-\gls{SDS}, the write action must also be relayed to the
 329 actual device. If the write originated from a \gls{SDS} focussed the devices or
 330 on one device only, nothing needs to be done. The notification predicate
 331 determines whether a watcher gets a notification update.
 332
 333 \begin{lstlisting}[label={lst:actualdev},%
 334         caption={Device \gls{SDS}}]
 335 deviceStore :: RWShared (Maybe (MTaskDevice, Int)) [MTaskDevice] [MTaskDevice]
 336 deviceStore = SDSSource {SDSSource | name="deviceStore", read = realRead, write= realWrite}
 337 where
 338         realRead :: (Maybe (MTaskDevice,Int)) *IWorld -> (MaybeError TaskException [MTaskDevice], *IWorld)
 339         realRead p iw = read realDeviceStore iw
 340
 341         realWrite :: (Maybe (MTaskDevice,Int)) [MTaskDevice] *IWorld -> (MaybeError TaskException (SDSNotifyPred (Maybe (MTaskDevice,Int))), *IWorld)
 342         realWrite mi w iw
 343         # (merr, iw) = write w realDeviceStore iw
 344         | isError merr || isNothing mi = (merr $> notifyPred mi, iw)
 345         # (Just (dev, ident)) = mi
 346         | ident == -1 = (merr $> notifyPred mi, iw)
 347         = case find ((==)dev) w of
 348                 Nothing = (Error $ exception "Device lost", iw)
 349                 Just {deviceShares} = case find (\d->d.identifier == ident) deviceShares of
 350                         Nothing = (Error $ exception "Share lost", iw)
 351                         Just s = case sendMessagesIW [MTUpd ident s.MTaskShare.value] dev iw of
 352                                 (Error e, iw) = (Error e, iw)
 353                                 (Ok _, iw) = (Ok $ notifyPred mi, iw)
 354
 355         notifyPred :: (Maybe (MTaskDevice, Int)) (Maybe (MTaskDevice, Int)) -> Bool
 356         notifyPred Nothing Nothing = True    // Global watcher looking at a global event
 357         notifyPred Nothing (Just _) = False  // Global watcher looking at a local event
 358         notifyPred (Just _) Nothing = False  // Local watcher looking at a global event
 359         // Local device watcher looking at a local event
 360         notifyPred (Just (d1, -1)) (Just (d2, _)) = d1 == d2
 361         // Local share watcher looking at a local share event
 362         notifyPred (Just (d1, i1)) (Just (d2, i2)) = d1 == d2 && i1 == i2
 363
 364         realDeviceStore :: Shared [MTaskDevice]
 365         realDeviceStore = sharedStore "mTaskDevices" []
 366 \end{lstlisting}
 367
 368 \subsubsection{Global \glspl{SDS}}
 369 Accessing the global \gls{SDS} is just a matter of focussing the
 370 \CI{deviceStore} with the \CI{Nothing} parameter as follows:
 371
 372 \begin{lstlisting}[caption={Global \gls{SDS}}]
 373 deviceStoreNP :: Shared [MTaskDevice]
 374 deviceStoreNP = sdsFocus Nothing deviceStore
 375 \end{lstlisting}
 376
 377 \subsubsection{Local \glspl{SDS}}
 378 Accessing a single device can be done using the \CI{mapReadWrite} function.
 379 Since device comparison is shallow, the device that is given is allowed to be
 380 an old version. The identification of devices is solely done on the name of the
 381 channels and is unique throughout the system. The implementation is as follows:
 382
 383 \begin{lstlisting}[caption={Local \gls{SDS}}]
 384 deviceShare :: MTaskDevice -> Shared MTaskDevice
 385 deviceShare d = mapReadWriteError
 386         ( \ds->case find ((==)d) of
 387                 Nothing = exception "Device lost"
 388                 Just d = Ok d)
 389         , \w ds->case splitWith ((==)d) ds of
 390                 ([], _) = Error $ exception "Device lost"
 391                 ([_:_], ds) = Ok $ Just [w:ds])
 392         $ sdsFocus (Just (d, -1)) deviceStore
 393 \end{lstlisting}
 394
 395 \subsubsection{Local-share specific \glspl{SDS}}
 396 A single \gls{SDS} on a single device can be accessed using the \CI{shareShare}
 397 function. This function focusses the real big \gls{SDS} on a single share and
 398 uses the \CI{mapReadWrite} functions to serve the correct part of the
 399 information.
 400
 401 \begin{lstlisting}[caption={Local \gls{SDS}}]
 402 shareShare :: MTaskDevice MTaskShare -> Shared BCValue
 403 shareShare dev share = sdsFocus ()
 404         $ mapReadWriteError (read, write)
 405         $ sdsFocus (Just (dev, share.identifier))
 406         $ deviceStore
 407 where
 408         read :: [MTaskDevice] -> MaybeError TaskException BCValue
 409         read devs = case find ((==)dev) devs of
 410                 Nothing = exception "Device lost"
 411                 Just d = case find ((==)share) d.deviceShares of
 412                         Nothing = exception "Share lost"
 413                         Just s = Ok s.MTaskShare.value
 414
 415         write :: BCValue [MTaskDevice] -> MaybeError TaskException (Maybe [MTaskDevice])
 416         write val devs = case partition ((==)dev) devs of
 417                 ([], _) = Error $ exception "Device doesn't exist anymore"
 418                 ([_,_:_], _) = Error $ exception "Multiple matching devices"
 419                 ([d=:{deviceShares}], devs) = case partition ((==)share) deviceShares of
 420                         ([], _) = Error $ exception "Share doesn't exist anymore"
 421                         ([_,_:_], _) = Error $ exception "Multiple matching shares"
 422                         ([s], shares) = Ok $ Just [{MTaskDevice | d &
 423                                 deviceShares=[{MTaskShare | s & value=val}:shares]}:devs]
 424 \end{lstlisting}
 425
 426 \section{Communication}
 427 The communication from the server to the client and vice versa is just a
 428 character stream containing encoded \gls{mTask} messages. The \CI{synFun}
 429 belonging to the device is responsible for sending the content in the left
 430 channel and putting received messages in the right channel. Moreover, the
 431 boolean value should be set to \CI{True} when the connection is terminated. The
 432 specific encoding of the messages is visible in
 433 Appendix~\ref{app:communication-protocol}. The type holding the messages is
 434 shown in Listing~\ref{lst:avmsg}. Detailed explanation about the message types
 435 and according actions will be given in the following subsections.
 436
 437 \begin{lstlisting}[label={lst:avmsg},caption={Available messages}]
 438 :: MTaskId :== Int
 439 :: MSDSId :== Int
 440 :: MTaskFreeBytes :== Int
 441 :: MTaskMSGRecv
 442         = MTTaskAck MTaskId MTaskFreeBytes | MTTaskDelAck MTaskId
 443         | MTSDSAck MSDSId                  | MTSDSDelAck MSDSId
 444         | MTPub MSDSId BCValue             | MTMessage String
 445         | MTDevSpec MTaskDeviceSpec        | MTEmpty
 446
 447 :: MTaskMSGSend
 448         = MTTask MTaskInterval String | MTTaskDel MTaskId
 449         | MTShutdown                  | MTSds MSDSId BCValue
 450         | MTUpd MSDSId BCValue        | MTSpec
 451
 452 :: MTaskInterval = OneShot | OnInterval Int | OnInterrupt Int
 453 \end{lstlisting}
 454
 455 \subsection{Add a device}
 456 A device can be added by filling in the \CI{MTaskDevice} record as much as
 457 possible and running the \CI{connectDevice} function. This function grabs the
 458 channels, starts the synchronization \gls{Task} (\CI{synFun}), makes sure the
 459 errors are handled when needed and runs a processing function in parallel to
 460 react on the incoming messages. Moreover, it sends a specification request to
 461 the device in question to determine the details of the device and updates the
 462 record to contain the top-level \gls{Task}-id. All device functionality
 463 heavily depends on the specific \CI{deviceShare} function that generates an
 464 \gls{SDS} for a specific device. This allows giving an old device record to the
 465 function and still update the latest instance. Listing~\ref{lst:connectDevice}
 466 shows the connection function.
 467
 468 \begin{lstlisting}[label={lst:connectDevice},%
 469         caption={Connect a device}]
 470 connectDevice :: (MTaskDevice (Shared Channels) -> Task ()) MTaskDevice -> Task Channels
 471 connectDevice procFun device = let ch = channels device
 472         in traceValue "connectDevice" >>| appendTopLevelTask 'DM'.newMap True
 473                 (       procFun device ch -||- catchAll (getSynFun device.deviceData ch) errHdl)
 474                 >>= \tid->upd (\d->{d&deviceTask=Just tid,deviceError=Nothing}) (deviceShare device)
 475                 >>| upd (\(r,s,ss)->(r,s++[MTSpec],ss)) ch
 476 where
 477         errHdl e = upd (\d->{d & deviceTask=Nothing, deviceError=Just e}) (deviceShare device) @! ()
 478 \end{lstlisting}
 479
 480 Figure~\ref{fig:handshake} shows the connection diagram. The client responds to
 481 the server with their device specification. This is detected by the processing
 482 function and the record is updated accordingly.
 483
 484 \begin{figure}[H]
 485         \centering
 486         \begin{sequencediagram}
 487                 \newthread{s}{Server}
 488                 \newinst[4]{c}{Client}
 489                 \begin{call}{s}{MTSpec}{c}{MTDevSpec}
 490                 \end{call}
 491         \end{sequencediagram}
 492         \caption{Connect a device}\label{fig:handshake}
 493 \end{figure}
 494
 495 \subsection{\glspl{Task} \& \glspl{SDS}}
 496 When a \gls{Task} is sent to the device it is added to the device record
 497 without an identifier. The actual identifier is added to the record when the
 498 acknowledgement of the \gls{Task} by the device is received. The connection
 499 diagram is shown in Figure~\ref{fig:tasksend}.
 500
 501 \begin{figure}[H]
 502         \centering
 503         \begin{sequencediagram}
 504                 \newthread{s}{Server}
 505                 \newinst[4]{c}{Client}
 506                 \begin{call}{s}{MTSDS}{c}{MTSDSAck}
 507                 \end{call}
 508                 \begin{call}{s}{MTTask}{c}{MTTaskAck}
 509                 \end{call}
 510         \end{sequencediagram}
 511         \caption{Sending a \gls{Task} to a device}\label{fig:tasksend}
 512 \end{figure}
 513
 514 The function for sending a \gls{Task} to the device is shown in
 515 Listing~\ref{lst:sendtask}. First the \gls{Task} is compiled into messages. The
 516 details of the compilation process are given in Section~\ref{sec:compiler}.
 517 The new \glspl{SDS} that were generated during compilation are merged with the
 518 existing device's \glspl{SDS}. Furthermore the messages are placed in the
 519 channel \gls{SDS} of the device. This will result in sending the actual \gls{SDS}
 520 specification and \gls{Task} specifications to the device. A \gls{Task} record
 521 is created with the identifier $-1$ to denote a \gls{Task} not yet
 522 acknowledged. Finally the device itself is updated with the new state and with
 523 the new \gls{Task}.  After waiting for the acknowledgement the device is
 524 updated again and the \gls{Task} returns.
 525
 526 \begin{lstlisting}[label={lst:sendtask},%
 527         caption={Sending a \gls{Task} to a device}]
 528 makeTask :: String Int -> Task MTaskTask
 529 makeTask name ident = get currentDateTime @ \dt->{MTaskTask | name=name, ident=ident, dateAdded=dt}
 530
 531 makeShare :: String Int BCValue -> MTaskShare
 532 makeShare withTask identifier value = {MTaskShare | withTask=[withTask], identifier=identifier, value=value}
 533
 534 sendTaskToDevice :: String (Main (ByteCode a Stmt)) (MTaskDevice, MTaskInterval) -> Task MTaskTask
 535 sendTaskToDevice wta mTask (device, timeout)
 536 # (msgs, newState=:{sdss}) = toMessages timeout mTask device.deviceState
 537 # shares = [makeShare wta "" sdsi sdsval\\{sdsi,sdsval}<-sdss, (MTSds sdsi` _)<-msgs | sdsi == sdsi`]
 538 = updateShares device ((++) shares)
 539         >>| sendMessages msgs device
 540         >>| makeTask wta -1
 541         >>= \t->upd (addTaskUpState newState t) (deviceShare device)
 542         >>| wait "Waiting for task to be acked" (taskAcked t) (deviceShare device)
 543         >>| treturn t
 544 where
 545         addTaskUpState :: BCState MTaskTask MTaskDevice -> MTaskDevice
 546         addTaskUpState st task device = {MTaskDevice | device & deviceState=st, deviceTasks=[task:device.deviceTasks]}
 547         taskAcked t d = maybe True (\t->t.ident <> -1) $ find (eq t) d.deviceTasks
 548         eq t1 t2 = t1.dateAdded == t2.dateAdded && t1.MTaskTask.name == t2.MTaskTask.name
 549 \end{lstlisting}
 550
 551 \subsection{Miscellaneous Messages}
 552 One special type of message is available which is sent to the device only when
 553 it needs to reboot. When the server wants to stop the bond with the device it
 554 sends the \CI{MTShutdown} message. The device will then clear its memory, thus
 555 losing all the \glspl{SDS} and \glspl{Task} that were stored and reset itself.
 556 Shortly after the shutdown message a new server can connect to the device
 557 because the device is back in listening mode.
 558
 559 \subsection{Integration}
 560 When the system starts up, the devices from the previous execution still
 561 residing in the \gls{SDS} must be cleaned up. It might be the case that they
 562 contain \glspl{Task}, \glspl{SDS} or errors that are no longer applicable in
 563 this run. A user or programmer can later choose to reconnect to some devices.
 564
 565 \begin{lstlisting}[caption={Starting up the devices},%
 566         label={lst:startupdevs}]
 567 startupDevices :: Task [MTaskDevice]
 568 startupDevices = upd (map reset) deviceStoreNP
 569         where reset d = {d & deviceTask=Nothing, deviceTasks=[], deviceError=Nothing}
 570 \end{lstlisting}
 571
 572 The system's management is done through the interface of a single \gls{Task}
 573 called \CI{mTaskManager}. To manage the system, a couple of different
 574 functionalities are needed and are launched. An image of the management
 575 interface is shown in Figure~\ref{lst:manage}. The left sidebar of the
 576 interface shows the list of example \glspl{Task} that are present in the
 577 system. When clicking a \gls{Task}, a dialog opens in which a device can be
 578 selected to send the \gls{Task} to. The dialog might contain user specified
 579 variables. All example \glspl{mTask} are of the type \CI{Task (Main (ByteCode
 580 () Stmt))} and can thus ask for user input first if needed for parameterized
 581 \glspl{mTask}. The bottom panel shows the device information. In this panel,
 582 the devices can be created and modified. Moreover, this panel allows the user
 583 to reconnect with a device after a restart of the server application.
 584
 585 \todo{redo this image}
 586 \begin{figure}[H]
 587         \centering
 588         \includegraphics[width=\linewidth]{manage}
 589         \caption{The device management interface}\label{lst:manage}
 590 \end{figure}
 591
 592 \section[Lifting mTasks to iTasks-Tasks]%
 593         {Lifting \glspl{mTask} to \gls{iTasks}-\glspl{Task}}
 594 If the user does not want to know where and when a \gls{mTask} is actually
 595 executed and is just interested in the results it can lift the \gls{mTask} to
 596 an \gls{iTasks}-\glspl{Task}. The function is called with a name, \gls{mTask},
 597 device and interval specification and it will return a \gls{Task} that finishes
 598 if and only if the \gls{mTask} has returned.
 599
 600 \begin{lstlisting}[caption={Starting up the devices}]
 601 liftmTask :: String (Main (ByteCode () Stmt)) (MTaskDevice, MTaskInterval) -> Task ()
 602 liftmTask wta mTask c=:(dev, _)= sendTaskToDevice wta mTask c
 603         >>= \t->wait "Waiting for mTask to return" (taskRemoved t) (deviceShare dev)
 604         >>| viewInformation "Done!" [] ()
 605 where
 606         taskRemoved t d = isNothing $ find (\t1->t1.ident==t.ident) d.deviceTasks
 607 \end{lstlisting}
 608
 609 \section{Examples}
 610 \todo{example program (demo)}