\subsection{Framework}
-Systems built with support for \gls{mTask} are often following the same design
+Systems built with support for \gls{mTask} often follow the same design
pattern. First the devices are created --- with or without the interaction of
the user --- and they are then connected. When all devices are registered, the
\gls{mTask}-\glspl{Task} can be sent and \gls{iTasks}-\glspl{Task} can be
\subsection{Thermostat}
The thermostat is a classic example program for showing interactions between
peripherals. The following program shows a system containing two devices. The
-first device --- the sensor -- contains a temperature sensor that measures the
+first device --- the sensor --- contains a temperature sensor that measures the
room temperature. The second device --- the actor --- contains a heater,
-connected to the digital pin \CI{D5}. Moreover, this device contains a led to
-indicate whether the heater is on. The following code shows an implementation
-for this. The code fully uses the framework. Note that a little bit of type
-twiddling is required to fully us the result from the \gls{SDS}. This approach
-is still type safe due to the type safety of \CI{Dynamic}s.
+connected to the digital pin \CI{D5}. Moreover, this device contains an
+\gls{LED} to indicate whether the heater is on. The following code shows an
+implementation for this. The code makes use of all the aspects of the
+framework. Note that a little bit of type twiddling is required to fully use
+the result from the \gls{SDS}. This approach is still type safe due to the type
+safety of \CI{Dynamic}s.
\begin{lstlisting}[caption={Thermostat example}]
thermos :: Task ()
>>= \stm-> sendTaskToDevice "sensing" sensing (nod, OnInterval 1000)
>>= \(st, [t])->sendTaskToDevice "acting" acting (stm, OnInterval 1000)
(\(BCValue s)->set (BCValue $ dynInt (dynamic s) > 0) (shareShare nod a))
- >>| treturn ()
+ >>* [OnAction (Action "Shutdown") $ always $ deleteDevice nod >>| deleteDevice stm >>| shutDown 0]
where
dynInt :: Dynamic -> Int
dynInt (a :: Int) = a
\subsection[Lifting mTasks to iTasks-Tasks]%
{Lifting \gls{mTask}-\glspl{Task} to \gls{iTasks}-\glspl{Task}}
-If the user does not want to know where and when a \gls{mTask} is actually
-executed and is just interested in the results it can lift the \gls{mTask} to
+If the user does not want to know where and when an \gls{mTask} is actually
+executed and is just interested in the results, it can lift the \gls{mTask} to
an \gls{iTasks}-\gls{Task}. The function is called with a name, \gls{mTask},
device and interval specification and it will return a \gls{Task} that finishes
if and only if the \gls{mTask} has returned.
taskRemoved t d = isNothing $ find (\t1->t1.ident==t.ident) d.deviceTasks
\end{lstlisting}
-The factorial example can then be lifted to a real \gls{iTasks}-\gls{mTask}
-with the following code:
+The factorial function example from Chapter~\ref{chp:mtaskcont} can then be
+lifted to a real \gls{iTasks}-\gls{Task} with the following code:
\begin{lstlisting}[caption={Lifting the factorial \gls{Task} to \gls{iTasks}}]
factorial :: MTaskDevice -> Task BCValue
factorial dev = enterInformation "Factorial of ?" []
\subsection{Heartbeat \& Oxygen Saturation Sensor}
As an example, the addition of a new sensor will be demonstrated. The heartbeat
-and oxygen saturation sensor is a \textsc{PCB} the size of a fingernail with a
-red \gls{LED} and a light sensor on it. Moreover, it contains an \textsc{I2C}
-chip to communicate. The company producing the chip provides the programmer
-with example code for \gls{Arduino} and \textsc{mbed}. So suppose %TODO
-Adding peripheral is supposedly simple.
+and oxygen saturation sensor add-on is a \textsc{PCB} the size of a fingernail
+with a red \gls{LED} and a light sensor on it. Moreover, it contains an
+\textsc{I2C} chip to communicate. The company producing the chip provides the
+programmer with example code for \gls{Arduino} and \gls{mbed}. The sensor
+emits red light and measures the intensity of the light returned. The
+microcontroller hosting the device has to keep track of four seconds of samples
+to determine the heartbeat. In the \gls{mTask}-system, an abstraction is made.
+The current implementation runs on \gls{mbed} supported devices.
+
+\subsubsection{\gls{mTask} Classes}
+First, a class has to be devised to store the functionality of the sensor. The
+heartbeat sensor updates four values continuously, namely the heartbeat, the
+oxygen saturation and the validity of the two. For every value a function is
+added to the new \CI{hb} class. Moreover, the introduced datatype housing the
+values should implement the \CI{mTaskType} classes. The definition is as
+follows:
+
+\begin{lstlisting}[caption={The \texttt{hb} class}]
+:: Heartbeat = HB Int
+:: SP02 = SP02 Int
+
+instance toByteCode Heartbeat, SP02
+instance fromByteCode Heartbeat, SP02
+derive class iTask Heartbeat, SP02
+
+class hb v where
+ getHb :: (v Heartbeat Expr)
+ validHb :: (v Bool Expr)
+ getSp02 :: (v SP02 Expr)
+ validSp02 :: (v Bool Expr)
+\end{lstlisting}
+
+\subsubsection{Bytecode Implementation}
+The class is available now, and the implementation can be created. The
+implementation is trivial since the functionality is limited to retrieving
+single values and no assignment is possible. The following code shows the
+implementation. Dedicated bytecode instructions have been added to support the
+functionality.
+
+\begin{lstlisting}[caption={The \texttt{hb} bytecode instance}]
+:: BC
+ = BCNop
+ | ...
+ | BCGetHB
+ | BCValidHB
+ | BCGetSP02
+ | BCValidSP02
+
+instance hb ByteCode where
+ getHb = tell` [BCGetHB]
+ validHb = tell` [BCValidHB]
+ getSp02 = tell` [BCGetSP02]
+ validSp02 = tell` [BCValidSP02]
+\end{lstlisting}
+
+\subsubsection{Device Interface}
+The bytecode instructions are added but still the functionality needs to be
+added to the device interface to be implemented by clients. The following
+addition to \CI{interface.h} and the interpreter shows the added instructions.
+When adding a peripheral, the devices not having the peripheral do not need to
+have their code recompiled. New instructions always get a higher bytecode
+number if added correctly. The peripheral byte in the device specification by
+default shows a negative flag for every peripheral. Only the peripherals added
+will be flagged positive.
+
+\begin{lstlisting}[caption={Adding the device interface}]
+// interface.h
+...
+#if HAVEHB == 1
+uint16_t get_hb();
+bool valid_hb();
+uint16_t get_spo2();
+bool valid_spo2();
+#endif
+...
+
+// interpret.c
+ while(pc < plen){
+ switch(program[pc++]){
+ ...
+#if HAVEHB == 1
+ case BCGETHB:
+ stack[sp++] = get_hb();
+ break;
+ case BCVALIDHB:
+ stack[sp++] = valid_hb();
+ break;
+ case BCGETSP02:
+ stack[sp++] = get_spo2();
+ break;
+ case BCVALIDSP02:
+ stack[sp++] = valid_spo2();
+ break;
+#endif
+ ...
+\end{lstlisting}
+
+\subsubsection{Client Software}
+The device client software always executes the \CI{real\_setup} in which the
+client software can setup the connection and peripherals. In the case of the
+heartbeat peripheral it starts a thread running the calculations. The thread
+started in the setup will set the global heartbeat and oxygen level variables
+so that the interface functions for it can access it. The code is then as
+follows:
+
+\begin{lstlisting}[language=C,caption={}]
+Serial pc;
+Thread thread;
+
+void heartbeat_thread(void) {
+ // Constant heartbeat calculations
+}
+
+void real_setup(void) {
+ pc.baud(19200);
+ thread.start(heartbeat_thread);
+}
+\end{lstlisting}
repositories / msc-thesis1617.git / blobdiff