-The \glspl{Task} suitable for a client are called \glspl{mTask} and are written
-in the aforementioned \gls{mTask}-\gls{EDSL}. Some functionality of the
-original \gls{mTask}-\gls{EDSL} will not be used in this system. Conversely,
-some functionality needed was not available in the existing \gls{EDSL}. Due to
-the nature of class based shallow embedding this obstacle is easy to
-solve. A type --- housing the \gls{EDSL} --- does not have to implement all the
-available classes. Moreover, classes can be added at will without interfering
-with the existing views.
+The \glspl{Task} suitable for a client are called \gls{mTask}-\gls{Task} and
+are written in the aforementioned \gls{mTask}-\gls{EDSL}. Some functionality of
+the original \gls{mTask}-\gls{EDSL} will not be used in this system.
+Conversely, some functionality needed was not available in the existing
+\gls{EDSL}. Due to the nature of class based shallow embedding this obstacle is
+easy to solve. A type --- housing the \gls{EDSL} --- does not have to implement
+all the available classes. Moreover, classes can be added at will without
+interfering with the existing views.
\section{\gls{Task} Semantics}
The current \gls{mTask} engine for devices does not support \glspl{Task} in the
\item\CI{OnInterrupt}
The last scheduling method is running \glspl{Task} on a specific
- interrupt. None of the current client implementations support this.
- However, registering interrupts on, for example the \gls{Arduino} is
- very straightforward. Interrupt scheduling is useful for \glspl{Task}
- that have to react on a certain type of hardware event such as the
- press of a button.
+ interrupt. Unfortunatly, due to time constraints and focus, none of the
+ current client implementations support this. Interrupt scheduling is
+ useful for \glspl{Task} that have to react on a certain type of
+ hardware event such as the press of a button.
\end{itemize}
\section{\gls{SDS} semantics}
\Glspl{SDS} on a client are available on the server as well as regular
-\gls{SDS}. However, the same freedom is not given on the \glspl{SDS} that
-reside on the client. Not all types are suitable to be located on a client.
-Moreover, \glspl{SDS} behave a little different on an \gls{mTask} device
-compared to the \gls{iTasks} system. In an \gls{iTasks} system, when the
+\glspl{SDS}. However, the same freedom is not given for \glspl{SDS} that
+reside on the client. Not all types are suitable to be located on a client,
+simply because it needs to be serializable and representable on clients.
+Moreover, \glspl{SDS} behave a little different in an \gls{mTask} device
+compared to in the \gls{iTasks} system. In an \gls{iTasks} system, when the
\gls{SDS} is updated, a broadcast to all watching \glspl{Task} in the system
is made to notify them of the update. \glspl{SDS} can update often and the
-update might not be the final value it will get. This results in a lot of
-expensive unneeded bandwidth usage. Therefore a device must publish the
-\gls{SDS} explicitly to save bandwidth.
+update might not be the final value it will get. Implementing the same
+functionality on the \gls{mTask} client would result in a lot of expensive
+unneeded bandwidth usage. Therefore a device must publish the \gls{SDS}
+explicitly to save bandwidth.
To add this functionality, the \CI{sds} class could be extended. However, this
would result in having to update all existing views that use the \CI{sds}
\end{lstlisting}
\section{Bytecode compilation view}\label{sec:compiler}
-The \glspl{mTask} are sent to the device in bytecode and are saved in the
-memory of the device. To compile the \gls{EDSL} code to bytecode, a view is
-added to the \gls{mTask}-system encapsulated in the type \CI{ByteCode}. As
+The \gls{mTask}-\glspl{Task} are sent to the device in bytecode and are saved
+in the memory of the device. To compile the \gls{EDSL} code to bytecode, a view
+is added to the \gls{mTask}-system encapsulated in the type \CI{ByteCode}. As
shown in Listing~\ref{lst:bcview}, the \CI{ByteCode} view is a boxed \gls{RWST}
that writes bytecode instructions (\CI{BC}, Subsection~\ref{sec:instruction})
while carrying around a \CI{BCState}. The state is kept between compilations
\subsection{Instruction Set}\label{sec:instruction}
The instruction set is given in Listing~\ref{bc:instr}. The instruction set is
-kept large, but under $255$, to get the highest expressivity while keeping all
-instruction within one byte.
+kept large, but under $255$, to get as much expressieve power as possible while
+keeping all instruction within one byte.
The interpreter running in the client is a stack machine. The virtual
instruction \CI{BCLab} is added to allow for an easy implementation of jumping.
| BCReturn
\end{lstlisting}
-All single byte instructions are converted automatically using the generic
-function \CI{consIndex} which returns the index of the constructor. The index
-of the constructor is the byte value for all instructions. The last step of the
+All single byte instructions are converted automatically using a generic
+function which returns the index of the constructor. The index of the
+constructor is the byte value for all instructions. Added to this single byte
+value are the encoded parameters of the instruction. The last step of the
compilation is transforming the list of bytecode instructions to actual bytes.
\subsection{Helper functions}
-The \CI{ByteCode} type is just a boxed \gls{RWST} and that gives access to
-the whole range of \gls{RWST} functions. However, to apply a function the type
-must be unboxed. After application the type must be boxed again. To achieve
-this, several helper functions have been created. They are listed in
+Since the \CI{ByteCode} type is just a boxed \gls{RWST}, access to the whole
+range of \gls{RWST} functions is available. However, to use this, the type must
+be unboxed. After application the type must be boxed again. To achieve this,
+several helper functions have been created. They are given in
Listing~\ref{lst:helpers}. The \CI{op} and \CI{op2} functions is hand-crafted
to make operators that pop one or two values off the stack respectively. The
-\CI{tell`} is a wrapper around the \gls{RWST} function \CI{tell} that appends
-the argument to the \emph{Writer} value.
+\CI{tell`} function is a wrapper around the \gls{RWST} function \CI{tell} that
+appends the argument to the \emph{Writer} value.
\begin{lstlisting}[label={lst:helpers},caption={Some helper functions}]
op2 :: (ByteCode a p1) (ByteCode a p2) BC -> ByteCode b Expr
\subsection{Arithmetics \& Peripherals}
Almost all of the code from the simple classes exclusively use helper
-functions. Listing~\ref{lst:arithview} shows some implementations. The classes
-\CI{boolExpr} and the classes for the peripherals are implemented using the
-same strategy.
+functions. Listing~\ref{lst:arithview} shows some implementations. The
+\CI{boolExpr} class and the classes for the peripherals are implemented using
+the same strategy.
\begin{lstlisting}[label={lst:arithview},caption={%
Bytecode view implementation for arithmetic and peripheral classes}]
\subsection{Control Flow}
Implementing the sequence operator is very straightforward in the bytecode
-view. The function just sequences the two \glspl{RWST}. The \emph{If} statement
-requires some detailed explanation since labels come into play. The
-implementation speaks for itself in Listing~\ref{lst:controlflow}. First, all
-the labels are gathered after which they are placed in the correct order in the
-bytecode sequence. It can happen that multiple labels appear consecutively in
-the code. This is not a problem since the labels are resolved to real addresses
-later on anyway.
+view. The function just sequences the two \glspl{RWST}. The
+implementation for the \emph{If} statement speaks for itself in
+Listing~\ref{lst:controlflow}. First, all the labels are gathered after which
+they are placed in the correct order in the bytecode sequence. It can happen
+that multiple labels appear consecutively in the code. This is not a problem
+since the labels are resolved to real addresses later on anyway.
\begin{lstlisting}[label={lst:controlflow},%
caption={Bytecode view for \texttt{arith} class}]
noOp = tell` [BCNop]
\end{lstlisting}
-The semantics for the \glspl{mTask} bytecode view are different from the
-semantics for the \gls{C} view. \glspl{Task} in the \gls{C} view can start new
-\gls{Task} or themselves to continue, while in the bytecode view, \gls{Task}
-run idefinitly, one-shot or on interrupt. To allow interval and interrupt
-\glspl{Task} to terminate, a return instruction is added. This class was not
-available in the original system and is thus added. It just writes a single
-instruction so that the interpreter knows to stop execution.
+The semantics for the \gls{mTask}-\glspl{Task} bytecode view are different from
+the semantics of the \gls{C} view. \glspl{Task} in the \gls{C} view can start
+new \glspl{Task} or even start themselves to continue, while in the bytecode
+view, \glspl{Task} run indefinitly, one-shot or on interrupt. To allow interval
+and interrupt \glspl{Task} to terminate, a return instruction is added. This
+class was not available in the original system and is thus added. It just
+writes a single instruction so that the interpreter knows to stop execution.
Listing~\ref{lst:return} shows the classes and implementation for the return
expression.
addSDS sds v s = {s & sdss=[{sds & sdsval=BCValue v}:s.sdss]}
\end{lstlisting}
-All assignable types compile to a \gls{RWST} that writes one fetch instruction.
-For example, using a \gls{SDS} always results in an expression of the form
-\CI{sds \x=4 In ...}. The actual \CI{x} is the \gls{RWST} that always writes
-one \CI{BCSdsFetch} instruction with the correctly embedded \gls{SDS}.
-Assigning to an analog pin will result in the \gls{RWST} containing the
-\CI{BCAnalogRead} instruction. When the operation on the assignable is not a
-read operation from but an assign operation, the instruction(s) will be
-rewritten accordingly. This results in an \CI{BCSdsStore} or \CI{BCAnalogWrite}
+All assignable types compile to a \gls{RWST} which writes the specific fetch
+instruction(s). For example, using an \gls{SDS} always results in an expression
+of the form \CI{sds \x=4 In ...}. The actual \CI{x} is the \gls{RWST} that
+always writes one \CI{BCSdsFetch} instruction with the correctly embedded
+\gls{SDS}. Assigning to an analog pin will result in the \gls{RWST} containing
+the \CI{BCAnalogRead} instruction. When the operation on the assignable is not
+a read operation from but an assign operation, the instruction(s) will be
+rewritten accordingly. This results in a \CI{BCSdsStore} or \CI{BCAnalogWrite}
instruction respectively. The implementation for this is given in
Listing~\ref{lst:assignmentview}.
\subsection{Actual Compilation}
All the previous functions are tied together with the \CI{toMessages} function.
-This function compiles the bytecode and transforms the \gls{Task} in a message.
+This function compiles the bytecode and transforms the \gls{Task} to a message.
The \glspl{SDS} that were not already sent to the device are also added as
-messages to be sent to the device. This functionality is listed in
+messages to be sent to the device. This functionality is shown in
Listing~\ref{lst:compilation}. The compilation process consists of two steps.
First, the \gls{RWST} is executed. Then, the \emph{Jump} statements that
jump to labels are transformed to jump to program memory addresses. The
-translation of labels is possible in one sweep because no labels are reused.
+translation of labels is possible in one sweep because fresh labels are reused.
Reusing labels would not give a speed improvement since the labels are removed
-anyway in the end.
+in the end.
\begin{lstlisting}[label={lst:compilation},%
caption={Actual compilation.}]
\end{lstlisting}
\section{Examples}
-The heating example given previously in Listing~\ref{lst:exmtask} would be
+The thermostat example given previously in Listing~\ref{lst:exmtask} would be
compiled to the following code. The left column indicates the
position in the program memory.
repositories / msc-thesis1617.git / blobdiff