-\section{Conclusion}
-This thesis introduces a new view for the existing \gls{mTask}-\gls{EDSL}.
-The new view for the \gls{EDSL} compiles the language in to bytecode that can
-be interpreted by an \gls{mTask}-client. Clients have been written for several
-microcontrollers and consumer architectures that can be connected through
-various means of communication such as serial, bluetooth, wifi and wired
-network communication. The bytecode on the devices is interpreted using a
-simple stack machine and provides the programmer interfaces to the peripherals.
-The semantics of the \glspl{mTask} tries to resemble the \gls{iTasks} semantics
-as close as possible.
-
-The host language has a very efficient compiler and code generator. Therefore,
-the \gls{mTask}-system is also relatively fast because the compilation of
-\glspl{mTask} is nothing more than running some functions in the host language.
-
-The dynamic nature allows the microcontroller to be programmed once and used
-many times. The program memory of microcontrollers often guarantees around
-$10.000$ write or upload cycles and therefore existing techniques such as
-generating \gls{C} code are not usable for dynamic \gls{Task} environments.
-The dynamic nature also allows the programmer to design fail-over mechanisms.
-When a device is assigned a \gls{Task} but another device suddenly becomes
-unusable, the \gls{iTasks} system can reassign a new \gls{mTask}-\gls{Task} to
-the first device that possibly takes over some of the functionality of the
-broken device without needing to recompile the code.
-
-\section{Discussion}
-\todo{class based shallow doesn't have multiple backend support}
-\todo{slow client software because of intepretation}
-\todo{What happens if a device dies? Task resending, add to handshake}
-
-
-\section{Future Research}
-The system is still crude and a proof of concept. Improvements and extension
-for the system are amply available in several fields of study.
+\section{Discussion \& Future Research}
+The system is still a crude prototype and a proof of concept. Improvements and
+extension for the system are amply available in several fields of study.
\subsection{Simulation}
An additional simulation view to the \gls{mTask}-\gls{EDSL} could be added that
works in the same way as the existing \gls{C}-backed simulation. It simulates
the bytecode interpretation. Moreover would be possible to let the simulator
-function as real device. Thus handling all communication through the
+function as a real device, thus handling all communication through the
existing \gls{SDS}-based systems and behave like a real device. At the moment
the \emph{POSIX}-client is the reference client and contains debugging code.
Adding a simulation view to the system allows for easy interactive debugging.
However, it might not be easy to devise a simulation tool that accurately
simulates the \gls{mTask} system accurately on some levels. The semantics can
-be simulated but for example timing and peripheral input/output are more
-difficult to simulate properly.
+be simulated but timing and peripheral input/output are more difficult to
+simulate properly.
\subsection{Optimization}
True multitasking could be added to the client software. This allows
\gls{mTask}-\glspl{Task} to run truly parallel. All \glspl{mTask} get slices
of execution time and will each have their own interpreter state instead of one
system-wide one that is reset after am \gls{mTask} finishes. This does require
-separate stacks for each task and therefore increases the system requirements
-of the client software. However, it could be implemented as a compile-time
-option and exchanged during the handshake so that the server knows the
-multithreading capabilities of the client.
+separate stacks for each \gls{Task} and therefore increases the system
+requirements of the client software. However, it could be implemented as a
+compile-time option and exchanged during the handshake so that the server knows
+the multithreading capabilities of the client.
-\todo{Parametric lenses on devices share?}
+Hardly any work has been done in the interpreter. The current interpreter is a
+no nonsense stack machine. A lot of improvements can be done in this part. For
+example, precomputed \emph{gotos} can improve jumping to the correct part of
+the code corresponding to the correct instruction. Moreover, the stack
+currently consists of 16-bit values. All operations work on 16-bit values and
+this simplifies the interpreter implementation. A memory improvement can be
+made by converting the stack to 8-bit values. This does pose some problems
+since an equality instruction must work on single-byte booleans \emph{and}
+two-byte integers. Adding specialized instructions per word size could overcome
+this problem.
\subsection{Resources}
Resource analysis during compilation can be useful to determine if an
\gls{mTask}-\gls{Task} is suitable for a specific device. If the device does
-not contain the correct peripherals such as an \gls{LCD} then the
+not contain the correct peripherals --- such as an \gls{LCD} --- then the
\gls{mTask}-\gls{Task} should be rejected and feedback to the user must be
-given.
+given. It might even be possible to do this statically on the type level.
This idea could be extended to the analysis of stack size and possibly
communication bandwidth. With this functionality ever more reliable fail-over
-systems can be designed. When the system knows more precise bounds it can
+systems can be designed. When the system knows precise bounds it can
allocate more \glspl{Task} on a device whilst staying within safe memory
bounds. The resource allocation can be done at runtime within the backend
itself or a general backend can be devices that can calculate the resources
-needed for a given \gls{mTask}. A specific \gls{mTask} can not have multiple
+needed for a given \gls{mTask}. A specific \gls{mTask} cannot have multiple
views at the same time due to the restrictions of class based shallow
embedding. It might even be possible to encode the resource allocation in the
type system itself using forms of dependant types.
\subsection{Functionality}
-More task-combinators already existing in the \gls{iTasks}-system could be added
-to the \gls{mTask}-system to allow for more fine-grained control flow between
-\gls{mTask}-\glspl{Task}. In this way the new system follows the \gls{TOP}
-paradigm even more and makes programming \glspl{mTask} for
+More \gls{Task}-combinators --- already existing in the \gls{iTasks}-system ---
+could be added to the \gls{mTask}-system to allow for more fine-grained control
+flow between \gls{mTask}-\glspl{Task}. In this way the new system follows the
+\gls{TOP} paradigm even more and makes programming \glspl{mTask} for
\gls{TOP}-programmers more seamless. Some of the combinators require previously
mentioned extension such as the parallel combinator. Others might be achieved
using simple syntactic transformations.
-Currently the \gls{C}-view allows tasks to launch other tasks. In the current
-system this type of logic has to take place server side. Adding this
-functionality to the bytecode-view allows greater flexibility, easier
+Currently the \gls{C}-view allows \glspl{Task} to launch other \glspl{Task}. In
+the current system this type of logic has to take place server side. Adding
+this functionality to the bytecode-view allows greater flexibility, easier
programming and less communication resources. Adding these semantics requires
modifications to the client software and extensions to the communication
-protocol since relations between tasks also need to be encoded and
+protocol since relations between \glspl{Task} also need to be encoded and
communicated.
+
+\subsection{Robustness}
+The robustness of the system can be greatly improved. Devices that lose
+connection are in the current system not well supported. The device will stop
+functioning and have to be emptied for a reconnect. \Glspl{Task} residing on a
+device that disconnected should be kept on the server to allow a swift
+reconnect and restoration of the \glspl{Task}. This holds the same for the
+client software. The client drops all existing \glspl{Task} on a shutdown
+request. An extra specialization of the shutdown could be added that drops the
+connection but keeps the \glspl{Task} in memory. During the downtime the
+\glspl{Task} can still be executed but publications need to be delayed. If the
+same server connects to the client the delayed publications can be sent
+anyways.
+
+Moreover, devices could send their current \glspl{Task} back at the
+server to synchronize it. This allows interchanging servers without
+interrupting the client. Allowing the client to send \glspl{Task} to the server
+is something to handle with care because it can easily cause high bandwidth
+usage.
+
+\section{Conclusion}
+This thesis introduces a novel system for add \gls{IoT} functionality to
+the \gls{TOP} implementation \gls{iTasks}. A new view for the existing
+\gls{mTask}-\gls{EDSL} has been created which compiles the program
+into bytecode that can be interpreted by a client. Clients have
+been written for several microcontrollers and consumer architectures which can
+be connected through various means of communication such as serial port,
+bluetooth, wifi and wired network communication. The bytecode on the devices is
+interpreted using a stack machine and provides the programmer interfaces
+to the peripherals. The semantics of the \glspl{mTask} tries to resemble the
+\gls{iTasks} semantics as close as possible.
+
+The host language has a very efficient compiler and code generator. Therefore,
+compiling \glspl{mTask} is also fast. Compiling \glspl{mTask} is nothing
+more than running some functions native to the host language.
+
+The dynamic nature allows the microcontroller to be programmed once and used
+many times. The program memory of microcontrollers often guarantees around
+$10.000$ write or upload cycles and therefore existing techniques such as
+generating \gls{C} code are not usable for dynamic \gls{Task} environments.
+The dynamic nature also allows the programmer to design fail-over mechanisms.
+When a device is assigned a \gls{Task} but another device suddenly becomes
+unusable, the \gls{iTasks} system can reassign a new \gls{mTask}-\gls{Task} to
+the first device that possibly takes over some of the functionality of the
+broken device without needing to recompile the code.
repositories / msc-thesis1617.git / blobdiff