methods.tex

   1 \section{\acrlong{TOP}}
   2 \gls{TOP} is a recent new programming paradigm implemented as
   3 \gls{iTasks}~\cite{achten_introduction_2015} in
   4 the pure lazy functional language \gls{Clean}
   5
   6 \todo{Main terms}
   7 The lazy functional programming language based on graph rewriting
   8 \gls{Clean}~\cite{brus_cleanlanguage_1987}
   9
  10 \section{\acrlong{EDSL}s}
  11
  12 \section{Devices}
  13
  14 \subsection{Specification}
  15
  16 \subsection{Communication}
  17
  18
  19 \section{mTasks}
  20 \subsection{\gls{EDSL}}
  21
  22 \subsection{Shares}
  23 %\subsection{Serial port communication in Clean and iTasks}
  24 %In the first exploration stage I added duplex serial port communication to
  25 %iTasks in the same way as TCP is added. To make it work several changes had to
  26 %be done to the iTasks core to allow backgroundtasks to be added at runtime. The
  27 %function shown in Listing~\ref{lst:serialtask} results into a task that
  28 %sends the data added to the output queue through the serial port and adds data
  29 %received to the input queue for the user to process.
  30 %
  31 %\begin{lstlisting}[caption={Serial port communication in iTasks},
  32 %       language=Clean,label={lst:serialtask}]
  33 %syncSerialChannel :: String TTYSettings (Shared ([String],[String],Bool)) -> Task ()
  34 %
  35 %:: ByteSize = BytesizeFive | BytesizeSix | BytesizeSeven | BytesizeEight
  36 %:: Parity = ParityNone | ...ParityOdd | ParityEven | ParitySpace | ParityMark
  37 %:: BaudRate = ... | B9600 | B19200 | ...
  38 %:: TTYSettings = {
  39 %       baudrate :: BaudRate,
  40 %       bytesize :: ByteSize,
  41 %       parity :: Parity,
  42 %       stop2bits :: Bool,
  43 %       xonxoff :: Bool}
  44 %\end{lstlisting}
  45 %
  46 %\subsection{mTasks}
  47 %The core of the project revolves around the embedded domain specific language
  48 %(EDSL) called mTask designed by Pieter Koopman. mTasks is used to use the task
  49 %oriented programming on microcontrollers in a type-safe environment. Originally
  50 %mTasks are compiled to c code that could be compiled for arduino compatible
  51 %devices.  Such generated code will be flashed to the program memory once. In
  52 %short, the original mTask system is comparable to an entire iTasks sytem
  53 %including the engine.
  54 %
  55 %For this project the imperative language constructs of the mTask DSL are used.
  56 %Listing~\ref{lst:mtask} shows some of these class base DSL components for
  57 %things like arithmetics, sequencing, conditionals, shared data sources and
  58 %interaction with the user LEDs. Together with some helper functions code
  59 %programmed in this DSL can be compiled to bytecode and sent to a device.
  60 %
  61 %\begin{lstlisting}[language=Clean,label={lst:mtask},
  62 %       caption={Parts of the mTask DSL}]
  63 %:: Upd   = Upd
  64 %:: Expr  = Expr
  65 %:: Stmt  = Stmt
  66 %:: UserLED = LED1 | LED2 | LED3
  67 %
  68 %:: Main a = {main :: a}
  69 %
  70 %class arith v where
  71 %  lit :: t -> v t Expr | ...
  72 %  (+.) infixl 6 :: (v t p) (v t q) -> v t Expr | ...
  73 %class IF v where
  74 %  IF :: (v Bool p) (v t q) (v s r) -> v () Stmt | isExpr p
  75 %class sds v where
  76 %  sds :: ((v t Upd)->In t (Main (v c s))) -> (Main (v c s)) | ...
  77 %  pub :: (v t Upd) -> v t Expr | ...
  78 %class seq v where
  79 %  (:.) infixr 0 :: (v t p) (v u q) -> v u Stmt | ...
  80 %class assign v where
  81 %  (=.) infixr 2 :: (v t Upd) (v t p) -> v t Expr | ...
  82 %class noOp v where noOp :: v t p
  83 %class userLed v where
  84 %       ledOn :: UserLED -> (v () Stmt)
  85 %       ledOff :: UserLED -> (v () Stmt)
  86 %\end{lstlisting}
  87 %
  88 %\subsection{iTasks}
  89 %In iTasks several tasks have been devised to handle the communication. Moreover
  90 %the tasks will synchronize the shared data sources in the mTask domain with
  91 %real SDSs in the iTasks domain allowing for communication between mTasks and
  92 %iTasks tasks. To not clutter the communication channels the SDSs are not
  93 %synchronized on every change on the device. When a share changes on the server
  94 %his new value will be pushed to the device immediately. When a share is updated
  95 %on the client it must be explicitly published using. This approach has been
  96 %taken because some shares might be only used internally and therefore would
  97 %clutter the communication channels that could be low-bandwidth.
  98 %
  99 %
 100 %\subsection{Devices}
 101 %For the devices an engine has been built that can receive mTasks and SDSs and
 102 %execute them accordingly. To add a new device to the list the programmer just
 103 %has to implement a relatively small interface. All the other functionality is
 104 %using standard C or the interface. This interface is listed in~%
 105 %\ref{lst:interface} and includes reading and writing data, controlling the
 106 %peripherals and some auxiliary functions.
 107 %
 108 %\begin{lstlisting}[language=c,caption={Device interface},label={lst:interface}]
 109 %uint8_t read_byte(void);
 110 %void write_byte(uint8_t b);
 111 %
 112 %void write_dpin(uint8_t i, bool b);
 113 %bool read_dpin(uint8_t i);
 114 %
 115 %void write_apin(uint8_t i, uint8_t a);
 116 %uint8_t read_apin(uint8_t i);
 117 %
 118 %long millis(void);
 119 %bool input_available(void);
 120 %void delay(long ms);
 121 %
 122 %void setup(void);
 123 %void debug(char *fmt, ...);
 124 %void pdie(char *s);
 125 %void die(char *fmt, ...);
 126 %\end{lstlisting}
 127 %
 128 %mTasks run either at a fixed interval or are one-shot which is added to the
 129 %message. The entire protocol specification can be found in the code that is
 130 %available. When an mTask is one-shot it will only be executed once and then
 131 %removed. This can be useful for user related tasks such as shutting down blinds
 132 %or turning on lights for an indefinite time. mTasks that run at a fixed
 133 %interval time can be used to monitor sensors or to periodically communicate
 134 %with peripherals like LCD screens.
 135 %
 136 %There are many things to be improved upon in future research. Most likely these
 137 %points will be touched upon in my Master's thesis research.
 138 %\begin{itemize}
 139 %       \item Support task combinators and functions.
 140 %
 141 %               The mTask language already supports the step combinator and it might be
 142 %               fruitful to add for more expressively. Moreover functions would also
 143 %               add a lot. They can be used to share code between tasks to reduce the
 144 %               bytecode size.
 145 %       \item Seamless integration with iTasks.
 146 %
 147 %               At the moment everything works but is hacked together. I would like to
 148 %               extend this with a more robust system that allows adding devices on the
 149 %               fly and adds functionality to monitor the mTask devices.
 150 %       \item Dynamic mTask/SDS allocation.
 151 %
 152 %               Currently all client data for mTask and SDS storage is statically
 153 %               allocated. This means that when only a few tasks are used the memory
 154 %               needed is too high. This can be improved upon by only allocating
 155 %               resources for tasks when they are requested and this would allow the
 156 %               system to run on low memory devices like arduino's.
 157 %       \item Extend on SDSs.
 158 %
 159 %               In the current system the shared data sources used in mTask programs
 160 %               live in a different domain and are synchronized with an iTask
 161 %               counterpart. Programming mTasks could be made more intuitive if you
 162 %               could use standard SDSs from iTasks. Moreover, at the moment only
 163 %               integer and boolean shares are allowed. This really should be extended
 164 %               to at least strings.
 165 %       \item Slicing tasks.
 166 %
 167 %               Every mTask runs in its entirety and to not run into race and
 168 %               scheduling problems loops are not allowed in the mTasks. An improvement
 169 %               to this could be multithreading the tasks by giving them slices of
 170 %               computation and pausing them every slice. In this way loops could be
 171 %               allowed without blocking the entire system. It does require more memory
 172 %               however.
 173 %       \item Run tasks when an interrupt fires.
 174 %
 175 %               Tasks can be scheduled either one-shot or at an interval. It might be
 176 %               useful to tie mTasks to hardware interrupts to increase responsiveness
 177 %               and possibly battery life. These interrupts do not need to be hardware
 178 %               based. A usecase might be to run a task when some other task is
 179 %               yielding a value (see task combinators) or to run a task when a shared
 180 %               data source is received from the server.
 181 %\end{itemize}