\begin{document}
\input{subfileprefix}
-\chapter{Edge device programming}%
-\label{chp:top4iot}
-\begin{chapterabstract}
- This chapter:
- \begin{itemize}
- \item shows how to create the \emph{Hello World!} application for microcontrollers using \gls{ARDUINO};
- \item extends this idea with multithreading, demonstrating the difficulty programming multi-tasking applications;
- \item describes a comparative variant in \gls{MTASK} and shows that upgrading to a multi-tasking variant is straightforward
- \item demonstrates that the complexity of running multiple tasks;
- \item and concludes with the history of \gls{MTASK}'s development.
- \end{itemize}
-\end{chapterabstract}
-
-The edge layer of \gls{IOT} system mostly consists of microcontrollers.
-Microcontrollers are tiny computers designed specifically for embedded applications.
-They therefore only have a soup\c{c}on of memory, have a slow processor, come with many energy efficient sleep modes and have a lot of peripheral support such as \gls{GPIO} pins.
-Usually, programming microcontrollers requires an elaborate multi-step toolchain of compilation, linkage, binary image creation, and burning this image onto the flash memory of the microcontroller in order to compile and run a program.
-The programs are usually cyclic executives instead of tasks running in an operating system, i.e.\ there is only a single task that continuously runs on the bare metal.
-\Cref{tbl:mcu_laptop} compares the hardware properties of a typical laptop with two very popular microcontrollers.
-
-\begin{table}
- \caption{Hardware characteristics of typical microcontrollers and laptops.}%
- \label{tbl:mcu_laptop}
- \begin{tabular}{llll}
- \toprule
- & Laptop & Atmega328P & ESP8266\\
- \midrule
- CPU speed & \qtyrange{2}{4}{\giga\hertz} & \qty{16}{\mega\hertz} & \qty{80}{\mega\hertz} or \qty{160}{\mega\hertz}\\
- \textnumero{} cores & \numrange{4}{8} & 1 & 1\\
- Storage & \qty{1}{\tebi\byte} & \qty{32}{\kibi\byte} & \qtyrange{0.5}{4}{\mebi\byte}\\
- \gls{RAM} & \qtyrange{4}{16}{\gibi\byte} & \qty{2}{\kibi\byte} & \qty{160}{\kibi\byte}\\
- Power & \qtyrange{50}{100}{\watt} & \qtyrange{0.13}{250}{\milli\watt} & \qtyrange{0.1}{350}{\milli\watt}\\
- Price & \euro{1500} & \euro{3} & \euro{4}\\
- \bottomrule
- \end{tabular}
-\end{table}
-
-Each type of microcontrollers comes with vendor-provided drivers, compilers and \glspl{RTS} but there are many platform that abstract away from this such as \gls{MBED} and \gls{ARDUINO} of which \gls{ARDUINO} is specifically designed for education and prototyping and hence used here.
-The popular \gls{ARDUINO} \gls{C}\slash\gls{CPP} dialect and accompanying libraries provide an abstraction layer for common microcontroller behaviour allowing the programmer to program multiple types of microcontrollers using a single language.
-Originally it was designed for the in-house developed open-source hardware with the same name but the setup allows porting to many architectures.
-It provides an \gls{IDE} and toolchain automation to perform all steps of the toolchain with a single command.
-
-\section{Hello world!}
-Traditionally, the first program that one writes when trying a new language is the so called \emph{Hello World!} program.
-This program has the single task of printing the text \emph{Hello World!} to the screen and exiting again, useful to become familiarised with the syntax and verify that the toolchain and runtime environment is working.
-On microcontrollers, there usually is no screen for displaying text.
-Nevertheless, almost always there is a built-in monochrome $1\times1$ pixel screen, namely \pgls{LED}.
-The \emph{Hello World!} equivalent on microcontrollers blinks this \gls{LED}.
-
-\Cref{lst:arduinoBlink} shows how the logic of a blink program might look when using \gls{ARDUINO}'s \gls{C}\slash\gls{CPP} dialect.
-Every \gls{ARDUINO} program contains a \arduinoinline{setup} and a \arduinoinline{loop} function.
-The \arduinoinline{setup} function is executed only once on boot, the \arduinoinline{loop} function is continuously called afterwards and contains the event loop.
-After setting the \gls{GPIO} pin to the correct mode, blink's \arduinoinline{loop} function alternates the state of the pin representing the \gls{LED} between \arduinoinline{HIGH} and \arduinoinline{LOW}, turning the \gls{LED} off and on respectively.
-In between it waits for \qty{500}{\ms} so that the blinking is actually visible for the human eye.
-
-Translating the traditional blink program to \gls{MTASK} can almost be done by simply substituting some syntax as seen in \cref{lst:blinkImp}.
-E.g.\ \arduinoinline{digitalWrite} becomes \cleaninline{writeD}, literals are prefixed with \cleaninline{lit} and the pin to blink is changed to represent the actual pin for the builtin \gls{LED} of the device used in the exercises.
-In contrast to the imperative \gls{CPP} dialect, \gls{MTASK} is a \gls{TOP} language and therefore there is no such thing as a loop, only task combinators to combine tasks.
-To simulate a loop, the \cleaninline{rpeat} task combinator can be used as this task combinator executes the argument task and, when stable, reinstates it.
-The body of the \cleaninline{rpeat} contains similarly named tasks to write to the pins and to wait in between.
-The tasks are connected using the sequential \cleaninline{>>|.} combinator that for all current intents and purposes executes the tasks after each other.
-
-\begin{figure}[ht]
- \begin{subfigure}[b]{.5\linewidth}
- \begin{lstArduino}[caption={Blink program.},label={lst:arduinoBlink}]
-void setup() {
- pinMode(D2, OUTPUT);
-}
-
-void loop() {
- digitalWrite(D2, HIGH);
- delay(500);
- digitalWrite(D2, LOW);
- delay(500);
-}
- \end{lstArduino}
- \end{subfigure}%
- \begin{subfigure}[b]{.5\linewidth}
- \begin{lstClean}[caption={Blink program.},label={lst:blinkImp}]
-blink :: Main (MTask v ()) | mtask v
-blink =
- declarePin D2 PMOutput \d2->
- {main = rpeat (
- writeD d2 true
- >>|. delay (lit 500)
- >>|. writeD d2 false
- >>|. delay (lit 500)
- )
-}
- \end{lstClean}
- \end{subfigure}
-\end{figure}
-
-\section{Threaded blinking}
-Now say that we want to blink multiple blinking patterns on different \glspl{LED} concurrently.
-For example, blink three \glspl{LED} connected to \gls{GPIO} pins $1,2$ and $3$ at intervals of \qtylist{500;300;800}{\ms}.
-Intuitively you want to lift the blinking behaviour to a function and call this function three times with different parameters as done in \cref{lst:blinkthreadno}
-
-\begin{lstArduino}[caption={Naive approach to multiple blinking patterns.},label={lst:blinkthreadno}]
-void setup () { ... }
-
-void blink (int pin, int wait) {
- digitalWrite(pin, HIGH);
- delay(wait);
- digitalWrite(pin, LOW);
- delay(wait);
-}
-
-void loop() {
- blink (D1, 500);
- blink (D2, 300);
- blink (D3, 800);
-}\end{lstArduino}
-
-Unfortunately, this does not work because the \arduinoinline{delay} function blocks all further execution.
-The resulting program will blink the \glspl{LED} after each other instead of at the same time.
-To overcome this, it is necessary to slice up the blinking behaviour in very small fragments so it can be manually interleaved \citep{feijs_multi-tasking_2013}.
-Listing~\ref{lst:blinkthread} shows how three different blinking patterns might be achieved in \gls{ARDUINO} using the slicing method.
-If we want the blink function to be a separate parametrizable function we need to explicitly provide all references to the required state.
-Furthermore, the \arduinoinline{delay} function can not be used and polling \arduinoinline{millis} is required.
-The \arduinoinline{millis} function returns the number of milliseconds that have passed since the boot of the microcontroller.
-Some devices use very little energy when in \arduinoinline{delay} or sleep state.
-Resulting in \arduinoinline{millis} potentially affects power consumption since the processor is basically busy looping all the time.
-In the simple case of blinking three \glspl{LED} on fixed intervals, it might be possible to calculate the delays in advance using static analysis and generate the appropriate \arduinoinline{delay} code.
-Unfortunately, this is very hard when for example the blinking patterns are determined at runtime.
-
-\begin{lstArduino}[label={lst:blinkthread},caption={Threading three blinking patterns.}]
-long led1 = 0, led2 = 0, led3 = 0;
-bool st1 = false, st2 = false, st3 = false;
-
-void blink(int pin, int dlay, long *lastrun, bool *st) {
- if (millis() - *lastrun > dlay) {
- digitalWrite(pin, *st = !*st);
- *lastrun += dlay;
- }
-}
-
-void loop() {
- blink(D1, 500, &led1, &st1);
- blink(D2, 300, &led2, &st1);
- blink(D3, 800, &led3, &st1);
-}\end{lstArduino}
-
-This method is very error prone, requires a lot of pointer juggling and generally results into spaghetti code.
-Furthermore, it is very difficult to represent dependencies between threads, often state machines have to be explicitly programmed by hand to achieve this.
-
-\section{Blinking in \texorpdfstring{\gls{MTASK}}{mTask}}
-The \cleaninline{delay} \emph{task} does not block the execution but \emph{just} emits no value when the target waiting time has not yet passed and emits a stable value when the time is met.
-In contrast, the \arduinoinline{delay()} \emph{function} on the \gls{ARDUINO} is blocking which prohibits interleaving.
-To make code reuse possible and make the implementation more intuitive, the blinking behaviour is lifted to a recursive function instead of using the imperative \cleaninline{rpeat} construct.
-The function is parametrized with the current state, the pin to blink and the waiting time.
-Creating recursive functions like this is not possible in the \gls{ARDUINO} language because the program would run out of stack in an instant and nothing can be interleaved.
-With a parallel combinator, tasks can be executed in an interleaved fashion.
-Therefore, blinking three different blinking patterns is as simple as combining the three calls to the \cleaninline{blink} function with their arguments as seen in \cref{lst:blinkthreadmtask}.
-
-% VimTeX: SynIgnore on
-\begin{lstClean}[label={lst:blinkthreadmtask},caption={Threaded blinking.}]
-blinktask :: MTask v () | mtask v
-blinktask =
- declarePin D1 PMOutput \d1->
- declarePin D2 PMOutput \d2->
- declarePin D3 PMOutput \d3->
- fun \blink=(\(st, pin, wait)->
- delay wait
- >>|. writeD d13 st
- >>|. blink (Not st, pin, wait)) In
- {main = blink (true, d1, lit 500)
- .||. blink (true, d2, lit 300)
- .||. blink (true, d3, lit 800)
- }\end{lstClean}
-% VimTeX: SynIgnore off
-
-\section{\texorpdfstring{\Gls{MTASK}}{MTask} history}
-\subsection{Generating \texorpdfstring{\gls{C}/\gls{CPP}}{C/C++} code}
-A first throw at a class-based shallowly \gls{EDSL} for microcontrollers was made by \citet{plasmeijer_shallow_2016}.
-The language was called \gls{ARDSL} and offered a type safe interface to \gls{ARDUINO} \gls{CPP} dialect.
-A \gls{CPP} code generation backend was available together with an \gls{ITASK} simulation backend.
-There was no support for tasks or even functions.
-Some time later in the 2015 \gls{CEFP} summer school, an extended version was created that allowed the creation of imperative tasks, \glspl{SDS} and the usage of functions \citep{koopman_type-safe_2019}.
-The name then changed from \gls{ARDSL} to \gls{MTASK}.
-
-\subsection{Integration with \texorpdfstring{\gls{ITASK}}{iTask}}
-\Citet{lubbers_task_2017} extended this in his Master's Thesis by adding integration with \gls{ITASK} and a bytecode compiler to the language.
-\Gls{SDS} in \gls{MTASK} could be accessed on the \gls{ITASK} server.
-In this way, entire \gls{IOT} systems could be programmed from a single source.
-However, this version used a simplified version of \gls{MTASK} without functions.
-This was later improved upon by creating a simplified interface where \glspl{SDS} from \gls{ITASK} could be used in \gls{MTASK} and the other way around \citep{lubbers_task_2018}.
-It was shown by \citet{amazonas_cabral_de_andrade_developing_2018} that it was possible to build real-life \gls{IOT} systems with this integration.
-Moreover, a course on the \gls{MTASK} simulator was provided at the 2018 \gls{CEFP}/\gls{3COWS} winter school in Ko\v{s}ice, Slovakia \citep{koopman_simulation_2018}.
-
-\section{Transition to \texorpdfstring{\gls{TOP}}{TOP}}
-The \gls{MTASK} language as it is now was introduced in 2018 \citep{koopman_task-based_2018}.
-This paper updated the language to support functions, tasks and \glspl{SDS} but still compiled to \gls{CPP} \gls{ARDUINO} code.
-Later the bytecode compiler and \gls{ITASK} integration was added to the language \citep{lubbers_interpreting_2019}.
-Moreover, it was shown that it is very intuitive to write microcontroller applications in a \gls{TOP} language \citep{lubbers_multitasking_2019}.
-One reason for this is that a lot of design patterns that are difficult using standard means are for free in \gls{TOP} (e.g.\ multithreading).
-In 2019, the \gls{CEFP} summer school in Budapest, Hungary hosted a course on developing \gls{IOT} applications with \gls{MTASK} as well \citep{lubbers_writing_2019}.
-
-\subsection{\texorpdfstring{\Glsxtrshort{TOP}}{TOP}}
-In 2022, the SusTrainable summer school in Rijeka, Croatia hosted a course on developing greener \gls{IOT} applications using \gls{MTASK} as well (the lecture notes are to be written).
-Several students worked on extending \gls{MTASK} with many useful features:
-\Citet{veen_van_der_mutable_2020} did preliminary work on a green computer analysis, built a simulator and explored the possibilities for adding bounded datatypes; \citet{boer_de_secure_2020} investigated the possibilities for secure communication channels; and \citet{crooijmans_reducing_2021} added abstractions for low-power operation to \gls{MTASK} such as hardware interrupts and power efficient scheduling (resulting in a paper as well \citet{crooijmans_reducing_2022}).
-\Citet{antonova_mtask_2022} defined a preliminary formal semantics for a subset of \gls{MTASK}.
-Moreover, plans for student projects and improvements include exploring integrating \gls{TINYML} into \gls{MTASK}; and adding intermittent computing support to \gls{MTASK}.
-
-In 2023, the SusTrainable summer school in Coimbra, Portugal will host a course on \gls{MTASK} as well.
-
-\subsection{\texorpdfstring{\gls{MTASK}}{mTask} in practise}
-Funded by the Radboud-Glasgow Collaboration Fund, collaborative work was executed with Phil Trinder, Jeremy Singer, and Adrian Ravi Kishore Ramsingh.
-An existing smart campus application was developed using \gls{MTASK} and quantitively and qualitatively compared to the original application that was developed using a traditional \gls{IOT} stack \citep{lubbers_tiered_2020}.
-This research was later extended to include a four-way comparison: \gls{PYTHON}, \gls{MICROPYTHON}, \gls{ITASK} and \gls{MTASK} \citep{lubbers_could_2022}.
-Currently, power efficiency behaviour of traditional versus \gls{TOP} \gls{IOT} stacks is being compared as well adding a \gls{FREERTOS} implementation to the mix as well.
-
-\chapter{The \texorpdfstring{\gls{MTASK}}{mTask} \texorpdfstring{\glsxtrshort{DSL}}{DSL}}%
-\label{chp:mtask_dsl}
-\begin{chapterabstract}
-This chapter introduces the \gls{MTASK} language more technically by:
- \begin{itemize}
- \item introducing the setup of the \gls{EDSL};
- \item and showing the language interface and examples for:
- \begin{itemize}
- \item data types
- \item expression
- \item task and their combinators.
- \end{itemize}
- \end{itemize}
-\end{chapterabstract}
-
-The \gls{MTASK} system is a complete \gls{TOP} programming environment for programming microcontrollers.
-It is implemented as an \gls{EDSL} in \gls{CLEAN} using class-based---or tagless-final---embedding (see \cref{sec:tagless-final_embedding}).
-
-Due to the nature of the embedding technique, it is possible to have multiple views on-programs written in the \gls{MTASK} language.
-The following interpretations are available for \gls{MTASK}.
-
-\begin{description}
- \item[Pretty printer]
-
- This interpretation converts the expression to a string representation.
- \item[Simulator]
-
- The simulator converts the expression to a ready-for-work \gls{ITASK} simulation in which the user can inspect and control the simulated peripherals and see the internal state of the tasks.
- \item[Byte code compiler]
-
- The compiler compiles the \gls{MTASK} program at runtime to a specialised byte code.
- Using a handful of integration functions and tasks, \gls{MTASK} tasks can be executed on microcontrollers and integrated in \gls{ITASK} as if they were regular \gls{ITASK} tasks.
- Furthermore, with special language constructs, \glspl{SDS} can be shared between \gls{MTASK} and \gls{ITASK} programs.
-\end{description}
-
-When using the compiler interpretation in conjunction with the \gls{ITASK} integration, \gls{MTASK} is a heterogeneous \gls{DSL}.
-I.e.\ some components---e.g.\ the \gls{RTS} on the microcontroller---is largely unaware of the other components in the system, and it is executed on a completely different architecture.
-The \gls{MTASK} language is an enriched simply-typed $\lambda$-calculus with support for some basic types, arithmetic operations, and function definition; and a task language (see \cref{sec:top}).
-
-\section{Types}
-To leverage the type checker of the host language, types in the \gls{MTASK} language are expressed as types in the host language, to make the language type safe.
-However, not all types in the host language are suitable for microcontrollers that may only have \qty{2}{\kibi\byte} of \gls{RAM} so class constraints are therefore added to the \gls{DSL} functions.
-The most used class constraint is the \cleaninline{type} class collection containing functions for serialization, printing, \gls{ITASK} constraints, \etc.
-Many of these functions can be derived using generic programming.
-An even stronger restriction on types is defined for types that have a stack representation.
-This \cleaninline{basicType} class has instances for many \gls{CLEAN} basic types such as \cleaninline{Int}, \cleaninline{Real} and \cleaninline{Bool}.
-The class constraints for values in \gls{MTASK} are omnipresent in all functions and therefore often omitted throughout throughout the chapters for brevity and clarity.
-
-\begin{table}[ht]
- \centering
- \caption{Mapping from \gls{CLEAN}/\gls{MTASK} data types to \gls{CPP} datatypes.}%
- \label{tbl:mtask-c-datatypes}
- \begin{tabular}{lll}
- \toprule
- \gls{CLEAN}/\gls{MTASK} & \gls{CPP} type & \textnumero{}bits\\
- \midrule
- \cleaninline{Bool} & \cinline{bool} & 16\\
- \cleaninline{Char} & \cinline{char} & 16\\
- \cleaninline{Int} & \cinline{int16_t} & 16\\
- \cleaninline{:: Long} & \cinline{int32_t} & 32\\
- \cleaninline{Real} & \cinline{float} & 32\\
- \cleaninline{:: T = A \| B \| C} & \cinline{enum} & 16\\
- \bottomrule
- \end{tabular}
-\end{table}
-
-\Cref{lst:constraints} contains the definitions for the auxiliary types and type constraints (such as \cleaninline{type} an \cleaninline{basicType}) that are used to construct \gls{MTASK} expressions.
-The \gls{MTASK} language interface consists of a core collection of type classes bundled in the type class \cleaninline{class mtask}.
-Every interpretation implements the type classes in the \cleaninline{mtask} class
-There are also \gls{MTASK} extensions that not every interpretation implements such as peripherals and \gls{ITASK} integration.
-\begin{lstClean}[caption={Classes and class collections for the \gls{MTASK} language.},label={lst:constraints}]
-class type t | iTask, ... ,fromByteCode, toByteCode t
-class basicType t | type t where ...
-
-class mtask v | expr, ..., int, real, long v
-
-\end{lstClean}
-
-Sensors, \glspl{SDS}, functions, \etc{} may only be defined at the top level.
-The \cleaninline{Main} type is used that is used to distinguish the top level from the main expression.
-Some top level definitions, such as functions, are defined using \gls{HOAS}.
-To make their syntax friendlier, the \cleaninline{In} type---an infix tuple---is used to combine these top level definitions as can be seen in \cleaninline{someTask} (\cref{lst:mtask_types}).
-
-\begin{lstClean}[caption={Example task and auxiliary types in the \gls{MTASK} language.},label={lst:mtask_types}]
-:: Main a = { main :: a }
-:: In a b = (In) infix 0 a b
-
-someTask :: MTask v Int | mtask v & liftsds v & sensor1 v & ...
-someTask =
- sensor1 config1 \sns1->
- sensor2 config2 \sns2->
- sds \s1=initial
- In liftsds \s2=someiTaskSDS
- In fun \fun1= ( ... )
- In fun \fun2= ( ... )
- In { main = mainexpr }
-\end{lstClean}
-
-\section{Expressions}\label{sec:expressions}
-\Cref{lst:expressions} shows the \cleaninline{expr} class containing the functionality to lift values from the host language to the \gls{MTASK} language (\cleaninline{lit}); perform number and boolean arithmetics; do comparisons; and conditional execution.
-For every common boolean and arithmetic operator in the host language, an \gls{MTASK} variant is present, suffixed by a period to not clash with \gls{CLEAN}'s builtin operators.
-
-\begin{lstClean}[caption={The \gls{MTASK} class for expressions},label={lst:expressions}]
-class expr v where
- lit :: t -> v t | type t
- (+.) infixl 6 :: (v t) (v t) -> v t | basicType, +, zero t
- ...
- (&.) infixr 3 :: (v Bool) (v Bool) -> v Bool
- (|.) infixr 2 :: (v Bool) (v Bool) -> v Bool
- Not :: (v Bool) -> v Bool
- (==.) infix 4 :: (v a) (v a) -> v Bool | Eq, basicType a
- ...
- If :: (v Bool) (v t) (v t) -> v t | type t
-\end{lstClean}
-
-Conversion to-and-fro data types is available through the overloaded functions \cleaninline{int}, \cleaninline{long} and \cleaninline{real} that will convert the argument to the respective type similar to casting in \gls{C}.
-
-\begin{lstClean}[caption={Type conversion functions in \gls{MTASK}.}]
-class int v a :: (v a) -> v Int
-class real v a :: (v a) -> v Real
-class long v a :: (v a) -> v Long
-\end{lstClean}
-
-Values from the host language must be explicitly lifted to the \gls{MTASK} language using the \cleaninline{lit} function.
-For convenience, there are many lower-cased macro definitions for often used constants such as \cleaninline{true :== lit True}, \cleaninline{false :== lit False}, \etc.
-
-\Cref{lst:example_exprs} shows some examples of these expressions.
-Since they are only expressions, there is no need for a \cleaninline{Main}.
-\cleaninline{e0} defines the literal $42$, \cleaninline{e1} calculates the literal $42.0$ using real numbers.
-\cleaninline{e2} compares \cleaninline{e0} and \cleaninline{e1} as integers and if they are equal it returns the \cleaninline{e2}$/2$ and \cleaninline{e0} otherwise.
-
-\begin{lstClean}[label={lst:example_exprs},caption={Example \gls{MTASK} expressions.}]
-e0 :: v Int | expr v
-e0 = lit 42
-
-e1 :: v Real | expr v
-e1 = lit 38.0 + real (lit 4)
-
-e2 :: v Int | expr v
-e2 = if' (e0 ==. int e1)
- (int e1 /. lit 2) e0
-\end{lstClean}
-
-\Gls{MTASK} is shallowly embedded in \gls{CLEAN} and the terms are constructed at runtime.
-This means that \gls{MTASK} programs can also be tailor-made at runtime or constructed using \gls{CLEAN} functions maximising the linguistic reuse \citep{krishnamurthi_linguistic_2001}
-\cleaninline{approxEqual} in \cref{lst:example_macro} performs an approximate equality---albeit not taking into account all floating point pecularities---.
-When calling \cleaninline{approxEqual} in an \gls{MTASK} function, the resulting code is inlined.
-
-\begin{lstClean}[label={lst:example_macro},caption={Example linguistic reuse in the \gls{MTASK} language.}]
-approxEqual :: (v Real) (v Real) (v Real) -> v Real | expr v
-approxEqual x y eps = if' (x ==. y) true
- ( if' (x >. y)
- (y -. x < eps)
- (x -. y < eps)
- )
-\end{lstClean}
-
-\subsection{Data types}
-Most of \gls{CLEAN}'s basic types have been mapped on \gls{MTASK} types.
-However, it can be useful to have access to compound types as well.
-All types in \gls{MTASK} must have a fixed size representation on the stack so sum types are not (yet) supported.
-While it is possible to lift types using the \cleaninline{lit} function, you cannot do anything with the types besides passing them around but they are being produced by some parallel task combinators (see \cref{sssec:combinators_parallel}).
-To be able to use types as first class citizens, constructors and field selectors are required (see \cref{chp:first-class_datatypes}).
-\Cref{lst:tuple_exprs} shows the scaffolding for supporting tuples in \gls{MTASK}.
-Besides the constructors and field selectors, there is also a helper function available that transforms a function from a tuple of \gls{MTASK} expressions to an \gls{MTASK} expression of a tuple.
-Examples for using tuple can be found in \cref{sec:mtask_functions}.
-
-\begin{lstClean}[label={lst:tuple_exprs},caption={Tuple constructor and field selectors in \gls{MTASK}.}]
-class tupl v where
- tupl :: (v a) (v b) -> v (a, b) | type a & type b
- first :: (v (a, b)) -> v a | type a & type b
- second :: (v (a, b)) -> v b | type a & type b
-
- tupopen f :== \v->f (first v, second v)
-\end{lstClean}
-
-\subsection{Functions}\label{sec:mtask_functions}
-Adding functions to the language is achieved by type class to the \gls{DSL}.
-By using \gls{HOAS}, both the function definition and the calls to the function can be controlled by the \gls{DSL} \citep{pfenning_higher-order_1988,chlipala_parametric_2008}.
-The \gls{MTASK} only allows first-order functions and does not allow partial function application.
-This is restricted by using a multi-parameter type class where the first parameter represents the arguments and the second parameter the view.
-By providing a single instance per function arity instead of providing one instance for all functions and using tuples for the arguments this constraint can be enforced.
-Also, \gls{MTASK} only supports top-level functions which is enforced by the \cleaninline{Main} box.
-The definition of the type class and the instances for an example interpretation (\cleaninline{:: Inter}) are as follows:
-
-\begin{lstClean}[caption={Functions in \gls{MTASK}.}]
-class fun a v :: ((a -> v s) -> In (a -> v s) (Main (MTask v u)))
- -> Main (MTask v u)
-
-instance fun () Inter where ...
-instance fun (Inter a) Inter | type a where ...
-instance fun (Inter a, Inter b) Inter | type a, type b where ...
-instance fun (Inter a, Inter b, Inter c) Inter | type a, ... where ...
-...
-\end{lstClean}
-
-Deriving how to define and use functions from the type is quite the challenge even though the resulting syntax is made easier using the infix type \cleaninline{In}.
-\Cref{lst:function_examples} show the factorial function, a tail-call optimised factorial function and a function with zero arguments to demonstrate the syntax.
-Splitting out the function definition for each single arity means that that for every function arity and combination of arguments, a separate class constraint must be created.
-Many of the often used functions are already bundled in the \cleaninline{mtask} class constraint collection.
-\cleaninline{factorialtail} shows a manually added class constraint.
-Definiting zero arity functions is shown in the \cleaninline{zeroarity} expression.
-Finally, \cleaninline{swapTuple} shows an example of a tuple being swapped.
-
-% VimTeX: SynIgnore on
-\begin{lstClean}[label={lst:function_examples},caption={Function examples in \gls{MTASK}.}]
-factorial :: Main (v Int) | mtask v
-factorial =
- fun \fac=(\i->if' (i <. lit 1)
- (lit 1)
- (i *. fac (i -. lit 1)))
- In {main = fac (lit 5) }
-
-factorialtail :: Main (v Int) | mtask v & fun (v Int, v Int) v
-factorialtail =
- fun \facacc=(\(acc, i)->if' (i <. lit 1)
- acc
- (fac (acc *. i, i -. lit 1)))
- In fun \fac=(\i->facacc (lit 1, i))
- In {main = fac (lit 5) }
-
-zeroarity :: Main (v Int) | mtask v
-zeroarity =
- fun \fourtytwo=(\()->lit 42)
- In fun \add=(\(x, y)->x +. y)
- In {main = add (fourtytwo (), lit 9)}
-
-swapTuple :: Main (v (Int, Bool)) | mtask v
-swapTuple =
- fun \swap=(tupopen \(x, y)->tupl y x)
- In {main = swap (tupl true (lit 42)) }
-\end{lstClean}
-% VimTeX: SynIgnore off
-
-\section{Tasks and task combinators}\label{sec:top}
-\Gls{MTASK}'s task language can be divided into three categories, namely
-\begin{enumerate*}
- \item Basic tasks, in most \gls{TOP} systems, the basic tasks are called editors, modelling the interactivity with the user.
- In \gls{MTASK}, there are no \emph{editors} in that sense but there is interaction with the outside world through microcontroller peripherals such as sensors and actuators.
- \item Task combinators provide a way of describing the workflow.
- They combine one or more tasks into a compound task.
- \item \glspl{SDS} in \gls{MTASK} can be seen as references to data that can be shared using many-to-many communication and are only accessible from within the task language to ensure atomicity.
-\end{enumerate*}
-
-As \gls{MTASK} is integrated with \gls{ITASK}, the same stability distinction is made for task values.
-A task in \gls{MTASK} is denoted by the \gls{DSL} type synonym shown in \cref{lst:task_type}.
-
-\begin{lstClean}[label={lst:task_type},caption={Task type in \gls{MTASK}.}]
-:: MTask v a :== v (TaskValue a)
-:: TaskValue a
- = NoValue
- | Value a Bool
-\end{lstClean}
-
-\subsection{Basic tasks}
-The most rudimentary basic tasks are the \cleaninline{rtrn} and \cleaninline{unstable} tasks.
-They lift the value from the \gls{MTASK} expression language to the task domain either as a stable value or an unstable value.
-There is also a special type of basic task for delaying execution.
-The \cleaninline{delay} task---given a number of milliseconds---yields an unstable value while the time has not passed.
-Once the specified time has passed, the time it overshot the planned time is yielded as a stable task value.
-See \cref{sec:repeat} for an example task using \cleaninline{delay}.
-
-\begin{lstClean}[label={lst:basic_tasks},caption={Function examples in \gls{MTASK}.}]
-class rtrn v :: (v t) -> MTask v t
-class unstable v :: (v t) -> MTask v t
-class delay v :: (v n) -> MTask v n | long v n
-\end{lstClean}
-
-\subsubsection{Peripherals}\label{sssec:peripherals}
-For every sensor or actuator, basic tasks are available that allow interaction with the specific peripheral.
-The type classes for these tasks are not included in the \cleaninline{mtask} class collection as not all devices nor all language interpretations have such peripherals connected.
-%\todo{Historically, peripheral support has been added \emph{by need}.}
-
-\Cref{lst:dht,lst:gpio} show the type classes for \glspl{DHT} sensors and \gls{GPIO} access.
-Other peripherals have similar interfaces, they are available in the \cref{sec:aux_peripherals}.
-For the \gls{DHT} sensor there are two basic tasks, \cleaninline{temperature} and \cleaninline{humidity}, that---will given a \cleaninline{DHT} object---produce a task that yields the observed temperature in \unit{\celcius} or relative humidity as a percentage as an unstable value.
-Currently, two different types of \gls{DHT} sensors are supported, the \emph{DHT} family of sensors connect through $1$-wire protocol and the \emph{SHT} family of sensors connected using \gls{I2C} protocol.
-Creating such a \cleaninline{DHT} object is very similar to creating functions in \gls{MTASK} and uses \gls{HOAS} to make it type safe.
-
-\begin{lstClean}[label={lst:dht},caption{The \gls{MTASK} interface for \glspl{DHT} sensors.}]
-:: DHT //abstract
-:: DHTInfo
- = DHT_DHT Pin DHTtype
- | DHT_SHT I2CAddr
-:: DHTtype = DHT11 | DHT21 | DHT22
-class dht v where
- DHT :: DHTInfo ((v DHT) -> Main (v b)) -> Main (v b) | type b
- temperature :: (v DHT) -> MTask v Real
- humidity :: (v DHT) -> MTask v Real
-
-measureTemp :: Main (MTask v Real) | mtask v & dht v
-measureTemp = DHT (DHT_SHT (i2c 0x36)) \dht->
- {main=temperature dht}
-\end{lstClean}
-
-\Gls{GPIO} access is divided into three classes: analog, digital and pin modes.
-For all pins and pin modes an \gls{ADT} is available that enumerates the pins.
-The analog \gls{GPIO} pins of a microcontroller are connected to an \gls{ADC} that translates the voltage to an integer.
-Analog \gls{GPIO} pins can be either read or written to.
-Digital \gls{GPIO} pins only report a high or a low value.
-The type class definition is a bit more complex since analog \gls{GPIO} pins can be used as digital \gls{GPIO} pins as well.
-Therefore, if the \cleaninline{p} type implements the \cleaninline{pin} class---i.e.\ either \cleaninline{APin} or \cleaninline{DPin}---the \cleaninline{dio} class can be used.
-\Gls{GPIO} pins usually operate according to a certain pin mode that states whether the pin acts as an input pin, an input with an internal pull-up resistor or an output pin.
-This setting can be applied using the \cleaninline{pinMode} class by hand or by using the \cleaninline{declarePin} \gls{GPIO} pin constructor.
-Setting the pin mode is a task that immediately finisheds and fields a stable unit value.
-Writing to a pin is also a task that immediately finishes but yields the written value instead.
-Reading a pin is a task that yields an unstable value---i.e.\ the value read from the actual pin.
-
-\begin{lstClean}[label={lst:gpio},caption={The \gls{MTASK} interface for \gls{GPIO} access.}]
-:: APin = A0 | A1 | A2 | A3 | A4 | A5
-:: DPin = D0 | D1 | D2 | D3 | D4 | D5 | D6 | D7 | D8 | D9 | D10 | D11 | D12 | D13
-:: PinMode = PMInput | PMOutput | PMInputPullup
-:: Pin = AnalogPin APin | DigitalPin DPin
-class pin p :: p -> Pin
-
-class aio v where
- writeA :: (v APin) (v Int) -> MTask v Int
- readA :: (v APin) -> MTask v Int
-
-class dio p v | pin p where
- writeD :: (v p) (v Bool) -> MTask v Bool
- readD :: (v p) -> MTask v Bool | pin p
-
-class pinMode v where
- pinMode :: (v PinMode) (v p) -> MTask v () | pin p
- declarePin :: p PinMode ((v p) -> Main (v a)) -> Main (v a) | pin p
-\end{lstClean}
-
-\begin{lstClean}[label={lst:gpio_examples},caption={\Gls{GPIO} example in \gls{MTASK}.}]
-task1 :: MTask v Int | mtask v
-task1 = declarePin A3 PMInput \a3->{main=readA a3}
+%\chapter{\texorpdfstring{\Glsxtrshort{TOP} for the \glsxtrshort{IOT}}{TOP for the IoT}}%
+\subfile{4iot}
-task2 :: MTask v Int | mtask v
-task2 = declarePin D3 PMOutput \d3->{main=writeD d3 true}
-\end{lstClean}
-
-\subsection{Task combinators}
-Task combinators are used to combine multiple tasks into one to describe workflows.
-There are three main types of task combinators, namely:
-\begin{enumerate*}
- \item Sequential combinators that execute tasks one after the other, possibly using the result of the left hand side.
- \item Parallel combinators that execute tasks at the same time combining the result.
- \item Miscellaneous combinators that change the semantics of a task---e.g.\ repeat it or delay execution.
-\end{enumerate*}
-
-\subsubsection{Sequential}
-Sequential task combination allows the right-hand side task to observe the left-hand side task value.
-All seqential task combinators are expressed in the \cleaninline{expr} class and can be---and are by default---derived from the Swiss army knife step combinator \cleaninline{>>*.}.
-This combinator has a single task on the left-hand side and a list of \emph{task continuations} on the right-hand side.
-The list of task continuations is checked every rewrite step and if one of the predicates matches, the task continues with the result of this combination.
-\cleaninline{>>=.} is a shorthand for the bind operation, if the left-hand side is stable, the right-hand side function is called to produce a new task.
-\cleaninline{>>|.} is a shorthand for the sequence operation, if the left-hand side is stable, it continues with the right-hand side task.
-The \cleaninline{>>~.} and \cleaninline{>>..} combinators are variants of the ones above that ignore the stability and continue on an unstable value as well.
-
-\begin{lstClean}[label={lst:mtask_sequential},caption={Sequential task combinators in \gls{MTASK}.}]
-class step v | expr v where
- (>>*.) infixl 1 :: (MTask v t) [Step v t u] -> MTask v u
- (>>=.) infixl 0 :: (MTask v t) ((v t) -> MTask v u) -> MTask v u
- (>>|.) infixl 0 :: (MTask v t) (MTask v u) -> MTask v u
- (>>~.) infixl 0 :: (MTask v t) ((v t) -> MTask v u) -> MTask v u
- (>>..) infixl 0 :: (MTask v t) (MTask v u) -> MTask v u
-
-:: Step v t u
- = IfValue ((v t) -> v Bool) ((v t) -> MTask v u)
- | IfStable ((v t) -> v Bool) ((v t) -> MTask v u)
- | IfUnstable ((v t) -> v Bool) ((v t) -> MTask v u)
- | Always (MTask v u)
-\end{lstClean}
-
-\todo{more examples step?}
-
-The following listing shows an example of a step in action.
-The \cleaninline{readPinBin} function produces an \gls{MTASK} task that classifies the value of an analogue pin into four bins.
-It also shows that the nature of embedding allows the host language to be used as a macro language.
-Furthermore
-
-\begin{lstClean}[label={lst:mtask_readpinbin},caption={Read an analog pin and bin the value in \gls{MTASK}.}]
-readPinBin :: Int -> Main (MTask v Int) | mtask v
-readPinBin lim = declarePin PMInput A2 \a2->
- { main = readA a2 >>*.
- [ IfValue (\x->x <. lim) (\_->rtrn (lit bin))
- \\ lim <-[64,128,192,256]
- & bin <- [0..]]}
-\end{lstClean}
-
-\subsubsection{Parallel}\label{sssec:combinators_parallel}
-The result of a parallel task combination is a compound that actually executes the tasks at the same time.
-
-There are two types of parallel task combinators (see \cref{lst:mtask_parallel}).
-The conjunction combinator (\cleaninline{.&&.}) combines the result by putting the values from both sides in a tuple.
-The stability of the task depends on the stability of both children.
-If both children are stable, the result is stable, otherwise the result is unstable.
-The disjunction combinator (\cleaninline{.\|\|.}) combines the results by picking the leftmost, most stable task.
-The semantics are easily described using \gls{CLEAN} functions shown in \cref{lst:semantics_con,lst:semantics_dis}.
-
-\begin{figure}[ht]
- \centering
- \begin{subfigure}[t]{.5\textwidth}
- \begin{lstClean}[caption={Semantics of the\\conjunction combinator.},label={lst:semantics_con}]
-con :: (TaskValue a) (TaskValue b)
- -> TaskValue (a, b)
-con NoValue r = NoValue
-con l NoValue = NoValue
-con (Value l ls) (Value r rs)
- = Value (l, r) (ls && rs)
-
- \end{lstClean}
- \end{subfigure}%
- \begin{subfigure}[t]{.5\textwidth}
- \begin{lstClean}[caption={Semantics of the\\disjunction combinator.},label={lst:semantics_dis}]
-dis :: (TaskValue a) (TaskValue a)
- -> TaskValue a
-dis NoValue r = r
-dis l NoValue = l
-dis (Value l ls) (Value r rs)
- | rs = Value r True
- | otherwise = Value l ls
- \end{lstClean}
- \end{subfigure}
-\end{figure}
-
-\begin{lstClean}[label={lst:mtask_parallel},caption={Parallel task combinators in \gls{MTASK}.}]
-class (.&&.) infixr 4 v :: (MTask v a) (MTask v b) -> MTask v (a, b)
-class (.||.) infixr 3 v :: (MTask v a) (MTask v a) -> MTask v a
-\end{lstClean}
-
-\Cref{lst:mtask_parallel_example} gives an example of the parallel task combinator.
-This program will read two pins at the same time, returning when one of the pins becomes \arduinoinline{HIGH}.
-If the combinator was the \cleaninline{.&&.} instead, the type would be \cleaninline{MTask v (Bool, Bool)} and the task would only return when both pins have been \arduinoinline{HIGH} but not necessarily at the same time.
-
-\begin{lstClean}[label={lst:mtask_parallel_example},caption={Parallel task combinator example in \gls{MTASK}.}]
-task :: MTask v Bool
-task =
- declarePin D0 PMInput \d0->
- declarePin D1 PMInput \d1->
- let monitor pin = readD pin >>*. [IfValue (\x->x) \x->rtrn x]
- In {main = monitor d0 .||. monitor d1}
-\end{lstClean}
-
-\subsubsection{Repeat}\label{sec:repeat}
-The \cleaninline{rpeat} combinator executes the child task.
-If a stable value is observed, the task is reinstated.
-The functionality of \cleaninline{rpeat} can also be simulated by using functions and sequential task combinators and even made to be stateful as can be seen in \cref{lst:blinkthreadmtask}.
-
-\begin{lstClean}[label={lst:mtask_repeat},caption={Repeat task combinators in \gls{MTASK}.}]
-class rpeat v where
- rpeat :: (MTask v a) -> MTask v a
-\end{lstClean}
-
-To demonstrate the combinator, \cref{lst:mtask_repeat_example} show \cleaninline{rpeat} in use.
-This task will mirror the value read from analog \gls{GPIO} pin \cleaninline{A1} to pin \cleaninline{A2} by constantly reading the pin and writing the result.
-
-\begin{lstClean}[label={lst:mtask_repeat_example},caption={Exemplatory repeat task in \gls{MTASK}.}]
-task :: MTask v Int | mtask v
-task =
- declarePin A1 PMInput \a1->
- declarePin A2 PMOutput \a2->
- {main = rpeat (readA a1 >>~. writeA a2 >>|. delay (lit 1000))}
-\end{lstClean}
-
-\subsection{\texorpdfstring{\Glsxtrlongpl{SDS}}{Shared data sources}}
-\Glspl{SDS} in \gls{MTASK} are by default references to shared memory but can also be references to \glspl{SDS} in \gls{ITASK} (see \cref{sec:liftsds}).
-Similar to peripherals (see \cref{sssec:peripherals}), they are constructed at the top level and are accessed through interaction tasks.
-The \cleaninline{getSds} task yields the current value of the \gls{SDS} as an unstable value.
-This behaviour is similar to the \cleaninline{watch} task in \gls{ITASK}.
-Writing a new value to \pgls{SDS} is done using \cleaninline{setSds}.
-This task yields the written value as a stable result after it is done writing.
-Getting and immediately after setting \pgls{SDS} is not necessarily an \emph{atomic} operation in \gls{MTASK} because it is possible that another task accesses the \gls{SDS} in between.
-To circumvent this issue, \cleaninline{updSds} is created, this task atomically updates the value of the \gls{SDS}.
-The \cleaninline{updSds} task only guarantees atomicity within \gls{MTASK}.
-
-\begin{lstClean}[label={lst:mtask_sds},caption={\Glspl{SDS} in \gls{MTASK}.}]
-:: Sds a // abstract
-class sds v where
- sds :: ((v (Sds t)) -> In t (Main (MTask v u))) -> Main (MTask v u)
- getSds :: (v (Sds t)) -> MTask v t
- setSds :: (v (Sds t)) (v t) -> MTask v t
- updSds :: (v (Sds t)) ((v t) -> v t) -> MTask v t
-\end{lstClean}
-
-\Cref{lst:mtask_sds_examples} shows an example using \glspl{SDS}.
-The \cleaninline{count} function takes a pin and returns a task that counts the number of times the pin is observed as high by incrementing the \cleaninline{share} \gls{SDS}.
-In the \cleaninline{main} expression, this function is called twice and the results are combined using the parallel or combinator (\cleaninline{.||.}).
-Using a sequence of \cleaninline{getSds} and \cleaninline{setSds} would be unsafe here because the other branch might write their old increment value immediately after writing, effectively missing a count.\todo{beter opschrijven}
-
-\begin{lstClean}[label={lst:mtask_sds_examples},caption={Examples with \glspl{SDS} in \gls{MTASK}.}]
-task :: MTask v Int | mtask v
-task = declarePin D3 PMInput \d3->
- declarePin D5 PMInput \d5->
- sds \share=0
- In fun \count=(\pin->
- readD pin
- >>* [IfValue (\x->x) (\_->updSds (\x->x +. lit 1) share)]
- >>| delay (lit 100) // debounce
- >>| count pin)
- In {main=count d3 .||. count d5}
-\end{lstClean}
+%\chapter{The \texorpdfstring{\gls{MTASK}}{mTask} \texorpdfstring{\glsxtrshort{DSL}}{DSL}}%
+\subfile{lang}
\chapter{Integration with \texorpdfstring{\gls{ITASK}}{iTask}}%
\label{chp:integration_with_itask}
\section{Integration with \texorpdfstring{\gls{ITASK}}{iTask}}
IFL18 paper stukken
+% Green computing
\subfile{green}
\input{subfilepostamble}
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