X-Git-Url: https://git.martlubbers.net/?a=blobdiff_plain;f=results.mtask.tex;h=c6adefb744f7d71e9b2dd47c6591be82751bc3b3;hb=36d2564cca6ffab6506198f13545e5d02cf2b5cc;hp=9580dec4917da66c9a8f29699ced1c31f8c60018;hpb=7b0fe8509016c0841d35239dc87150e945cfd960;p=msc-thesis1617.git diff --git a/results.mtask.tex b/results.mtask.tex index 9580dec..c6adefb 100644 --- a/results.mtask.tex +++ b/results.mtask.tex @@ -1,51 +1,107 @@ -Some functionality of the original \gls{mTask}-\gls{EDSL} will not be used in -this extension \gls{EDSL}. Conversely, some functionality needed was not -available in the existing \gls{EDSL}. Due to the nature of class based shallow -embedding this obstacle is very 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{Semantics} -\todo{semantics} - -\section{Bytecode compilation} -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 called \CI{ByteCode}. As shown in -Listing~\ref{lst:bcview}, the \CI{ByteCode} view is a boxed \gls{RWST} that -writes bytecode instructions (\CI{BC}) while carrying around a \CI{BCState}. -The state is kept between devices and contains fresh variable names and a -register of shares used. +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 +sense that the \gls{C}-view does. \Glspl{Task} used with the \gls{C}-view are a +main program that executes code and launches \glspl{Task}. It was also possible +to just have a main program. The current \gls{mTask}-system only supports main +programs. Sending a \gls{Task} always goes together with choosing a scheduling +strategy. This strategy can be one of the following three strategies as +reflected in the \CI{MTTask} message type. + +\begin{itemize} + \item\CI{OneShot} + + \CI{OneShot} takes no parameters and means that the \gls{Task} will run + once and will then be removed automatically. This type of scheduling + could be useful, for example, in retrieving sensor information on + request of a user. + \item\CI{OnInterval} + + \CI{OnInterval} has the number of milliseconds to wait in between + executions as a parameter. \Glspl{Task} running with this scheduling + method are executed at predetermined intervals. + \item\CI{OnInterrupt} + + The last scheduling method is running \glspl{Task} on a specific + 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 +\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. 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} +class. Therefore, an extra class is added that contains the extra +functionality. Programmers can choose to implement it for existing views in the +future but are not obliged to. The publication function has the following +signature: +\begin{lstlisting}[caption={The \texttt{sdspub} class}] +class sdspub v where + pub :: (v t Upd) -> v t Expr | type t +\end{lstlisting} + +\section{Bytecode compilation view}\label{sec:compiler} +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 +and is unique to a device. The state contains fresh variable names and a +register of \glspl{SDS} that are used. Types implementing the \gls{mTask} classes must have two free type variables. Therefore the \gls{RWST} is wrapped with a constructor and two phantom type variables are added. This means that the programmer has to unbox the -\CI{ByteCode} object to be able to use return values for the monad. Tailor made -access functions are used to achieve this with ease. The fresh variable stream -in a compiler using an \gls{RWST} is often put in to the \emph{Reader} part of -the monad. However, not all code is compiled immediately and later on the fresh -variable stream can not contain variables that were used before. Therefore this -information is put in the state which is kept between compilations. +\CI{ByteCode} object to be able to make use of the \gls{RWST} functionality +such as return values. Tailor made access functions are used to achieve this +with ease. The fresh variable stream in a compiler using a \gls{RWST} is often +put into the \emph{Reader} part of the monad. However, not all code is compiled +immediately and later on the fresh variable stream cannot contain variables +that were used before. Therefore this information is put in the state which is +kept between compilations. Not all types are suitable for usage in bytecode compiled programs. Every value used in the bytecode view must fit in the \CI{BCValue} type which restricts -the content. Most notably, the type must be bytecode encodable. A \CI{BCValue} +the content. Most notably, the type must be bytecode encodable. A \CI{BCValue} must be encodable and decodable without losing type or value information. At -the moment a simple encoding scheme is used that uses a single byte prefixes to -detect which type the value is. The devices know of these prefixes and act -accordingly. +the moment a simple encoding scheme is used that uses single byte prefixes to +detect the type of the value. The devices know these prefixes and can apply the +same detection if necessary. \begin{lstlisting}[label={lst:bcview},caption={Bytecode view}] :: ByteCode a p = BC (RWS () [BC] BCState ()) :: BCValue = E.e: BCValue e & mTaskType, TC e -:: BCShare = { - sdsi :: Int, - sdsval :: BCValue +:: BCShare = + { sdsi :: Int + , sdsval :: BCValue } -:: BCState = { - freshl :: [Int], - freshs :: [Int], - sdss :: [BCShare] +:: BCState = + { freshl :: Int + , freshs :: Int + , sdss :: [BCShare] } class toByteCode a :: a -> String @@ -60,18 +116,16 @@ instance arith ByteCode instance serial ByteCode \end{lstlisting} -\section{Implementation} -\subsection{Instruction Set} +\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 for the lowest -program size. +kept large, but under $255$, to get as much expressieve power as possible while +keeping all instruction within one byte. -The interpreter is a -stack machine. Therefore the it needs instructions like \emph{Push} and -\emph{Pop}. The virtual instruction \CI{BCLab} is added to allow for an easy -implementation. However, this is not a real instruction and the labels are -resolved to actual addresses in the final step of compilation to save -instructions. +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. +However, this is not a real instruction and the labels are resolved to actual +program memory addresses in the final step of compilation to save instructions +and avoid label lookups at runtime. \begin{lstlisting}[label={bc:instr},% caption={Bytecode instruction set}] @@ -99,27 +153,27 @@ instructions. | BCReturn \end{lstlisting} -All instructions are can be converted semi-automatically using the generic -function \CI{consIndex\{*\}} that gives the index of the constructor. This -constructor index is the actual byte value for the instruction. The -\CI{BCValue} type contains existentially quantified types and therefore must -have a given implementation for all generic functions. +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 us 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 some helper functions have been created. They are listed in -Listing~\ref{lst:helpers}. The \CI{op} and \CI{op2} function is 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. +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`} 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 op2 (BC x) (BC y) bc = BC (x >>| y >>| tell [bc]) -op :: (ByteCode a p) BC -> ByteCode a Expr +op :: (ByteCode a p) BC -> ByteCode b c op (BC x) bc = BC (x >>| tell [bc]) tell` :: [BC] -> (ByteCode a p) @@ -130,10 +184,10 @@ unBC (BC x) = x \end{lstlisting} \subsection{Arithmetics \& Peripherals} -Almost all of the code from the simple classes use exclusively helper -functions. Listing~\ref{lst:arithview} shows some implementations. The classes -\CI{boolExpr} and the classes for the peripherals are implemented in the same -fashion. +Almost all of the code from the simple classes exclusively use helper +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}] @@ -148,39 +202,89 @@ instance userLed ByteCode where \end{lstlisting} \subsection{Control Flow} +Implementing the sequence operator is very straightforward in the bytecode +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}}] + caption={Bytecode view for \texttt{arith} class}] +freshlabel = get >>= \st=:{freshl}->put {st & freshl=freshl+1} >>| pure freshl + +instance If ByteCode Stmt Stmt Stmt where If b t e = BCIfStmt b t e +instance If ByteCode e Stmt Stmt where If b t e = BCIfStmt b t e +instance If ByteCode Stmt e Stmt where If b t e = BCIfStmt b t e +instance If ByteCode x y Stmt where If b t e = BCIfStmt b t e +instance IF ByteCode where + IF b t e = BCIfStmt b t e + (?) b t = BCIfStmt b t (tell` []) +BCIfStmt (BC b) (BC t) (BC e) = BC ( + freshlabel >>= \else->freshlabel >>= \endif-> + b >>| tell [BCJmpF else] >>| + t >>| tell [BCJmp endif, BCLab else] >>| + e >>| tell [BCLab endif] + ) + instance noOp ByteCode where noOp = tell` [BCNop] \end{lstlisting} +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. + +\begin{lstlisting}[label={lst:return},% + caption={Bytecode view for the return instruction}] +class retrn v where + retrn :: v () Expr + +instance retrn ByteCode where + retrn = tell` [BCReturn] +\end{lstlisting} + \subsection{Shared Data Sources \& Assignment} -Shared data sources must be acquired from the state and constructing one -happens via multiple steps. First a fresh identifier is grabbed from the state. -Then a \CI{BCShare} record is created with that identifier. A \CI{BCSdsFetch} -instruction is written and the body is generated to finally add the share to -the actual state. The exact implementation is shown in -Listing~\ref{lst:shareview}. +Fresh \gls{SDS} are generated using the state and constructing one involves +multiple steps. First, a fresh identifier is grabbed from the state. Then a +\CI{BCShare} record is created with that identifier. A \CI{BCSdsFetch} +instruction is written and the body is generated to finally add the \gls{SDS} +to the actual state with the value obtained from the function. The exact +implementation is shown in Listing~\ref{lst:shareview}. \begin{lstlisting}[label={lst:shareview},% caption={Bytecode view for \texttt{arith}}] +freshshare = get >>= \st=:{freshs}->put {st & freshs=freshs+1} >>| pure freshs + instance sds ByteCode where - sds f = {main = BC (freshs - >>= \sdsi->pure {BCShare | sdsi=sdsi,sdsval=BCValue 0} - >>= \sds->pure (f (tell` [BCSdsFetch sds])) - >>= \(v In bdy)->modify (addSDS sds v) - >>| unBC (unMain bdy))} + sds f = {main = BC (freshshare + >>= \sdsi->pure {BCShare|sdsi=sdsi,sdsval=BCValue 0} + >>= \sds->pure (f (tell` [BCSdsFetch sds])) + >>= \(v In bdy)->modify (addSDS sds v) + >>| unBC (unMain bdy)) + } +instance sdspub ByteCode where pub (BC x) = BC (censor (\[BCSdsFetch s]->[BCSdsPublish s]) x) addSDS sds v s = {s & sdss=[{sds & sdsval=BCValue v}:s.sdss]} \end{lstlisting} -All assignable types compile to an \gls{RWST} that writes one instruction. 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 correct \gls{SDS} embedded. When the -call of the \CI{x} is not a read but an assignment, the instruction will be -rewritten as a \CI{BCSdsStore}. The implementation for this is given in +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}. \begin{lstlisting}[label={lst:assignmentview},% @@ -193,5 +297,57 @@ makeStore [BCDigitalRead i] = [BCDigitalWrite i] makeStore [...] = [...] \end{lstlisting} -\section{Actual Compilation} -\todo{hulp functies voor compileren} +\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} 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 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 fresh labels are reused. +Reusing labels would not give a speed improvement since the labels are removed +in the end. + +\begin{lstlisting}[label={lst:compilation},% + caption={Actual compilation.}] +bclength :: BC -> Int +bclength (BCPush s) = 1 + size (toByteCode s) +bclength ... = ... +bclength x = 1 + consNum{|*|} x + +computeGotos :: [BC] Int -> ([BC], Map Int Int) +computeGotos [] _ = ([], newMap) +computeGotos [BCLab l:xs] i = appSnd ('DM'.put l i) (computeGotos xs i) +computeGotos [x:xs] i = appFst (\bc->[x:bc]) (computeGotos xs (i + bclength x)) + +toRealByteCode :: (ByteCode a b) BCState -> (String, BCState) +toRealByteCode x s +# (s, bc) = runBC x s +# (bc, gtmap) = computeGotos bc 1 += (concat (map (toString o toByteVal) (map (implGotos gtmap) bc)), s) + +toMessages :: MTaskInterval (Main (ByteCode a b)) BCState -> ([MTaskMSGSend], BCState) +toMessages interval x oldstate +# (bc, newstate) = toRealByteCode (unMain x) oldstate +# newsdss = difference newstate.sdss oldstate.sdss += ([MTSds sdsi e\\{sdsi,sdsval=e}<-newsdss] ++ [MTTask interval bc], newstate) +\end{lstlisting} + +\section{Examples} +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. + +\begin{lstlisting}[caption={Thermostat bytecode},language=c] + 1-2 : BCAnalogRead (Analog A0) + 3-6 : BCPush (Int 50) + 7 : BCGre + 8-9 : BCJmpF 17 //Jump to else +10-12: BCPush (Bool 1) +13-14: BCDigitalWrite (Digital D0) +15-16: BCJmp 21 //Jump to end of if +17-19: BCPush (Bool 0) //Else label +20 : BCDigitalWrite (Digital D0) +\end{lstlisting} +\todo{More elaborate example}