X-Git-Url: https://git.martlubbers.net/?a=blobdiff_plain;f=results.mtask.tex;h=20a51f1702c6d9ab8d065109e74517d343d0ab3a;hb=b8e0188d0d4b4f321259e036807b439c85753828;hp=377a8cb6e98f5931c6088777fc958968fa399164;hpb=6a613ef68371fc249a0987b3c5376547e2f386ba;p=msc-thesis1617.git diff --git a/results.mtask.tex b/results.mtask.tex index 377a8cb..20a51f1 100644 --- a/results.mtask.tex +++ b/results.mtask.tex @@ -1,39 +1,92 @@ -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. +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 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} +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. -\section{Bytecode compilation} +\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 as a parameter the number of milliseconds to wait + in between executions. \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. 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. +\end{itemize} + +\subsection{\glspl{SDS}} +\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 \gls{SDS} +is updated, a broadcast to everyone in the system watching is made to notify +them of the update. \glspl{SDS} can update very 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. + +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. The existing views can choose to implement it 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}\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 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. +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}) 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} 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 ()) @@ -43,8 +96,8 @@ accordingly. , sdsval :: BCValue } :: BCState = - { freshl :: [Int] - , freshs :: [Int] + { freshl :: Int + , freshs :: Int , sdss :: [BCShare] } @@ -63,15 +116,14 @@ instance serial ByteCode \section{Implementation} \subsection{Instruction Set} 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 the highest expressively while keeping all +instruction 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}] @@ -99,17 +151,16 @@ 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 can be 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 +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 +this, several 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 @@ -119,7 +170,7 @@ to the \emph{Writer} value. 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) @@ -132,8 +183,8 @@ unBC (BC x) = x \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. +\CI{boolExpr} 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}] @@ -148,41 +199,70 @@ 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 \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 and then 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}}] +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} \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. +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 share to -the actual state with the value obtained from the function. The exact +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 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 +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 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 -Listing~\ref{lst:assignmentview}. +one \CI{BCSdsFetch} instruction with the correct \gls{SDS} embedded. Assigning +to an analog pin will result in the \gls{RWST} containing the \CI{BCAnalogRead} +instruction. When the assignable is not a read from but assigned to, the +instruction will be rewritten as a store instruction. Resulting in an +\CI{BCSdsStore} or \CI{BCAnalogWrite} instruction respectively. The +implementation for this is given in Listing~\ref{lst:assignmentview}. \begin{lstlisting}[label={lst:assignmentview},% caption={Bytecode view implementation for assignment.}] @@ -195,4 +275,103 @@ makeStore [...] = [...] \end{lstlisting} \section{Actual Compilation} -\todo{hulp functies voor compileren} +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. +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 +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. +Reusing labels would not give a speed improvement since the labels are removed +anyway 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{Example} +The heating 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} + +\section{Interpreter} +The client contains an interpreter to execute a \gls{Task}'s bytecode. + +Before execution some preparatory work is done. The stack will be initialized +and the program counter and stack pointer are set to zero and the bottom +respectively. Then, the interpreter executes one step at the time while the +program counter is smaller than the program length. The code for this is listed +in Listing~\ref{lst:interpr}. One execution step is basically a big switch +statement going over all possible bytecode instructions. Some instructions are +detailed upon in the listing. The \CI{BCPush} instruction is a little more +complicated in real life because some decoding will take place as not all +\CI{BCValue}'s are of the same length. + +\begin{lstlisting}[language=C,label={lst:interpr},% + caption={Rough code outline for interpretation}] +#define f16(p) program[pc]*265+program[pc+1] + +void run_task(struct task *t){ + uint8_t *program = t->bc; + int plen = t->tasklength; + int pc = 0; + int sp = 0; + while(pc < plen){ + switch(program[pc++]){ + case BCNOP: + break; + case BCPUSH: + stack[sp++] = pc++ //Simplified + break; + case BCPOP: + sp--; + break; + case BCSDSSTORE: + sds_store(f16(pc), stack[--sp]); + pc+=2; + break; + // ... + case BCADD: trace("add"); + stack[sp-2] = stack[sp-2] + stack[sp-1]; + sp -= 1; + break; + // ... + case BCJMPT: trace("jmpt to %d", program[pc]); + pc = stack[--sp] ? program[pc]-1 : pc+1; + break; +} +\end{lstlisting}