X-Git-Url: https://git.martlubbers.net/?a=blobdiff_plain;f=results.mtask.tex;h=a939d4f4b2f4447295eed77854d34e35c8803d21;hb=ea7fe3a71df1e5a5da335057b956fe69c4718249;hp=83cc7094edb2d7321ce1c871bb8ea864129ff334;hpb=66de2590bcb4046b92ea54bcd3e55b38208be17b;p=msc-thesis1617.git diff --git a/results.mtask.tex b/results.mtask.tex index 83cc709..a939d4f 100644 --- a/results.mtask.tex +++ b/results.mtask.tex @@ -1,20 +1,20 @@ 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 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} +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{\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 runs some \glspl{Task}. \glspl{Task} in the new system are -\CI{Main} objects with a program inside that does not contain \glspl{Task} but -are a \gls{Task} as a whole. 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}. +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} @@ -38,16 +38,17 @@ strategies as reflected in the \CI{MTTask}. press of a button. \end{itemize} -\subsection{\glspl{SDS}} -\Glspl{SDS} on a client are available on the server as well. 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 bit differently on an \gls{mTask} device than in 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 an update. -\glspl{SDS} on the device can update very often and the update might not be the -final value it will get. Therefore a device must publish the \gls{SDS} -explicitly to save bandwidth. +\section{\gls{SDS} semantics} +\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} @@ -59,7 +60,7 @@ class sdspub v where pub :: (v t Upd) -> v t Expr | type t \end{lstlisting} -\section{Bytecode compilation}\label{sec:compiler} +\section{Bytecode compilation view}\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 encapsulated in the type \CI{ByteCode}. As @@ -71,20 +72,21 @@ 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 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. +\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 ()) @@ -111,18 +113,16 @@ instance arith ByteCode instance serial ByteCode \end{lstlisting} -\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 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}] @@ -150,11 +150,10 @@ instructions. | BCReturn \end{lstlisting} -All instructions 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 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 @@ -183,8 +182,8 @@ 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}] @@ -199,13 +198,14 @@ instance userLed ByteCode where \end{lstlisting} \subsection{Control Flow} -Sequence 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. +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}}] @@ -232,8 +232,8 @@ instance noOp ByteCode where Shared data sources must be acquired from 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 +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},% @@ -242,7 +242,7 @@ freshshare = get >>= \st=:{freshs}->put {st & freshs=freshs+1} >>| pure freshs instance sds ByteCode where sds f = {main = BC (freshshare - >>= \sdsi->pure {BCShare | sdsi=sdsi,sdsval=BCValue 0} + >>= \sdsi->pure {BCShare|sdsi=sdsi,sdsval=BCValue 0} >>= \sds->pure (f (tell` [BCSdsFetch sds])) >>= \(v In bdy)->modify (addSDS sds v) >>| unBC (unMain bdy)) @@ -253,13 +253,15 @@ instance sdspub ByteCode where addSDS sds v s = {s & sdss=[{sds & sdsval=BCValue v}:s.sdss]} \end{lstlisting} -All assignable types compile to a \gls{RWST} that writes one instruction. For -example, using a \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.}] @@ -271,16 +273,17 @@ makeStore [BCDigitalRead i] = [BCDigitalWrite i] makeStore [...] = [...] \end{lstlisting} -\section{Actual Compilation} +\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} in a message. -The \glspl{SDS} that were not already sent to the device are also placed in +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 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. +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.}] @@ -307,7 +310,7 @@ toMessages interval x oldstate = ([MTSds sdsi e\\{sdsi,sdsval=e}<-newsdss] ++ [MTTask interval bc], newstate) \end{lstlisting} -\section{Example} +\section{Examples} 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. @@ -323,51 +326,5 @@ position in the program memory. 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. - -First 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} +\todo{More elaborate example} +\todo{Add return instruction}