Parent Directory | Revision Log

Revision **8** -
(**hide annotations**)
(**download**)
(**as text**)

*Fri Oct 7 03:14:27 2016 UTC*
(6 years, 2 months ago)
by *dashley*

File MIME type: application/x-tex

File size: 43536 byte(s)

File MIME type: application/x-tex

File size: 43536 byte(s)

Commit of Ph.D. topic proposal.

1 | dashley | 8 | %$Header: /home/dashley/cvsrep/e3ft_gpl01/e3ft_gpl01/dtaipubs/cron/2006/phdtopicpropa/phdtopicpropa.tex,v 1.20 2006/03/27 00:10:30 dashley Exp $ |

2 | \documentclass[letterpaper,10pt,titlepage]{article} | ||

3 | % | ||

4 | %\pagestyle{headings} | ||

5 | % | ||

6 | \usepackage{amsmath} | ||

7 | \usepackage{amsfonts} | ||

8 | \usepackage{amssymb} | ||

9 | \usepackage[ansinew]{inputenc} | ||

10 | \usepackage[OT1]{fontenc} | ||

11 | \usepackage{graphicx} | ||

12 | % | ||

13 | \begin{document} | ||

14 | %----------------------------------------------------------------------------------- | ||

15 | \title{Ph.D. Topic Proposal} | ||

16 | \author{\vspace{2cm}\\David T. Ashley\\\texttt{dta@e3ft.com}\\\vspace{2cm}} | ||

17 | \date{\vspace*{8mm}\small{Version Control $ $Revision: 1.20 $ $ \\ | ||

18 | Version Control $ $Date: 2006/03/27 00:10:30 $ $ (UTC) \\ | ||

19 | $ $RCSfile: phdtopicpropa.tex,v $ $ \\ | ||

20 | \LaTeX{} Compilation Date: \today{}}} | ||

21 | \maketitle | ||

22 | |||

23 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

24 | % | ||

25 | \begin{abstract} | ||

26 | This document describes my Ph.D. research interests and provides | ||

27 | supporting information. The interests | ||

28 | (described in \S{}\ref{srin0}) revolve around the mathematical | ||

29 | basis of timed automata systems and code generation | ||

30 | from timed automata models. | ||

31 | \end{abstract} | ||

32 | |||

33 | \clearpage{} | ||

34 | \pagenumbering{roman} %No page number on table of contents. | ||

35 | \tableofcontents{} | ||

36 | \clearpage{} | ||

37 | \listoffigures | ||

38 | \clearpage{} | ||

39 | |||

40 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

41 | %Force the page number to 1. We don't want to number the table of contents | ||

42 | %page. | ||

43 | % | ||

44 | \setcounter{page}{1} | ||

45 | \pagenumbering{arabic} | ||

46 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

47 | |||

48 | \section{The Timed Automata Framework} | ||

49 | \label{staf0} | ||

50 | |||

51 | The framework of timed automata isn't commonplace in electrical | ||

52 | engineering, so this section provides | ||

53 | a description. | ||

54 | |||

55 | |||

56 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

57 | |||

58 | \subsection{The Framework} | ||

59 | \label{staf0:stfw0} | ||

60 | |||

61 | The formal framework of timed automata consists of systems of | ||

62 | automatons, each with discrete states, transitions, and | ||

63 | timers that can be reset to zero on transitions. | ||

64 | |||

65 | The framework includes synchronization mechanisms between automatons (i.e. | ||

66 | automatons may interact in well-defined ways)\@. Synchronization mechanisms | ||

67 | consist of ``soft'' synchronization mechanisms and ``hard'' synchronization | ||

68 | mechanisms. | ||

69 | |||

70 | \begin{itemize} | ||

71 | \item \emph{Soft} synchronization mechanisms involve one automaton having transition | ||

72 | functions that involve the discrete state or timers of another automaton. | ||

73 | \item \emph{Hard} synchronization mechanisms involve events. The semantics | ||

74 | of an event require two or more | ||

75 | automatons to make corresponding transitions at exactly the same time. | ||

76 | \end{itemize} | ||

77 | |||

78 | The details of the framework aren't especially important, | ||

79 | and there are several | ||

80 | variations on the framework\footnote{Variations include | ||

81 | substates, differences in the semantics of events, and dynamics that go beyond | ||

82 | $\dot{t} = 1$ (i.e. hybrid systems).} that don't change the essential properties. | ||

83 | |||

84 | The essential properties of the framework (that don't change with the variations) are: | ||

85 | |||

86 | \begin{itemize} | ||

87 | \item A system of timed automata that interact via synchronization | ||

88 | mechanisms can be mathematically combined into a single | ||

89 | larger automaton with a single | ||

90 | discrete state space. | ||

91 | \item There is some symbolic method of reasoning about what values | ||

92 | timers can attain in each discrete state (polytopes, DBMs, etc.). | ||

93 | \item The symbolic reasoning about timer values often allows reasoning about | ||

94 | properties of the system (reachability, liveness, etc.). | ||

95 | \end{itemize} | ||

96 | |||

97 | Timed automata are recognizeable to any embedded software engineer as | ||

98 | ``state machines''. A typical automotive embedded system consists of many | ||

99 | features and software components involving discrete state. For example, | ||

100 | software to control an automobile drivetrain with features like automatic 4-wheel drive | ||

101 | as well as sensor and actuator failure modes tends to have a very large discrete | ||

102 | space. | ||

103 | |||

104 | As a contrived example of a system of timed automata, consider the problem of | ||

105 | controlling a drawbridge with one motor and two limit switches so that it goes up and down | ||

106 | with period $K_D + K_U$ (Fig. \ref{fig:staf0:stfw0:000}). | ||

107 | |||

108 | \begin{figure} | ||

109 | \centering | ||

110 | \includegraphics[width=4.0in]{system01.eps} | ||

111 | \caption{Example Timed Automata System (Drawbridge Control)} | ||

112 | \label{fig:staf0:stfw0:000} | ||

113 | \end{figure} | ||

114 | |||

115 | Assume that when raising the drawbridge, it is adequate to energize the motor | ||

116 | until the limit switch $U$ closes. However, when closing the drawbridge, | ||

117 | it is necessary to energize the motor for time $K_L$ beyond | ||

118 | when the limit switch $D$ closes (the $B_{DOWNLOCK}$ state in | ||

119 | Fig. \ref{fig:staf0:stfw0:01}). | ||

120 | |||

121 | One way to design such a system is with two automata | ||

122 | (Fig. \ref{fig:staf0:stfw0:00} and Fig. \ref{fig:staf0:stfw0:01}) interacting via | ||

123 | synchronization mechnisms. | ||

124 | |||

125 | The automaton of Fig. \ref{fig:staf0:stfw0:00} alternates between two | ||

126 | states with period $K_D + K_U$. At any point in time, the state of this | ||

127 | automaton indicates whether the drawbridge should be down or up. | ||

128 | |||

129 | \begin{figure} | ||

130 | \centering | ||

131 | \includegraphics[height=2.5in]{exta01.eps} | ||

132 | \caption{Example Timed Automaton (Drawbridge Target Position Determination)} | ||

133 | \label{fig:staf0:stfw0:00} | ||

134 | \end{figure} | ||

135 | |||

136 | The automaton of Fig. \ref{fig:staf0:stfw0:01} directly | ||

137 | determines the energization of the bridge motor as a function of | ||

138 | the limit switches $D$ and $U$, the discrete state of the automaton | ||

139 | of Fig. \ref{fig:staf0:stfw0:00}, and time. | ||

140 | In the $B_{IDLE}$ state, the motor is deenergized. | ||

141 | In the $B_{UP}$ state, the motor is energized to move the | ||

142 | drawbridge up. In the $B_{DOWN}$ and $B_{DOWNLOCK}$ states, | ||

143 | the motor is energized to move the drawbridge down. | ||

144 | |||

145 | \begin{figure} | ||

146 | \centering | ||

147 | \includegraphics[width=4.6in]{exta02.eps} | ||

148 | \caption{Example Timed Automaton (Drawbridge Motor Control)} | ||

149 | \label{fig:staf0:stfw0:01} | ||

150 | \end{figure} | ||

151 | |||

152 | Mathematically, the automata of Figs. | ||

153 | \ref{fig:staf0:stfw0:00} | ||

154 | and | ||

155 | \ref{fig:staf0:stfw0:01} can be combined to give the automaton of | ||

156 | Fig. \ref{fig:staf0:stfw0:02}\@. This mathematical operation is sometimes called the | ||

157 | ``shuffle'' operation. | ||

158 | |||

159 | \begin{figure} | ||

160 | \centering | ||

161 | \includegraphics[width=4.6in]{exta03.eps} | ||

162 | \caption{Example Timed Automaton (Shuffle of Fig. \ref{fig:staf0:stfw0:00} and Fig. \ref{fig:staf0:stfw0:01})} | ||

163 | \label{fig:staf0:stfw0:02} | ||

164 | \end{figure} | ||

165 | |||

166 | In Fig. \ref{fig:staf0:stfw0:02}, each of the eight discrete states | ||

167 | corresponds to one discrete state from Fig. \ref{fig:staf0:stfw0:00} | ||

168 | and one discrete state from In Fig. \ref{fig:staf0:stfw0:01}. | ||

169 | The initial state $A_{D}B_{IDLE}$ corresponds to the initial state | ||

170 | from In Fig. \ref{fig:staf0:stfw0:00} paired with the initial state | ||

171 | from Fig. \ref{fig:staf0:stfw0:01}. | ||

172 | |||

173 | The noteworthy features of Fig. \ref{fig:staf0:stfw0:02} are: | ||

174 | |||

175 | \begin{itemize} | ||

176 | \item It is the result of a mathematical algorithm applied to | ||

177 | Figs. \ref{fig:staf0:stfw0:00} and \ref{fig:staf0:stfw0:01}. | ||

178 | If the underlying system consisted of more than two automata, the | ||

179 | algorithm could be applied repeatedly to generate a single automaton with | ||

180 | a single large discrete state space. | ||

181 | \item The upper bound on the number of discrete states in the shuffle | ||

182 | of two automata is the product of the number of discrete states | ||

183 | in each. Note, however, that $A_{D}B_{UP}$ and $A_{U}B_{DOWN}$ | ||

184 | don't ``truly'' exist. The reason is that the synchronization | ||

185 | mechanisms between the two automata ensure that these states | ||

186 | are instantly exited as soon as they are entered. Thus, a system | ||

187 | of equivalent functionality can be constructed with six discrete | ||

188 | states rather than eight. | ||

189 | \end{itemize} | ||

190 | |||

191 | Although the preceding example is contrived, it illustrates the flavor | ||

192 | of the framework and how separate automata with synchronization mechanisms can be | ||

193 | combined (and perhaps also ``separated'' or ``factored'', \S{}\ref{srin0:star0}). | ||

194 | |||

195 | It should also be apparent that tools can verify a great deal about | ||

196 | the system through symbolic manipulation. Properties that can be verified | ||

197 | include: | ||

198 | |||

199 | \begin{itemize} | ||

200 | \item \emph{Reachability:} it can be symbolically determined whether | ||

201 | or not each state is reachable (the algorithms involve determining | ||

202 | symbolically which values timers can achieve in each discrete state and | ||

203 | comparing that information against transition functions---some transitions | ||

204 | cannot ever be taken). | ||

205 | \item \emph{Liveness:} it can be symbolically determined whether the system | ||

206 | can enter a state where no inputs to the system can cause all of a | ||

207 | set of states to be reachable. | ||

208 | \end{itemize} | ||

209 | |||

210 | The example comes \emph{very} close to the way practical | ||

211 | software systems are constructed. Generally, state machines in | ||

212 | software have transition functions that involve time and the states of | ||

213 | other state machines. | ||

214 | |||

215 | |||

216 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

217 | |||

218 | \subsection{Human Tendencies} | ||

219 | \label{staf0:shtd0} | ||

220 | |||

221 | My experience in industry is that human beings do badly with the | ||

222 | design of stateful controllers. Typical tendencies: | ||

223 | |||

224 | \begin{itemize} | ||

225 | \item \textbf{Bloating of the controller state space:} | ||

226 | \;It is very common for engineers to design a controller with | ||

227 | a discrete state space that is too large. The prototypical | ||

228 | example is an engineer who finds a way to implement a purely combinational | ||

229 | function using sequential logic. | ||

230 | |||

231 | In the most humorous case (purely combinational logic implemented as | ||

232 | sequential logic), | ||

233 | the system usually behaves correctly. Serious software defects | ||

234 | most typically come about through \emph{subtle} design mistakes. A typical software defect | ||

235 | involves two or more software components with some interaction that enter | ||

236 | states such that the software can't recover. | ||

237 | \item \textbf{Inability to comprehend all possible behaviors of the system:} | ||

238 | Very stateful systems tend to be incompatible with human cognitive | ||

239 | ability. Even when the problem is well-defined and when the controller and | ||

240 | plant are operating perfectly, human beings don't do | ||

241 | well at considering every possible behavior. | ||

242 | \item \textbf{Inability to comprehend how the system may behave in the presence | ||

243 | of failures:} | ||

244 | Very stateful systems are often designed to be tolerant of certain types | ||

245 | of sensor and actuator failures (usually in the sense that the failures will | ||

246 | be detected and the system will employ a different algorithm to operate without | ||

247 | a specific sensor or actuator)\@. Such fault detection and tolerance | ||

248 | normally complicates the software design substantially. | ||

249 | |||

250 | However, even without designed-in fault tolerance, there is the need to | ||

251 | design controllers to tolerate the faults that can occur in any practical system. | ||

252 | Specific scenarios that must be tolerated: | ||

253 | |||

254 | \begin{itemize} | ||

255 | \item Spurious reset of the controller (which will normally reset the controller | ||

256 | to its initial state but leave the plant undisturbed). (This directly implies that | ||

257 | the system must recover from the initial state of the controller combined with | ||

258 | any state of the plant.) | ||

259 | \item State upset of the controller (due to electrical noise, internal software errors, | ||

260 | etc.). (This directly implies that the system must recover from any state of | ||

261 | the controller combined with any state of the plant.) | ||

262 | \end{itemize} | ||

263 | |||

264 | Except in simple cases, human beings don't have the cognitive capacity to consider | ||

265 | all possible behaviors when both the controller and the plant may start in any state. | ||

266 | \end{itemize} | ||

267 | |||

268 | One example that comes to mind from product development is an automobile transfer case controller | ||

269 | where it was discovered that if the electrical connector was removed, the transfer case mechanical | ||

270 | components repositioned, and the electrical connection restored; the controller would not | ||

271 | recover into normal operation. Human beings are not good at mentally exploring all possibilities, and even | ||

272 | a disciplined manual process can't be used because the combinations sometimes number in the thousands | ||

273 | or more. A mathematical framework and tool support are required. | ||

274 | |||

275 | |||

276 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

277 | |||

278 | \subsection{Code Generation} | ||

279 | \label{staf0:scgn0} | ||

280 | |||

281 | In most engineering environments, software is generated | ||

282 | from software designs that involve timed automata. (Some of the techniques | ||

283 | used to create compact code are described in \S{}\ref{sfrr0}.) | ||

284 | |||

285 | For some types of systems, there has been success in using | ||

286 | existing tools to generate code directly from the software design | ||

287 | (using tool chains from \emph{The Math Works} or \emph{I-Logix}). It is, | ||

288 | however, known from experience that a clever human programmer can generate | ||

289 | more compact code than any existing tool; so code generation tools have | ||

290 | not penetrated cost-sensitive automotive products involving 32K of FLASH or less. | ||

291 | |||

292 | There are two primary arguments against manual generation of code: | ||

293 | |||

294 | \begin{itemize} | ||

295 | \item Code is redundant with respect to a software design. | ||

296 | In general, it does not make economic sense to maintain redundant | ||

297 | information using human labor. | ||

298 | \item The act of optimizing implementations typically destroys the | ||

299 | clear relationship between design and code. Furthermore, changes | ||

300 | to the design---sometimes even small ones---can invalidate the | ||

301 | mathematical basis for certain optimizations. Optimized code becomes | ||

302 | unmaintainable. It would be more economical to evaluate the viability | ||

303 | of optimizations and to generate code using software tools (rather than | ||

304 | human labor). | ||

305 | \end{itemize} | ||

306 | |||

307 | |||

308 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

309 | |||

310 | \subsection{Formal Verification of Properties} | ||

311 | \label{staf0:svpr0} | ||

312 | |||

313 | Typical design tools provide simulation capability, and there is a large | ||

314 | body of theory and best practice about how to design test cases based on | ||

315 | a stateful design. | ||

316 | |||

317 | Still, the following problems remain: | ||

318 | |||

319 | \begin{itemize} | ||

320 | \item Systems with a large discrete state space elude human | ||

321 | understanding. | ||

322 | \item It is very laborious to test systems with a large discrete | ||

323 | state space. | ||

324 | \item It isn't possible to fully test systems with a large | ||

325 | discrete state space. | ||

326 | \item It is possible (and common) to make a good faith effort at | ||

327 | comprehensively testing systems but still to overlook | ||

328 | unacceptable behavior. | ||

329 | \end{itemize} | ||

330 | |||

331 | \emph{Simulation and testing are not enough.} For complex safety-critical | ||

332 | systems, simulation and testing do not provide enough assurance about the | ||

333 | behavior of the system. | ||

334 | |||

335 | Formal verification of properties would involve making mathematical assertions | ||

336 | about how the system must and must not behave, and then allowing | ||

337 | tools to verify the properties. | ||

338 | |||

339 | Possible types of properties: | ||

340 | |||

341 | \begin{itemize} | ||

342 | \item \emph{Required behavior:} | ||

343 | For example: \emph{When the brake pedal switch is closed, | ||

344 | the brake lights must always come on within 200ms.} | ||

345 | \item \emph{Required absence of behavior:} | ||

346 | For example: \emph{The airbags can never deploy without at least one | ||

347 | body deformation sensor indicating body deformation.} | ||

348 | \item \emph{Liveness:} | ||

349 | For example: \emph{A certain set of states is always reachable by manipulating certain | ||

350 | inputs.} | ||

351 | \end{itemize} | ||

352 | |||

353 | The only tool I'm aware of that allows formal verification of properties | ||

354 | is UPPAAL. However, the modeling framework of | ||

355 | UPPAAL isn't rich enough to support practical embedded systems.\footnote{The | ||

356 | tool chains from \emph{The Math Works} and \emph{I-Logix} don't attempt | ||

357 | formal verification at all.} | ||

358 | |||

359 | I would tend to view formal verification of properties as a last line of defense | ||

360 | against egregious software defects (i.e. as a practice that cannot stand alone)\@. | ||

361 | Formal verification should be combined with all other known | ||

362 | best practices. | ||

363 | |||

364 | |||

365 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

366 | |||

367 | \section{FLASH/ROM Reduction Techniques} | ||

368 | \label{sfrr0} | ||

369 | |||

370 | In this section, I mention some of the FLASH/ROM reduction techniques | ||

371 | used by human programmers. Important points: | ||

372 | |||

373 | \begin{itemize} | ||

374 | \item All of the techniques have a mathematical basis. | ||

375 | \item The techniques are complex to apply and best carried out by tools. | ||

376 | \item The mathematical basis of the techniques is non-trivial. There are | ||

377 | many unexplored corners. | ||

378 | \item The techniques distort the correspondence (i.e. the resemblance) | ||

379 | between design and code, and make code unmaintainable (it would be | ||

380 | better only to generate code from designs and never to maintain | ||

381 | code directly). | ||

382 | \end{itemize} | ||

383 | |||

384 | The list of techniques presented is not exhaustive (far more techniques | ||

385 | exist). | ||

386 | |||

387 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

388 | |||

389 | \subsection{General Paradigm of Software Construction for Small Microcontrollers} | ||

390 | \label{sfrr0:sgsc0} | ||

391 | |||

392 | This discussion is confined entirely to systems where a stateful design is | ||

393 | implemented directly as code (with no tabulation or compression of the design). | ||

394 | Other paradigms are possible. For example, at least one tool on the market implements | ||

395 | stateful designs as state transition tables that are evaluated at runtime by | ||

396 | a table interpreter. My experience with these types of systems is that there | ||

397 | is always a real-time performance penalty (but certainly not always a | ||

398 | FLASH penalty). My research interests do also include event-driven systems | ||

399 | and systems where the design is not implemented directly as code; but these | ||

400 | systems are not mentioned for brevity. | ||

401 | |||

402 | The most common paradigm for small systems is ``\emph{a collection of cooperating | ||

403 | timed automatons}''. The most typical abstraction of these systems is a data-flow | ||

404 | diagram, with RAM variables (i.e. global variables) used as the interfaces. | ||

405 | |||

406 | There is a body of theory and best practice about what separates good software designs | ||

407 | and implementations from bad (Parnas and the classic coupling and cohesion spectrums | ||

408 | come to mind). However, in small systems, it simply isn't possible to | ||

409 | implement the systems using classic ``good'' programming practice---formal parameters, | ||

410 | pointer dereferencing, and access to variables in stack frames all bloat | ||

411 | FLASH size under the weak instruction sets typical of small microcontrollers. | ||

412 | |||

413 | It is helpful to take a step back and consider the possibility that global variables | ||

414 | (the second-strongest form of coupling in the classic coupling spectrum) aren't | ||

415 | inherently harmful; but rather that it is the way in which global variables are | ||

416 | typically used that causes harm. The harmful aspects of global variables | ||

417 | seem to be: | ||

418 | |||

419 | \begin{itemize} | ||

420 | \item If global variables are tested \emph{and assigned} in more than place, | ||

421 | the variable actually becomes an automaton and adds to the | ||

422 | state space of the system. | ||

423 | \item Global variables lead to unrestrained connectivity: \emph{any} | ||

424 | software component can access the variables. Additionally, | ||

425 | state is not ``shed'' as functions return (as happens with formal | ||

426 | parameters and local variables)\@. This leads to connectivity | ||

427 | that often skips levels of the calling tree (making it very | ||

428 | difficult to understand the software). | ||

429 | \end{itemize} | ||

430 | |||

431 | Small systems often have design rules to mitigate the harmful aspects of | ||

432 | global variables. The design rules tend to involve these restrictions: | ||

433 | |||

434 | \begin{itemize} | ||

435 | \item A global variable used as an interface can be assigned by only one | ||

436 | software component (a 1-writer, $n$-reader restriction). | ||

437 | \item A global variable used as an interface has its readers/writers | ||

438 | represented in design documentation (so that the connectivity | ||

439 | created by the global variable isn't accidental or unrestrained). | ||

440 | \end{itemize} | ||

441 | |||

442 | The design rules typically also include provisions for global variables | ||

443 | used as interfaces that are tested and assigned by more than one software | ||

444 | component (i.e. interface automatons). The simplest example of such an | ||

445 | interface is a semaphore that is | ||

446 | set \emph{T} by one software component and tested and set \emph{F} by | ||

447 | another software component, but the design rules are far more general. | ||

448 | |||

449 | Note that tools can be used to allow a system to be phrased in a way | ||

450 | consistent with the traditional coupling spectrum but implemented | ||

451 | efficiently for small microcontrollers. For example, some compilers | ||

452 | are able to analyze the calling tree and place variables of storage | ||

453 | class \emph{automatic} into statically overlaid\footnote{Statically overlaid | ||

454 | based on the calling tree: one function's automatic variables can be overlaid | ||

455 | with another only if an analysis of the calling tree determines that | ||

456 | the two functions cannot be active at the same time.} areas of memory rather than | ||

457 | in a stack frame. Similar tool support could be developed for the notion of | ||

458 | \emph{automatic} bitfields and to restrain the connectivity introduced | ||

459 | by global variables to be consistent with the product design. | ||

460 | |||

461 | |||

462 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

463 | |||

464 | \subsection{Near versus Far (Addressing Modes)} | ||

465 | \label{sfrr0:snvf0} | ||

466 | |||

467 | Most small microcontrollers (TMS370C8, 68HC05, etc.) have two | ||

468 | non-indexed addressing modes, typically called \emph{direct} and | ||

469 | \emph{extended}. Instructions using the direct addressing mode typically | ||

470 | have the address encoded as a single byte, and can address only locations | ||

471 | \$00 through \$FF\@. Instructions using the extended addressing mode | ||

472 | typically have the address encoded as two bytes, and can address | ||

473 | locations \$0000 through \$FFFF. | ||

474 | |||

475 | For lack of better nomenclature, I'll call the RAM locations that can be addressed | ||

476 | using short instructions \emph{near} RAM, and the RAM locations that require | ||

477 | long instructions \emph{far} RAM. | ||

478 | |||

479 | When fixed RAM locations are used as interfaces (\S{}\ref{sfrr0:sgsc0}), | ||

480 | one can save substantial FLASH by allocating the variables that are | ||

481 | referenced most often throughout the software into near RAM. | ||

482 | |||

483 | In automotive software, variables such as gearshift position and vehicle speed | ||

484 | are typically referenced many times throughout FLASH. Most programmers | ||

485 | would automatically place these into near RAM. | ||

486 | |||

487 | However, for most variables, it isn't obvious whether these should be placed | ||

488 | into near or far RAM. | ||

489 | |||

490 | Software developers often write small utility programs to scan all software | ||

491 | modules to determine the number of references to each variable. This information | ||

492 | is then used to allocate the variables with the most references into near RAM. | ||

493 | |||

494 | The FLASH savings from using this technique is typically large. As an example, | ||

495 | assume there are ten variables each referenced 50 times throughout the software. | ||

496 | The savings of placing these variables into near RAM versus far RAM is | ||

497 | typically about $50 \times 10 = 500$ bytes of FLASH (more than 1\% of a | ||

498 | 32K FLASH). | ||

499 | |||

500 | |||

501 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

502 | |||

503 | \subsection{Treatment of Time} | ||

504 | \label{sfrr0:stot0} | ||

505 | |||

506 | The way that time is measured is usually the single most important decision | ||

507 | in a small embedded system. Typically, many software components have to | ||

508 | measure time intervals, so a suboptimal decision about the mechanisms | ||

509 | greatly increases FLASH consumption. | ||

510 | |||

511 | The best mechanism known is to arrange all software timers into | ||

512 | binary decades and to decrement the timers en masse | ||

513 | (Fig. \ref{fig:sfrr0:stot0:00}). | ||

514 | |||

515 | \begin{figure} | ||

516 | \begin{small} | ||

517 | \begin{verbatim} | ||

518 | unsigned char modulo_counter; | ||

519 | unsigned char timers_modulo_1[MOD1_COUNT]; | ||

520 | unsigned char timers_modulo_2[MOD2_COUNT]; | ||

521 | unsigned char timers_modulo_4[MOD4_COUNT]; | ||

522 | |||

523 | void decrement_timers(void) | ||

524 | { | ||

525 | int i; | ||

526 | |||

527 | modulo_counter++; | ||

528 | |||

529 | for (i=0; i<sizeof(timers_modulo_1)/sizeof(timers_modulo_1[0]); i++) | ||

530 | { | ||

531 | if (timers_modulo_1[i]) | ||

532 | timers_modulo_1[i]--; | ||

533 | } | ||

534 | |||

535 | if (modulo_counter & 0x01) | ||

536 | { | ||

537 | for (i=0; i<sizeof(timers_modulo_2)/sizeof(timers_modulo_2[0]); i++) | ||

538 | { | ||

539 | if (timers_modulo_2[i]) | ||

540 | timers_modulo_2[i]--; | ||

541 | } | ||

542 | } | ||

543 | |||

544 | if (modulo_counter & 0x02) | ||

545 | { | ||

546 | for (i=0; i<sizeof(timers_modulo_4)/sizeof(timers_modulo_4[0]); i++) | ||

547 | { | ||

548 | if (timers_modulo_4[i]) | ||

549 | timers_modulo_4[i]--; | ||

550 | } | ||

551 | } | ||

552 | } | ||

553 | \end{verbatim} | ||

554 | \end{small} | ||

555 | \caption{Software Timers Decremented En Masse} | ||

556 | \label{fig:sfrr0:stot0:00} | ||

557 | \end{figure} | ||

558 | |||

559 | When software components must measure time, a byte | ||

560 | (\texttt{timers\_modulo\_4[2]}, for example) is set to a non-zero value. | ||

561 | A separate software component, usually resembling Fig. \ref{fig:sfrr0:stot0:00} but often | ||

562 | implemented in assembly-language, | ||

563 | decrements the byte, but not below zero. | ||

564 | A test against zero will determine if the time period has expired. | ||

565 | |||

566 | The single-byte mechanism combined with binary decades allows any time period | ||

567 | to be measured within 1:128. For example, assume that the binary decades are | ||

568 | $2^q \times 1ms$ (1ms, 2ms, 4ms, etc.) and then that | ||

569 | we wish to measure a time period of 30 minutes. Then | ||

570 | |||

571 | \begin{equation} | ||

572 | 255 (2^q) \geq 1,800,000 | ||

573 | \end{equation} | ||

574 | |||

575 | \begin{equation} | ||

576 | q = \left\lceil \log_2 \frac{1,800,000}{255} \right\rceil = 13 | ||

577 | \end{equation} | ||

578 | |||

579 | A timer resolution of $2^{13} = 8,192$ms with a count of 219 or 220 would in practice be used. | ||

580 | For most automotive applications, measuring 30 minutes within 8 seconds is acceptable. | ||

581 | |||

582 | It is noteworthy that using coarse software timers introduces nondeterminism | ||

583 | into the system (although I've never seen a problem in practice) and probably requires | ||

584 | some adjustment to timed automata algorithms used for verification of properties. | ||

585 | |||

586 | |||

587 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

588 | |||

589 | \subsection{Bitfields of Size One} | ||

590 | \label{sfrr0:sbfi0} | ||

591 | |||

592 | Many small microcontrollers possess extremely efficient instructions | ||

593 | for clearing, setting, and testing individual bits of RAM (especially near | ||

594 | bits). It isn't uncommon for a microcontroller to have an instruction that | ||

595 | will test a bit and conditionally branch. | ||

596 | |||

597 | Note that economies apply only to bitfields of size one. Bitfields of | ||

598 | other sizes require the compiler to mask and shift to obtain the value of the | ||

599 | bitfield, then to shift and mask to store the value back. | ||

600 | |||

601 | The economy of bitfields of size one has several implications for the construction | ||

602 | of embedded software. | ||

603 | |||

604 | \begin{itemize} | ||

605 | \item Variables that are conceptually Boolean should never be | ||

606 | maintained as full bytes. Bitfields are more efficient, both | ||

607 | in FLASH and RAM. | ||

608 | \item In many cases, it is most efficient to maintain discrete state as | ||

609 | bitfields rather than as a byte. A state machine with three | ||

610 | discrete states is often most effectively implemented as two | ||

611 | bitfields with state assignments 0/0, 0/1, and 1/X. | ||

612 | \item It is often most effective to evaluate common Boolean subexpressions and store | ||

613 | the results in bitfields (\S{}\ref{sfrr0:scse0}). | ||

614 | \end{itemize} | ||

615 | |||

616 | |||

617 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

618 | |||

619 | \subsection{Equivalence Classing of Discrete States} | ||

620 | \label{sfrr0:secd0} | ||

621 | |||

622 | The most obvious way to construct a state machine in software is shown in | ||

623 | Fig. \ref{fig:sfrr0:secd0:00}. Discrete state is maintained | ||

624 | as a byte, and each state has a value $\in \{0, \ldots{}, 255\}$. | ||

625 | |||

626 | \begin{figure} | ||

627 | \begin{small} | ||

628 | \begin{verbatim} | ||

629 | switch (state) | ||

630 | { | ||

631 | default: | ||

632 | case 0: | ||

633 | { | ||

634 | if (some_transition_condition) | ||

635 | { | ||

636 | state = 1; | ||

637 | } | ||

638 | break; | ||

639 | } | ||

640 | case 1: | ||

641 | { | ||

642 | if (some_other_transition_condition) | ||

643 | { | ||

644 | state = 0; | ||

645 | } | ||

646 | break; | ||

647 | } | ||

648 | case 2: | ||

649 | { | ||

650 | ... | ||

651 | break; | ||

652 | } | ||

653 | } | ||

654 | \end{verbatim} | ||

655 | \end{small} | ||

656 | \caption{Most Obvious Construction of State Machine in Software} | ||

657 | \label{fig:sfrr0:secd0:00} | ||

658 | \end{figure} | ||

659 | |||

660 | The shortcoming of the approach shown in Fig. \ref{fig:sfrr0:secd0:00} is that | ||

661 | state machines are often accompanied by: | ||

662 | |||

663 | \begin{itemize} | ||

664 | \item Combinational logic that implements combinational functions involving | ||

665 | the discrete state of the state machine being considered. | ||

666 | \item Transition functions in other state machines that depend on the discrete | ||

667 | state of the state machine being considered. | ||

668 | \end{itemize} | ||

669 | |||

670 | |||

671 | \begin{figure} | ||

672 | \begin{small} | ||

673 | \begin{verbatim} | ||

674 | if ( | ||

675 | (state == 0) || (state == 13) || (state == 18) || (state == 30) | ||

676 | || (state == 31) || (state == 51) || (state == 99) | ||

677 | ) | ||

678 | \end{verbatim} | ||

679 | \end{small} | ||

680 | \caption{Typical Test for Membership in a Set of Discrete States} | ||

681 | \label{fig:sfrr0:secd0:01} | ||

682 | \end{figure} | ||

683 | |||

684 | This can often lead to tests of the form shown in | ||

685 | Fig. \ref{fig:sfrr0:secd0:01}. | ||

686 | Such tests are very expensive, both in FLASH consumption and in execution time. | ||

687 | A typical compiler must generate many compare instructions. | ||

688 | |||

689 | One can make the observation that there are many machine instructions that | ||

690 | create equivalence classes within $\mathbb{Z}^+$: | ||

691 | |||

692 | \begin{itemize} | ||

693 | \item An \emph{AND \#1} instruction may create equivalence classes such as | ||

694 | \{0, 2, 4, \ldots{}\} versus \{1, 3, 5, \ldots{}\}. Other \emph{AND} instructions | ||

695 | can create more complex equivalence classes. | ||

696 | \item A \emph{CMP \#n} instruction usually creates three equivalence classes: the integers less than $n$, | ||

697 | $n$, and the integers greater than $n$. | ||

698 | \item There are other machine instructions that create different equivalence classes. | ||

699 | \end{itemize} | ||

700 | |||

701 | The critical question is whether one can assign discrete state values so as to | ||

702 | make the best utilization of the equivalence classes that machine instructions | ||

703 | naturally create. For example, if a test for 10 distinct discrete states occurs | ||

704 | many places in the software, it would make sense to try to assign these | ||

705 | state values so that they are part of an equivalence class that can be | ||

706 | identified immediately by one or two machine instructions. | ||

707 | |||

708 | It should be obvious that if many different tests of discrete state are involved, | ||

709 | identifying an optimal or near-optimal assignment of discrete state values and | ||

710 | the accompanying tests would be very difficult to do by hand. This type of | ||

711 | optimization is best done by software tools. | ||

712 | |||

713 | |||

714 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

715 | |||

716 | \subsection{Ordering of Transition Functions} | ||

717 | \label{sfrr0:sotf0} | ||

718 | |||

719 | It often happens that transition functions have common subexpressions. | ||

720 | For example, consider the code snippet in Fig. \ref{fig:sfrr0:sotf0:00}. | ||

721 | The subexpression ``\texttt{A \&\& B}'' is common to both transitions | ||

722 | out of State 0. | ||

723 | |||

724 | \begin{figure} | ||

725 | \begin{small} | ||

726 | \begin{verbatim} | ||

727 | switch (state) | ||

728 | { | ||

729 | default: | ||

730 | case 0: | ||

731 | { | ||

732 | if (A && B && C) | ||

733 | { | ||

734 | state = 1; | ||

735 | } | ||

736 | else if (A && B && !D) | ||

737 | { | ||

738 | state = 2; | ||

739 | } | ||

740 | break; | ||

741 | } | ||

742 | case 1: | ||

743 | { | ||

744 | ... | ||

745 | break; | ||

746 | } | ||

747 | case 2: | ||

748 | { | ||

749 | ... | ||

750 | break; | ||

751 | } | ||

752 | } | ||

753 | \end{verbatim} | ||

754 | \end{small} | ||

755 | \caption{State Machine Before Control Flow Removal of Common Subexpression} | ||

756 | \label{fig:sfrr0:sotf0:00} | ||

757 | \end{figure} | ||

758 | |||

759 | The code can be optimized to evaluate this subexpression only once | ||

760 | (Fig. \ref{fig:sfrr0:sotf0:01}). | ||

761 | |||

762 | \begin{figure} | ||

763 | \begin{small} | ||

764 | \begin{verbatim} | ||

765 | switch (state) | ||

766 | { | ||

767 | default: | ||

768 | case 0: | ||

769 | { | ||

770 | if (A && B) | ||

771 | { | ||

772 | if (C) | ||

773 | { | ||

774 | state = 1; | ||

775 | } | ||

776 | else if (!D) | ||

777 | { | ||

778 | state = 2; | ||

779 | } | ||

780 | } | ||

781 | break; | ||

782 | } | ||

783 | case 1: | ||

784 | { | ||

785 | ... | ||

786 | break; | ||

787 | } | ||

788 | case 2: | ||

789 | { | ||

790 | ... | ||

791 | break; | ||

792 | } | ||

793 | } | ||

794 | \end{verbatim} | ||

795 | \end{small} | ||

796 | \caption{State Machine After Control Flow Removal of Common Subexpression} | ||

797 | \label{fig:sfrr0:sotf0:01} | ||

798 | \end{figure} | ||

799 | |||

800 | In the trivial case presented, it is easy to identify the subexpression | ||

801 | and rearrange the code so that it is evaluated only once. However, more complex cases | ||

802 | involve logical implication; i.e. there is not an identifiable subexpression, but there | ||

803 | is still a way to rearrange the code for better efficiency. Such analysis is | ||

804 | best done by software tools. | ||

805 | |||

806 | |||

807 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

808 | |||

809 | \subsection{Common Subexpression Elimination} | ||

810 | \label{sfrr0:scse0} | ||

811 | |||

812 | It often occurs that the same subexpression appears in transition functions from | ||

813 | more than one discrete state. It can be economical to rearrange the | ||

814 | code to evaluate such subexpressions | ||

815 | only once. Two approaches occur in practice: | ||

816 | |||

817 | \begin{itemize} | ||

818 | \item The subexpression is evaluated once, regardless of discrete state, and the | ||

819 | result is placed in a temporary variable (often a bitfield if the expression | ||

820 | has a Boolean result). | ||

821 | \item The evaluation of the subexpression is implemented as a subroutine, and | ||

822 | the subroutine is called from more than one transition function. | ||

823 | \end{itemize} | ||

824 | |||

825 | Each of these two approaches has advantages and disadvantages. | ||

826 | |||

827 | Identifying common subexpressions and deciding how to eliminate the FLASH | ||

828 | penalty associated with duplicated code is a tedious task and best done | ||

829 | by software tools. | ||

830 | |||

831 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

832 | |||

833 | \subsection{Farey Series Approximations} | ||

834 | \label{sfrr0:sfsa0} | ||

835 | |||

836 | Many modern microcontrollers have an efficient integer multiplication | ||

837 | instruction, and some also have an efficient integer division instruction. | ||

838 | Fixed-point arithmetic is the norm in small microcontroller work, and it | ||

839 | is common to want to approximate functions of the form | ||

840 | |||

841 | \begin{equation} | ||

842 | y = r_I x | ||

843 | \end{equation} | ||

844 | |||

845 | \noindent{}with $r_I \in \mathbb{R}^+$ and $x,y \in \mathbb{Z}^+$. $r_I$ is the | ||

846 | ``ideal'' scaling factor, which may be irrational. | ||

847 | |||

848 | If the processor has an integer multiplication instruction but no division | ||

849 | instruction, it is usually most effective to choose | ||

850 | |||

851 | \begin{equation} | ||

852 | r_A = \frac{h}{2^q} \approx r_I, | ||

853 | \end{equation} | ||

854 | |||

855 | \noindent{}with the division by a power of two implemented via a right shift. | ||

856 | |||

857 | However, if the processor also has an integer division instruction, we may choose | ||

858 | |||

859 | \begin{equation} | ||

860 | r_A = \frac{h}{k} \approx r_I, | ||

861 | \end{equation} | ||

862 | |||

863 | \noindent{}with $k$ not required to be a power of two. The specific function | ||

864 | implemented is usually | ||

865 | |||

866 | \begin{equation} | ||

867 | y = \left\lfloor \frac{hx}{k} \right\rfloor , | ||

868 | \end{equation} | ||

869 | |||

870 | \noindent{}or perhaps | ||

871 | |||

872 | \begin{equation} | ||

873 | y = \left\lfloor \frac{hx + z}{k} \right\rfloor , | ||

874 | \end{equation} | ||

875 | |||

876 | \noindent{}where $z \in \mathbb{Z}$ is used to shift the result so as to | ||

877 | provide a tighter bound on the error introduced due to truncation of the | ||

878 | division. | ||

879 | |||

880 | $h$ and $k$ are constrained by the sizes of operands accepted by the | ||

881 | machine instructions ($h \leq h_{MAX}$ and $k \leq k_{MAX}$). | ||

882 | There is an algorithm from number theory (involving Farey series and | ||

883 | continued fractions) that will allow the selection of $h$ and $k$ subject | ||

884 | to the constraints. The algorithm is $O(\log N)$ and so can be applied | ||

885 | to find best rational approximations even for processors that accommodate | ||

886 | 32- or 64-bit operands.\footnote{The computational complexity of the algorithm is | ||

887 | a significant point, as $2^{64}$ (or $2^{128}$) is a very large number.} | ||

888 | |||

889 | For example, the best rational approximation to $\pi$ with | ||

890 | numerator and denominator not exceeding $2^{16}-1$ is 65,298/20,785\@. | ||

891 | On a processor with a 16-bit $\times$ 16-bit multiplication instruction and a | ||

892 | 32-bit / 16-bit division instruction, one can approximate | ||

893 | |||

894 | \begin{equation} | ||

895 | y = \pi x | ||

896 | \end{equation} | ||

897 | |||

898 | \noindent{}with | ||

899 | |||

900 | \begin{equation} | ||

901 | y = \left\lfloor \frac{65,\!298 x}{20,\!785} \right\rfloor | ||

902 | \end{equation} | ||

903 | |||

904 | \noindent{}very efficiently (typically 2-4 machine instructions). | ||

905 | |||

906 | |||

907 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

908 | |||

909 | \subsection{Vertical Counters} | ||

910 | \label{sfrr0:svcn0} | ||

911 | |||

912 | The traditional arrangement for sequential logic is a | ||

913 | \texttt{switch()} statement (this might also be called | ||

914 | a ``horizontal'' counter). However, in some applications that must | ||

915 | implement many identical sequential mappings, it is | ||

916 | efficient to arrange the state vector so that the state of each sequential | ||

917 | mapping consists of a bit in the same position from several bytes. This | ||

918 | is called a ``vertical'' counter.\footnote{It is suspected that the nomenclature | ||

919 | \emph{vertical counter} comes about because if one arranges the 0s and 1s of | ||

920 | bytes horizontally, the state of an individual sequential machine consists | ||

921 | of a vertical row of bits.} | ||

922 | |||

923 | An example of a vertical counter application is 3/3 debouncing---a filtering | ||

924 | function where a discrete input must be in the same state for 3 consecutive | ||

925 | instants of discrete time before the output may change to that state. | ||

926 | |||

927 | If $A$ is the most recent sample, $B$ is the next-most-recent sample, | ||

928 | $C$ is the oldest sample, and $O$ is the output (assumed maintained | ||

929 | as a RAM location) Fig. \ref{fig:sfrr0:svcn0:00} | ||

930 | supplies the Karnaugh map for 3/3 | ||

931 | debouncing. | ||

932 | |||

933 | \begin{figure} | ||

934 | \centering | ||

935 | \includegraphics[height=2.0in]{kmap33db.eps} | ||

936 | \caption{Karnaugh Map Of 3/3 Debouncing} | ||

937 | \label{fig:sfrr0:svcn0:00} | ||

938 | \end{figure} | ||

939 | |||

940 | It can be seen from the figure that the expression for the output is | ||

941 | |||

942 | \begin{equation} | ||

943 | \label{eq:sfrr0:svcn0:01} | ||

944 | ABC + AO + BO + CO = ABC + O(A + B + C). | ||

945 | \end{equation} | ||

946 | |||

947 | Intuitively, (\ref{eq:sfrr0:svcn0:01}) makes sense---the output | ||

948 | will be unconditionally \emph{T} if all three of the most recent samples | ||

949 | are \emph{T} | ||

950 | ($ABC$). The output will also be \emph{T} if the previous output was \emph{T} | ||

951 | and at least one of the most recent samples are \emph{T} [$O(A+B+C)$]---at least | ||

952 | one \emph{T} recent sample blocks the output from transition to \emph{F}. | ||

953 | |||

954 | Figure \ref{fig:sfrr0:svcn0:01} supplies the C-language | ||

955 | code to implement 3/3 debouncing as a vertical mapping. | ||

956 | A C-compiler will typically implement this code very directly | ||

957 | using the bitwise logical instructions of the machine. | ||

958 | |||

959 | \begin{figure} | ||

960 | \begin{verbatim} | ||

961 | /**************************************************************/ | ||

962 | /* Assume: */ | ||

963 | /* A : Most recent sample (i.e. at t(0)), arranged as */ | ||

964 | /* a group of 8 bits. */ | ||

965 | /* B : Next most recent sample t(-1). */ | ||

966 | /* C : Oldest sample t(-2). */ | ||

967 | /* output : Debounced collection of 8 bits presented to */ | ||

968 | /* software internals. Note that this is both */ | ||

969 | /* an input (to the combinational mapping) and */ | ||

970 | /* the new result. */ | ||

971 | /**************************************************************/ | ||

972 | |||

973 | output = (A & B & C) | (output & (A | B | C)); | ||

974 | |||

975 | /* End of code. */ | ||

976 | \end{verbatim} | ||

977 | \caption{C-Language Implementation Of 3/3 Debouncing} | ||

978 | \label{fig:sfrr0:svcn0:01} | ||

979 | \end{figure} | ||

980 | |||

981 | |||

982 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

983 | |||

984 | \section{Research Interests} | ||

985 | \label{srin0} | ||

986 | |||

987 | This section enumerates my specific research interests. | ||

988 | |||

989 | |||

990 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

991 | |||

992 | \subsection{Mathematical Properties of Timed Automata Systems} | ||

993 | \label{srin0:star0} | ||

994 | |||

995 | I have interest in the mathematical properties of timed automata systems, | ||

996 | including these questions: | ||

997 | |||

998 | \begin{itemize} | ||

999 | \item Can these systems be rearranged (independent of code generation) for more | ||

1000 | efficient implementation? Is there some canonical form? | ||

1001 | \item Can an automaton be ``factored'' into components (i.e. the reverse | ||

1002 | operation of ``shuffle'' illustrated in Figs. | ||

1003 | \ref{fig:staf0:stfw0:00}, \ref{fig:staf0:stfw0:01}, and \ref{fig:staf0:stfw0:02})? | ||

1004 | \item Is the factorization unique\footnote{In the same sense that the | ||

1005 | fundamental theorem of arithmetic guarantees that a composite | ||

1006 | can have only one unique factorization into primes.} | ||

1007 | or can it be made unique according | ||

1008 | to some metric? | ||

1009 | \item Can algorithms spot suboptimal designs and coach | ||

1010 | human programmers?\footnote{Example of a suboptimal design: | ||

1011 | identical behavior could be achieved using a simpler design.} | ||

1012 | \end{itemize} | ||

1013 | |||

1014 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

1015 | |||

1016 | \subsection{Code Generation from Systems of Timed Automata} | ||

1017 | \label{srin0:snvf0} | ||

1018 | |||

1019 | I have interest in the mathematics of code generation from systems of timed | ||

1020 | automata. One might make the observation that all of the techniques | ||

1021 | described in \S{}\ref{sfrr0} are individual and seemingly disjoint techniques that | ||

1022 | come about through human ingenuity. I am interested in: | ||

1023 | |||

1024 | \begin{itemize} | ||

1025 | \item Any unified mathematical framework that includes all of the techniques. | ||

1026 | For example, can one find a common framework or way of thinking that includes both | ||

1027 | Farey series approximations and vertical counters? | ||

1028 | \item Any mathematical framework that, given a smorgasbord of disjoint techniques, | ||

1029 | can predict how to apply them to obtain optimal results (this is also | ||

1030 | a function of the processor instruction set). (Cost matrices and | ||

1031 | least-squares methods come to mind immediately, but I'd like to examine | ||

1032 | this more closely.) | ||

1033 | \end{itemize} | ||

1034 | |||

1035 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

1036 | |||

1037 | \subsection{Code Generation and Formal Verification of Properties in the Same Framework} | ||

1038 | \label{srin0:sgvs0} | ||

1039 | |||

1040 | There seem to be no existing tools that will allow code generation (from | ||

1041 | a timed automata model) and the | ||

1042 | verification of formal properties in the same framework. In addition, the tools | ||

1043 | that do generate code (for small systems) can't optimize as effectively as a | ||

1044 | human programmer. With a more sound mathematical basis for optimization, | ||

1045 | I believe that tools should be able to optimize more effectively | ||

1046 | than a human programmer. | ||

1047 | |||

1048 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

1049 | |||

1050 | \subsection{Enterprise Content Management} | ||

1051 | \label{srin0:secm0} | ||

1052 | |||

1053 | I administer web-based version control and defect-tracking databases. This type of | ||

1054 | technology is critical because human beings don't deal well with complexity and | ||

1055 | there is the inherent need to serialize (one bug at a time, one change at a time, etc.). | ||

1056 | |||

1057 | I have some interest in enterprise content management | ||

1058 | (see, for example, \emph{Alfresco}), especially the | ||

1059 | buy-versus-build dilemma and the difficulty | ||

1060 | and cost of developing custom in-house tools that are tailored to an individual | ||

1061 | company's processes (I have some ideas in this area). | ||

1062 | |||

1063 | |||

1064 | %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% | ||

1065 | \end{document} | ||

1066 | % | ||

1067 | %$Log: phdtopicpropa.tex,v $ | ||

1068 | %Revision 1.20 2006/03/27 00:10:30 dashley | ||

1069 | %Presumed final edits. | ||

1070 | % | ||

1071 | %Revision 1.19 2006/03/26 23:26:23 dashley | ||

1072 | %Edits. | ||

1073 | % | ||

1074 | %Revision 1.18 2006/03/26 02:22:21 dashley | ||

1075 | %Edits. | ||

1076 | % | ||

1077 | %End of $RCSfile: phdtopicpropa.tex,v $. | ||

1078 |

dashley@gmail.com | ViewVC Help |

Powered by ViewVC 1.1.25 |