An Embedded Software Primer - David E. Simon

CONTENS

7

More Operting System Services 7.1 7.2 .3 7.4 7

8

82 83 84 8. 8.6 7

Overvew 21 Principles 217 An Exampe 233 Encapsuating Semaphore and Queues 244 Har Rea-me Scheduling Consideraions Saving Memory Space 24 Saving Power 27 Capter Summary 29 Probems 260 ·

23

Embedded Software evelopment os 91 9.2 9.3

10

99

Basic Design Using a Real-Time Operating System 215 8.

9

Message Queues, Mailboxes and Pipes 73 Timer Functions 184 Events 191 Memory Management 195 Interrupt Routnes in an ROS Environment Chapter ummary 206 Problems 207

173

Host and Target Machnes 261 Lnker/Locators fr Embedded Sofware 263 Getting Embeded Sofware nto the Target System Chapter Summar 280

ebuggng Techiques 101 12 10.3

Testng on Your Hos Machine nsruction Set Simators 302 The assert Macro 304

283 28

261

276

lX

X

C:oNIFTS

14

Using Laboatory Tools

Chapte Sumary Pobles 32

11

26

An Example System 11. 1  

307

329

Wa  Progra Dos 30 Envionmnt n c  Pogr Os A Gud o h Soc Co 33 Souc o 9 Sumary 42 Problems

Afo

405

F Rg Ix

49

4

407

333

Preface

This book is to hep you learn the basic principes of writing sofware  embedded systems. I surveys the issues and discusses the various techniques  dng wh the n paticular, it dscuse approaches to the aproprite use of the ea-tme operatng systes upon whch uch ebedded sowae s ased.  addton to expaning what these systes do this book points out how you can use the ost eectivey You need kow nothing about ebedded-systes sowre and is probles to read ths book; book; we'l dscss everything everythi ng o the very beginning. Yo shoud e a wth basc compute prograng concepts: you ght be a soware engineer wth a year or ore of experience or perhaps a student  with a few prograing courses under your et You should understand he polms nvoved n witing appicaon pogas This book requirs a reading knowedge of the  prograng language snc C s the ingua anc of ebeded systems you w have to ean t sooner o later i you hope to get into te ed A itte knowedge of asseby anguage wil also be hep. You have no doubt seen any books aout soware that are 80 or 9 or eve 1 page og Presualy you have notced by now that this book i much sae than that This s intentonathe dea s that you igh actuay  want to read al a l the way through it. This ook is not entited Everything Ter Is to Know about Embedded Syst Softwae. Noody could write that ook and if oeone coud and dd you woudnt want to red it anyway This ook is oe ke Wat Yo Need to Know to Get Started n mbedded Stem Sotwar, teng you enough that youl unstand he ssues you wi ce and gettng you started on ndig the inration bout your partcua syste so hat you can eove those issues Ths book is not specc to any microprocesso or eal-ie operating syste o s t oiented towads any patcua softwr design methodoogy The principles are the sae regardess of which mcroprocesso and whch e tie operang syste and which soware design ethdoogy you use We  wil concentrate on te principlesprincipes principlespr incipes that you can appy to amost

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PRFAC

any embedded syste projec. When you need o know he pec f yur iropresor n you eal- prng syse, o  t  manuas ha hardwe and sofware vendors povide wih he pc p c This book wi hep you know wha inraion o ook r This book is no academc or heoreica; i oers enineerin inrmaion and enineerin advice In shor his book is he cornersone o he knowee ha you' nee r  wriin  wrii n ebedesys ebe desysems ems soware Davd E. Smon

Ackowledgments

No one hs enough god ides   boo sch s ths o the peseveac to see it thoug wthout hep om othe peope. So he-moe o les i honoogi odes the story of his bo nd the peope who hepe e tun it into et Fist, thns e due to the eope t Pobts Copotion: to A. J Nicho who hs mde the compn the thought highquli sow envioent tht t s; to Miche Gisch  the ongong dbtes on ebeddedss design nd oding se; to Richd Steinbeg who checed the code exe in this book nd to Ric Vibg who evewed the two hptes on hdwe nd oeted  nume of m misonceptions M wife Lnn Godn encouged e to wite this boo pediting oet s it tuned outtht I woud enjo dong it Thn ou  gett me stted nd thns  the editng hep  ven if ou e ws ight ot the ne points of Engish usge Thn ou to  hfdozen csses  of students to those of ou who ed the dvned uestions nd ed e to i  thning to those o o who sed te eement question nd ed e to i m xpnton nd to  of ou who sueed in sence wth e vesions of the mnusp hns to the smt peope t Dgon Sstems Inc who wote Nat1rlySpeking  voice eognition pog good enough to ow me to pe  mnusipt whie inuie pevented me om tpng much A huge thns to Jen bosse  giing pemission to incude his ete opeting sstem µC!OS, s pt of ths boo You hve done the wod   vo in wting this sstem nd n owing it to be used ee  educton puposes A thn ou to John Keenn wh tught me  ot of wht I ow bot hdwe nd who stightened out  few undes tht mde it into the mnusipt The owing peope eviewed the st vesion of the mnusipt n povided ems of good suggestions mn of which  incopoted no t

XV

iC K NOWLEDGMTS

book: Anono Bigaz, Fred Clegg Davd Cua Mch Eag Joh Kwan Tom Lyon Lyon and Steve Vnok. hank o a ank are de o Mke Hume a Zog who gv ps to u e hema exale a he end of Caer 3 and wh rn down  legble oy of  Fnay hank o Debbe aery and aqueyn Douee ho heherded h book hrough  varou age; o nn ngh and Regna no wo oned o a o oe hng ha ad omeow made ene wen I  we hem bu ddn' aer when omeone ee red  read em and o aue Mue o urned my u kee no egbe gue

About Ts Book and the Accompanyng CD-ROM

The Perversities of Embedded Sysem O vy uua apc of mbddd yms i ha · rminolo uoudg m i o y cosse Fo y cocp, h a wo o h d wod. o y wod  a u o  suly d maig You w ju ha o l wh hs polm I his book w l o ou h aao  mag;  w wi asig a spcc maig  ach wod so a w do' g co1sd Wh you a adig oh ooks o akig o po, how youll ha o b awa th hi wod may ma somg ligy di om wha y ma i h ook Aoh uua olm is ha h m mddd syt co such a oad ag of oduc ha galizaio a difcul Sym a buil  wih micopocssos a di a h Z8 a 8-bi micooco ha ao  u xal mmoy o h PowPC, a 32-bi micopocso ha c acc gigabs Th cod iz o h appicaio ais om ud 500 bys o mios o y Bcau of hi ad bcau of  w aiy of applaos mbddd sowa  a ld  whic o wdm is uisal Ay u lowd by 85 c of g a pa of  accpd go of s pcc a o b ok by  o 15 c ju o g  ym o wok s ook  w cu o  u)s of  85 c mhazg  cc ad  asog d   us ad hg you dcd w you soud ow h como acc o f you oc  pa of h 5 c

Cha per De penence n Ts Book oug  ook  dd  be ad ag houg d aoug y ca dds a as a l o  cas a pcd  ; you ca k oud f you k Sc hs bo s y suc a  y giig you ay b abl o k om c i ou aady kow som of h ia

XV

ABOUT THS BOOK

The mos imporan deendencie among te chae e ow  e aa hee. 1. A First Look a Embedded Sysems

 Hadware

 Ierus

undamens r he Software Engieer

 Adcd Hardwae ndametas

9 Deveopmen Tools

 In duc i  o Real-me Oe  a ain g stm

0 Debgg g echques

5 Sur  are Acitecte

7 Me e Opratng Sysem vces

8 B Dig Ug a Rl .pei Syem

  xp  Sye

I you aleay ko abo haae,  exae o f yo o oe' eque a you ko anyh a  yo ca k Cae 2 a 3 Hove don y o ead Cae 6  ou ea Cae 4 o ko aou he maeia n  C++

Aough C++  a ceany oua laa  e eee-e  od you   ee   h ook T   i  t  e  to s o rae o om ung C hc  oua  th embd-sy   e ae goo eao i  ola  e aplictio w. Hver, oe o· e acknolee iavaae o C +   h    pi ae  any ay uc moe cul a u hn C T p rgrmi e ce   oo ay ua  C n  C+ (n  A J A,

ABouT Tms ooK I

xvn

.

and any other l�ngage in whic o miht hoose to progra yor embedded system, r that matter). herere r the prposes of istration n this book it maes sense o se ear of the ompiatios of  + +

C!!

One of the probems of providing nderstandabe exampes in a book sh as this (and in t one of he probems of software in genera) is hat imporan poins end to ge os in a moass of detail. o prevent that om happening soe of the· exampes in ths book i o be written entirey in  Instead hey wi be written in   is idenia to , exept tht wherever yo pt wo exlamation points he omper does waeve is esibed aer those examation points Fo exmpe: if X  0) {  Read time value fom the harwae !! Do a 11 the necesay ugy arhmetc y =  esut of the ugy athmetc  (y > 97   Tun on the warnn ht

f x is no zero then his program does whateer is neessary to read he ae om the hadwre ime hen it does vaios neessary aations and sores the rest in y. f y is geae than  this program trns on the warning ight   Rest assed that we only se he speia atre of  r sh things as hardware-dependent ode or sei alations needed r some arane appiaion. he pars of he examples that pertain  the point being made are witen in pain od ania  1

. It would be nice if we ou a re a  u pbms in  u ununaey, he coi r C is  une eveen.

XVlll ABOU THIS OOK

H Vl Nm Many of th code exampls in tis book us  convntion r nming varibls cl  ere is  brif introuction to tt onvntion. In ungr ian, th nam of a vribl ontins inrmtion bout its typ For ml nams r int  vribs bgn wt th lttr "i "i '' nms r byt (unsiged char)  vriabls bgin with by n so on on  n iton rtin pr prss on vrib nams indicat tt  vriabl is  pointr (p_) n rr (a), n so on r ar som som typicl typ icl vrib nms an wat you cn infr bout th variabls variabls om thir nms: byEror- bt vrbl (tt contins n ror co probbl) H-an integr (that ontins th numbr of  tnk prps) p_  T- ponter to a intgr acPr an aray of hrctrs (to b prnt most ik) fDon-J a (nt wtr a prcss s on). populr bea vn toug th varibl nms r t rst sh crpti may bliv tt th itt bit of inrmtion cotind i th na maks oin a littl asir2 ug s

µCIOS Whn yo gt to the dicsion of ratim oprting sstms in Captr 6 n beo ou miht want t try your hn t sing on of ts sstms o hp ou o tht t CD tht ccompnis ts book hs o am µC!S p "=. t  on t D wth the pe rssion of Jn L who rte th sste You ar  to us µCI a a stu tool b yu m no e it r a ommrcial product witot prmision om Mr Labrs. µ/  NOT "RWR  insing provisions r µC ar shon on pg   inrmation n Chptrs 6 an 7 n n bl 1 shoud gt yo strt us this systm f o wan mor inrmtion abot t sstm s Mr Lbrosse s book list in t sction on Furtr Ring or go to th µCIS µCIS 2. The Hungarian sed n th book i atualy a dc, o q  gn onvenon he maj dieene beween he daet and the gna ae (1)  ona do not e an undeoe o epaate a ex o the ret of  h aae nae ad 2 the dae e  onnon to nae nton a we as vaab.

µCI OS Licensing nrmation µ/ soce nd objec code cn be eely ditribued (o udt) b acrdit

coge and unveiie wihou equn  lcene,  lon  thee  no commcl ppcon noed. In ohe wod no cenin  eued f µI  ued  educio ue You t obtain n Obec Code Dbuon Lcene to embed µI in  comec oduc Th   cene o u µI in  poduc h  od wh the nen o ke a pot hee wi be  cene ee  uch iuon, nd you need o contt M. Lboe  picn You us obtn  Souce Code Dtbution Lcene o dtibute µI ouc code Aan hee i  fe  uh  icene nd ou need t conct  boe  picin You n conct Jen Lboe : eanLboe@uCOS-Icom o en  boe 94 Cetiew Cice Weon FL 33327 USA l952172036 phone

-95-27-237 (fx)

Web site a wwwucos-iicom You can conact M Labosse r suppo of µC/OS, but pleae do not.do his unti yo have checked he IOS Web sie  he aest vesions and xes Th eampe pogrms on the CD and /OS are inended  use wih he Boad I++ compie  DOS. You can ge he "schoar edion o ths comple (agan  stdy use no r use in deveoping a commeia product)  $49 95 as o his wiing Various eaies carry i o you can conac Boad at wwwbondcom

A First Look at Enbddd Systes

As microprocessors have become sallr and cheaper, more and more prod ucts have microprocessors "embedded in them to make hm smart. Such poucts as VCRs dgtal watches elevators, automobile engines thermostats ndustral ontrol equipment and scientic and medical nstruments are riven by thee micopocessors and their soware People use the term embedded system to mean any computer system hdden in any of these products Soware r embedded systems must hande ay problems beond those und in appcation sowre  desktop or mainame computes Embedded systems oen have several hings to do at once They must espod o external events· (eg, someone pushes an elevator button) They must cope with al unusual conditions without uman interventon Ther work is subject to dadlines

1.1

Examples

of Embedde

Systems

o undersand the issues of embedded-systems soware and to make he pob lems a litle more concrete, let's start by examining a few smple systems Wel look back at these examples om tme to time as we dscuss specc issues and specic slutions

Telegraph The rst sysem that we wll udy is one that was codenmed Teegrph during is development Telegraph alows you o connect a printe that has ony a highspeed serial port   ework From the outside Telegraph i a le

2

A FIRST LOOK  EMBDDD Y

Figure

1.

Telegaph

Prner connecor Netwok connecto

 astc box, 2 to 3 nces on a sde and abou af an nc tck. A  gta cabe on one sde of e box ugs nto te sea ot on te n� A conneco on e oe sde of e box ugs no e newok A se of eega s sown n gue gue  Obvousy ega mus eceve daa om e new0k and coy  ono e sea o Howeve Teega s ae moe comcaed an at ee ae jus a few tngs tat Teega must do: 

I





n  newok dta soemes ave ou of ode daa sometmes ge os ong e w and oe of te daa sommes ave wce Teega mus so o e caos on e newok and vde a cen daa seam o e ne T ee mgt mgt be os of comutes on e newo1k a of wc gt wan o nt at once e nte exects o be ugged no a snge come Teega mus feed e nte one n jo at a me and someow od o a te ote comutes Neok ne ms ovde staus nmaon o any comute on e netok  equest t eve  ey ae busy nng a ob  some oe omue e ogna se-o ne can' do a Teega as o ea as o wok w a numbe of deen tyes of nes wto cstome conguato;eega as o be abe o gue out te knd of ne o wc  s aaced

Tlgraph ws buit o wok wh App nj pne, whch  pcy hd a r por h yo ould onn diec to a Mcosh 1.