c im chung ca H iu hnh

Ngun gc ra i ca h iu hnh l m nhim vai tr trung gian tng tc trc tip vi phn cng ca my tnh, phc v cho nhiu ng dng a dng. Cc h iu hnh cung cp mt tp cc chc nng cn thit cho php cc gi phn mm iu khin phn cng my tnh m khng cn phi can thip trc tip su. H iu hnh ca my tnh c th thy n bao gm cc drivers cho cc ngoi vi tch hp vi my tnh nh card mn hnh, card m thanh... Cc cng c qun l ti nguyn nh b nh v cc thit b ngoi vi ni chung. iu ny to ra mt giao din rt thun li cho cc ng dng v ngi s dng pht trin phn mm trn cc nn phn cng c. ng thi trnh c yu cu v hiu bit su sc v phn cng v c th pht trin da trn cc ngn ng bc cao.

H thng iu hnh bn cht cng l mt loi phn mm nhng n khc vi cc loi phn mm thng thng. S khc bit in hnh l h thng iu hnh c np v thc thi u tin khi h thng bt u khi ng v c thc hin trc tip bi b x l ca h thng. H thng iu hnh c vit phc v iu khin b x l cng nh cc ti nguyn khc trong h thng bi v n s m nhim chc nng qun l v lp lch cc qu trnh s dng CPU v cng chia s ti nguyn.

Kin trc H iu hnh

H iu hnh cho cc h thng nhng - h iu hnh thi gian thc

Thi gian thc (Real - Time) l g?

Thi gian thc rt kh nh ngha. tng c bn ca thi gian thc th hin ch: mt h thng phi c nhng phn ng thch hp, ng thi im vi mi trng ca n. Nhiu ngi lun ngh rng, thi gian thc c ngha l thc s nhanh, cng nhanh cng tt, iu ny l sai lm. Thi gian thc c ngha nhanh (fast enough) trong mt ng cnh, mt mi trng m h thng ang hot ng. Khi chng ta cp n my tnh iu khin ng c t, chng ta cn n chy cng nhanh cng tt.

Mt v d khc, khi chng ta cp n mt nh my lc du ho hc chng hn, nh my c iu khin bi mt hoc mt h thng my tnh. Cc my tnh ny c trch nhim iu khin qu trnh ho hc ng thi phi pht hin ra c cc s c c th xy ra. Tuy nhin, cc phn ng hay cc qu trnh ho hc thng c hng s thi gian kh ln t hng giy cho ti hng pht l t. Chnh v th my chng ta c th gi thit rng my tnh hon ton c kh nng phn ng li cc s c nghim trng. Tuy nhin, t vn l nu h thng my tnh ang trong qu trnh in mt bn bo co di v cc thng s sn lng ca tun trc th t nhin trc trc xy ra. Vy th n mt bao nhiu thi gian c th phn ng li cc s c nh th?

Thc cht ca vic tnh ton thi gian thc khng ch vic phn ng nhanh m cn phi ng tin cy v chnh xc. My tnh iu khin ng c trong t ca bn phi c th iu chnh lung nhin liu v thi gian nh la mt cch hp l trong mi vng quay. Nu khng, ng c s khng lm vic theo mong mun. My tnh trong nh my lc du phi c th pht hin v phn ng li cc iu kin bt thng trong thi gian cho php c th trnh c cc thm ho c th xy ra.

Nh vy, ngh thut ca lp trnh thi gian thc chnh l vic thit k h thng sao cho n c th tip nhn mt cch chnh xc cc rng buc v mt thi gian trong sut qu trnh cc s kin ngu nhin v khng ng b xy ra.

Cc dng thi gian thc

V c bn, chng trnh c tnh thi gian thc phi c kh nng phn ng li cc s kin trong mi trng m h thng lm vic trong khong thi gian nht nh cho trc. Nhng h thng nh vy c gi l h thng iu khin s kin (hay h thng li s kin event-driven) v c th c m t bng thi gian tr t khi m s kin xy ra cho ti khi h thng c hot ng phn ng li vi s kin .

Thi gian thc, mt khc, i hi mt gii hn cao hn v thi gian tr, c gi l thi hn lp danh mc (scheduling deadline). Mt h thng thi gian thc c th c chia lm 2 loi: thi gian thc cng (hard real-time) v thigian thc mm (soft real-time). Trong h thng hard real-time, h thng phi tip nhn v nm bt c scheduling deadline ca n ti mi v mi thi im. S sai st trong vic tip nhn deadline c th dn n hu qu nghim trng thm ch cht ngi. Ly v d: my h tr nhp tim cho bnh nhn khi phu thut. Thut ton iu khin ph thuc vo thi gian nhp tim ca ngi bnh, nu thi gian ny b tr, tnh mng ca ngi bnh s b nh hng.

i vi khi nim soft real-time, scheduling deadline c d th hn cht t. Chng ta mong mun h thng phn ng li cc s kin trong thi gian cho php nhng khng c g thc s nghim trng xy ra nu h thng thnh thong b tr. Li v mt thi gian c th ch n gin l dn n hu qu gim tin cy ca i tng i vi h thng m khng c hu qu th thm no khc xy ra. Mng li thu ngn t ng ca ngn hng l v d r nht cho soft real-time. Mng rt tin t ng ATM l h thng thi gian thc? Chng ai dm t cc c. Khi bn a th ATM vo my, bn mong l my s phn ng li trong vng 1 hay 2 giy. Nhng nu n lu hn th, iu ti t nht c th xy ra l bn st rut v thy kh chu i vi ci my .

Trn thc t c rt nhiu h thng phi hp c 2 loi trn, trong , mt phn no ca h thng lm vic da trn hard real-time, mt s phn khc li da trn soft real-time.

H iu hnh thi gian thc.

H iu hnh thi gian thc RealTime Operating Systems(RTOS), l phn mm iu khin chuyn dng thng c dng trong nhng ng dng in ton nhng c ti nguyn b nh hn ch v yu cu ngt ngho v thi gian p ng tc thi, tnh sn sng cao v kh nng t kim sot mt cch chnh xc.

C th tm thy RTOS bt k ni no. Chng cng ph bin nh nhng h iu hnh m bn quen thuc nh Windows, Mac OS v Unix. RTOS m thm lm vic bn trong cc b nh tuyn v chuyn mch trn mng, ng c xe, my nhn tin, in thoi di ng, thit b y t, thit b o lng v iu khin cng nghip v cc v s ng dng khc.

Mt thuc tnh quan trng ca RTOS l kh nng tch bit vi ng dng, v vy nu c mt chng trnh b "cht" hay hot ng khng hp l, RTOS c th nhanh chng c lp chng trnh ny, kch hot c ch phc hi v bo v cc chng trnh khc hay chnh bn thn h iu hnh khi cc hu qu ca cc lnh sai. C ch bo v tng t cng c p dng trnh tnh trng trn b nh do bt k chng trnh no gy ra. RTOS xut hin hai dng: cng v mm. Nu tnh nng x l ng vi mt s kin no khng xy ra hay xy ra khng nhanh, RTOS cng s chm dt hot ng ny v gi khng gy nh hng n tin cy v tnh sn sng ca phn cn li ca h thng.

V RTOS v my tnh nhng tr nn ph bin trong cc ng dng quan trng, cc nh pht trin thng mi ang to nn nhng RTOS mi vi tnh sn sng cao. Nhng sn phm ny c mt thnh phn phn mm chuyn dng lm chc nng cnh bo, chy cc chng trnh chn on h thng gip xc nh chnh xc vn trc trc hay t ng chuyn i sang h thng d phng. Hin thi RTOS sn sng cao h tr bus Compact PCI ca t chc PCI Industrial Computer Manufacturers Group, bus ny dng cho phn cng c th trao i nng.

RTOS c rt nhiu dng. Sn phm thng mi nh VxWorks v VxWorks AE, u ca Wind River Systems Inc; VxWorks AE c thit k vi tnh sn sng cao, h tr kh nng gi thng ip phn tn v c th chu li. RTOS cho php lp trnh vin tch bit th vin dng chung, d liu v phn mm h thng cng nh ng dng.

LynxOS l loi RTOS cng, lm vic vi Unix v Java. QNX chy trn b x l Intel x86 vi nhn ch c 10 KB.

RTOS ca gii nghin cu gm c Chimera ca i hc Carnegie Mellon. y l h thng a nhim, a b x l thi gian thc, c thit k to s d dng cho cc nh lp trnh trong vic ti cu hnh v ti s dng m. Chimera nhm vo cc h thng r b v t ng. RTOS ca i hc Maryland, c tn l Maruti, h tr cho c ng dng thi gian thc cng v mm.

Trong nhiu nm, ng dng da trn RTOS ch yu l trong cc h thng nhng v mi gn y th chng c mt khp ni, t thit b y t c iu khin bng my nh cho n my pha c ph, nhng ng dng tnh ton phn tn ang thc y cc nh pht trin h iu hnh thc hin nghin cu v pht trin chun. Chnh ph M cng c mt s chng trnh v lnh vc ny nh cng ngh qun l ti nguyn thi gian thc, mng, qun l d liu v phn mm iu khin trung gian. Mc ch ca chng trnh l lm cho cc h thng cng tc, phn tn c th giao tip v chia s ti nguyn vi nhau. Mt u ban chuyn trch ang y mnh vic to ra khung cng ngh cho tnh ton phn tn thi gian thc, p dng cho c ng dng qun s v thng mi. Khung cng ngh ny s h tr cc giao tip v thnh phn lin tc chun.

Cho d ai l ngi to ra mi trng tnh ton phn tn thi gian thc, ph dng th RTOS vn s l mt trong nhng cng ngh quan trng nht m ngi dng cui cha tng nghe n.

So snh kin trc RTOS v OS chun

H thng iu hnh vi phn li l ht nhn phi m nhim cc tc v chnh nh sau:

X l ngt

Lu tr ng cnh chng trnh ti thi im xut hin ngt

Nhn dng v la chn ng b x l v phc v dch v ngt

iu khin qu trnh

To v kt thc qu trnh/tc v

Lp lch v iu phi hot ng h thng

nh thi

iu khin ngoi vi

X l ngt

Khi to giao tip vo ra

Cu trc H iu hnh thi gian thc

Ty theo c ch thc hin v xy dng hot ng ca ht nhn ngi ta phn loi mt s loi hnh:

H thng thi gian thc nh: Vi loi ny cc phn mm c pht trin m khng cn c h iu hnh, ngi lp trnh phi t qun l v x l cc vn v iu khin h thng bao gm:

X l ngt

iu khin qu trnh/ tc v

Qun l b nh

Cng ngh a nhim

Mi qu trnh c mt khng gian b nh ring

Cc qu trnh phi c chia nh thnh cc Thread cng chia s khng gian b nh.

Cc dch v cung cp bi ht nhn

To v kt thc qu trnh/ tc v

Truyn thng gia cc qu trnh

Cc dch v v nh thi gian

Mt s cc dch v cung cp h tr vic thc thi lin quan n iu khin h thng