Robustness of Evolvable Hardware in the Case of Fault and Environmental Change

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1 Proeedings of the IEEE Interntionl Conferene on Rootis nd Biomimetis Deemer -,, Guilin, Chin Roustness of Evolvle Hrdwre in the Cse of Fult nd Environmentl Chnge Jin Gong, Mengfei Yng Astrt The ontroller of root or stellite is primrily implemented with eletroni iruit. However, the ontroller iruit is vulnerle in the spe. Fults nd hnging environment re two min ftors tht use filure of the ontroller iruit. In order to survive in suh hrsh irumstnes, n evolvle hrdwre method is used. In this pper, the roustness of evolvle hrdwre is nlyzed in the se of fult nd environmentl hnge y mens of modeling. Additionlly, iruit evolution experiment with four senrios is performed, whih shows the roustness of evolvle hrdwre in the two ses. I. INTRODUCTION HE ontroller is the kernel of root or stellite, whih Tgthers informtion from sensors nd ontrol the exeutive mehnism y mens of ontrol lgorithms. However, the ontroller implemented with eletroni iruits is vulnerle in the spe. An evolvle hrdwre method ws used in root ontroller more thn ten yers go []. In suh ritil pplitions, the evolving iruit is not only fult tolernt ut lso dptive to the environment. But how the iruit n survive in the se of fult nd environmentl hnge should e further disussed. Mny reserhers study fult tolerne nd dpttion of evolvle hrdwre. A. Thompson studied the reltionship etween muttion opertor of evolution lgorithm nd stuk-t fult of hrdwre, presenting fult tolerne of evolvle hrdwre with experiment []. A. M. Tyrrell presented tht stti redundny ws used in trditionl fult tolerne, while dynmi redundny ould e quired in evolving proess [][]. Moreover, he studied widely the iology inspired fult tolerne systems []. T. Arsln designed filters in evolvle hrdwre pltform, implementing roust iruit when fults over 5% re of the iruit [5]. P. C. Hddow presented tht future extremely hrsh nd hnging environment need lrge omplex iruit with fult tolerne, so tht he studied roust evolvle hrdwre tehnologies in XILINX 6 series FPGA [6]. D. Keymeulen nd A. Stoi et l of JPL developed dptive fult tolernt systems for spe pplitions, mnufturing kind of progrmmle devie lled field progrmmle Mnusript reeived July 6,. Jin Gong is Ph.D. student with the Beijing Institute of Control Engineering, Beijing, P.R.Chin (phone: ; e-mil: gjxjtu7@hotmil. om). Mengfei Yng is professor with the Chin Ademy of Spe Tehnology, Beijing, P.R.Chin. (e-mil: yngmf@ie.org.n). trnsistor rry (FPTA) [7][]. The survivl experiment of evolvle iruit in extreme temperture nd rdition environment is performed in [][]. However, there is nother onept of environment, whih refers to the environmentl requirement tht iruit should stisfy []-[]. This is just like the retures tht should dpt to the nturl environment. A. M. Tyrrell nd A. Stoi pointed out tht iruit should hve dptility to meet the hnging requirement of environment [][]. X. Yo nd T. Higuhi, erly reserhers from Jpn, presented mny prolems in evolvle hrdwre reserh []. Among these prolems, dpttion of system is n importnt reserh re. In this pper, we disuss the roustness of iruit in the se of fult nd environmentl hnge. The rest of this pper is orgnized s follows. In Setion, iruit evolution proess is nlyzed with modeling fult nd environment. In setion, oth the iruit evolution experiment is exptited, nd the experiment result is disussed. Finlly, the onlusion is drwn in setion. II. CIRCUIT EVOLUTION IN THE CASE OF FAULT AND ENVIRONMENTAL CHANGE. A. Model of fult nd environment Fult is n norml stte of iruit, whih ehves differently in different irumstnes. In order to desrie fult expliitly, fult model is usully used. In this pper, we disuss fults of logil lyer of hrdwre, using fult model to represent tegory of logil fults. The fult model n e stted s follows. Assume the numer of iruit fults is finite, the fult set n e defined s T={t i i=,, m}, where m is the numer of fults. The fult model set n e defined s M={M, M,, M h }, where M j ={t j,, t jl } (j=,, h) is fult model, l is the numer of fults tht eh fult model ontins, h is the numer of fult models. Environment n e onsidered s funtionl requirement. The hnge of environment diretly indues hnge of requirement. In this wy, environment is n equivlent terminology to requirement. Thus, n environment senrio is defined s r i, whih is lso requirement. Assume the numer of requirements is finite, the environment/requirement set n e defined s R={r, r,, r n }, where n is the numer of environments. B. Desription of iruit stte Different iruit hs different funtion, depending on the environment. The iruit funtion set n e defined s U={u, //$5. IEEE.

2 u,, u n }. When there is no fult in the iruit, eh u i onforms to r i, i.e. u i = r i, where i=,, n. The stte (r i, u i ) is norml working stte of the iruit, lled legl stte. The forml desription of stte (r i, u i ) is s follows. Given n environment r i R, there must e unique funtion u i U tht orresponds to r i. Thus, there exists one-to-one mpping f: r i >u i, whih is lso funtion from set R to set U, notted s u i =f(r i )= r i. The stte (r i, u i ) tht stisfies funtion f is legl stte, whih is lso notted s s i =(r i, u i ), i=,, n. All the legl sttes form legl stte set S={s, s,, s n }, where S R U. While the stte (r i, u j ) tht does not stisfy funtion f is n illegl stte of iruit, whih is notted s s i =(r i, u j ), i=,, n, j=,, n, i j. All the illegl sttes form illegl stte set S, where S R U. Assume the universl set of ll the sttes is I=R U, there exists n eqution S I S. A stte in the legl stte set represents iruit without fults, whih is lso stle stte of evolving iruit. While stte in the illegl stte set represents iruit with fults, whih is lso n unstle stte in the evolution. If the iruit is in unstle stte, it must e repired, or it will fil. C. Ciruit stte trnsformtion There re three ftors tht use iruit stte to trnsform, whih re fult, environmentl hnge nd evolution. () By fult: When fult rises (denoted y fult model M i in set M), the iruit funtion will hnge. So, the iruit stte will trnsfer from the stte (r i, u i ) in set S to the stte (r i, u j ) in set S. () By environmentl hnge: When the environment hnges (denoted y trnsformtion from r i in set R to r j in set R), the iruit stte will trnsfer from stte (r i, u i ) in set S to stte (r j, u i ) in set S. () By evolution: We ssume tht the evolution is suessful, for the unsuessful evolution is more omplex prolem, whih is not the sope of this pper. When iruit evolves suessfully, the iruit stte will trnsfer from stte (r i, u j ) or (r j, u i ) in set S to stte (r i, u i ) or (r j, u j ) in set S respetively. As n e seen, iruit stte trnsfers from legl stte to n illegl stte with fult or environmentl hnge. While suessful evolution mkes the illegl stte k to legl stte. In this wy, evolvle hrdwre n quire fult tolerne nd dpttion. The stte trnsformtion is illustrted in figure. From figure, we n see tht the originl iruit stte is (r i, u i ) S, whih mens the iruit is norml. When fult rises, iruit funtion hnges from u i to u j. After suessful evolution, iruit funtion returns to u i. The finl stte is (r i, u i ) S, s it used to e. When environment hnges from r i to r j, the iruit funtion does not hnge. After suessful evolution, iruit funtion hnges to new one u i in order to meet the hnged environment r j. The finl stte is (r j, u j ) S, whih is new stte ompred to the originl stte. Consequently, evolvle iruit is roust in the se of fult nd environmentl hnge. However, the evolution result is different. The evolution in the se of fult mkes iruit reover to the originl stte, whih shows fult tolerne of evolvle hrdwre. While the evolution in the se of environmentl hnge led the iruit to new stte, whih shows dptility of the evolution method. D. Disussion with n exmple In order to explin the iruit evolution in the two ses, we tke simple onfigurle iruit for exmple. The onfigurle iruit is omposed of LUTs (look-up tle), multiplexer nd input/output ports. The min struture of the onfigurle iruit is shown in Figure (). Beuse fult tolerne is quired y mens of redundny, two LUTs re used in the onfigurle iruit. The expeted funtion n e implemented with one LUT, while nother LUT is redundnt for suessful evolution when there re fults in the iruit. The multiplexer deides whih LUT is the output. The inputs of the iruit re nd, output is. X s re onfigurle its tht n e onfigured to it s or it s, so tht the iruit funtion vries ording to the onfigurtion. Mk (ri, uj) X X X X X X () Norml () With fult M () With fult M Fig.. Configurle iruit (norml iruit nd iruit with fults) In order to illustrte the evolutionry fult tolerne nd dptility, two environments, two funtions nd two fults re defined s follows. () Environment r : f (, ) ; () Environment r : f (, ) ( ) ( ) ; () Ciruit funtion u : g (, ) ; () Ciruit funtion u : g (, ) ( ) ( ) ; (5) Fult M is stuk-t- fult of ell of the first LUT, shown in figure (). (6) Fult M is stuk-t- fult of ell of the first LUT, shown in figure (). So, there is n environment set R={r, r }, iruit funtion set U={u, u } nd fult model set M={M, M }. Then, universl set of sttes is I=R U={(r, u ), (r, u ), (r, u ), (r, u )}, legl stte set is S={(r, u ), (r, u )}, illegl stte set is S ={(r, u ), (r, u )}. rj (rj, ui) (rj, uj) Fig.. Ciruit stte trnsformtion in suessful evolution in the se of fult nd environmentl hnge 5

3 Assume tht the iruit is originlly in legl stte (r, u ) or (r, u ). At the originl stte, the output of the iruit is deided y the first LUT. The evolution proess is shown in figure. When fult rises, the stte trnsfers to n illegl stte. Then the iruit mnges to ypss the fult. After suessful evolution, the iruit returns to the originl legl stte, nd the iruit output is deided y the seond LUT. The whole proess is desried s follows. (r, u ) M > (r, u ) > (r, u ), figure (); (r, u ) M > (r, u ) > (r, u ), figure (). When the environment hnges, the stte trnsfers from the originl legl stte to n illegl stte, too. Then the iruit mnges to dpt the new environment. After suessful evolution, the iruit turns to new legl stte, nd the iruit output is still deided y the first LUT (Atully, the iruit output is deided y the seond LUT in some evolution. But it lso shows the dpttion). The whole proess is desried s follows. (r, u ) r > (r, u ) > (r, u ), figure (); (r, u ) r > (r, u ) > (r, u ), figure (d). fult Figure shows the stte trnsformtion of the iruit evolution under fult nd hnging environment. III. EXPERIMENT evolution () fter fult M. fult evolution () fter fult M. evolution () fter environment hnges to r. evolution (d) fter environment hnges to r. (r, u) M r (r, u) (r, u) A. Evolvle hrdwre for experiment In order to verify the former disussion, we design n r M (r, u) Fig.. Stte trnsformtion of exmple iruit. evolvle system for experiment. The system is minly omposed of onfigurle iruit, high performne omputer, evlution logi nd interfe logi. The rhiteture of the evolvle hrdwre system is shown in figure 5. High Performne Computer (Geneti Algorithm nd Fitness Clultion) RS- Communition Interfe logi (implemented with Single Chip Computer) Ciruit Bord Logi for evlution Configurle Ciruit (implemented with RAM) Fig. 5. Therhitetureofevolvle hrdwre system. In the evolvle hrdwre system, the high performne omputer tkes hrge of GA (Geneti Algorithm) nd fitness lultion. By mens of RS- ommunition, the high performne omputer downlods the popultion of GA to the onfigurle iruit, nd uplods the evlution vlues of eh individul of the popultion from the onfigurle iruit. Interfe logi is minly implemented with single hip omputer, in hrge of ommunition nd onfigurtion ontrol. The evlution logi evlutes the output of the onfigurle logi. The onfigurle logi is the key omponent of evolvle hrdwre system, whih implements the trget iruit. The onfigurle iruit hs four inputs X, X, X, X, nd one output Y. The detil of the onfigurle iruit is shown in figure 6. LUT struture is dopted for internl onfigurle rhiteture of the iruit. Moreover, two LUTs re used to provide enough resoure for suessful evolution in the se of stuk-t fult. Eh LUT hs 6 onfigurle its, four input ports nd one output port. A multiplexer is used to deide whih LUT is the output of the entire onfigurle iruit. So, its hromosome represents the onfigurtion of the onfigurle iruit. The onfigurtion of eh LUT is 6 its, nd the multiplexer onfigurtion is it. X X X X LUT LUT 6 its 6 its hromosome: totl: its Fig. 6. Configurle iruit with its hromosome. The evolvle hrdwre system works s follows. Firstly, the high performne omputer genertes initil popultion rndomly. Seondly, the omputer downlods eh individul of the popultion to the onfigurle iruit sequentilly. Thirdly, eh individul is evluted in the onfigurle iruit. Finlly, the omputer uplods evlution vlue of eh individul from the onfigurle iruit, lulting fitness of the individul. After the whole popultion is evluted, the omputer lultes the optimum fitness of the popultion. If optimum fitness is the expeted vlue, the evolution is suessful. Otherwise, the evolution Y 5

4 will go on. B. Geneti lgorithm In the experiment, SGA (Stndrd Geneti Algorithm) is dopted. Binry oding is used for hromosome ode. The mening of the hromosome hs een explined in setion.a. Three GA opertors re used, whih re roulette wheel seletion, one point rossover nd one point muttion. Crossover rte is.. Muttion rte is.. Popultion size is. Mximum genertion of the evolution is set to 5 to prevent infinite running of the lgorithm. The onfigurle iruit hs four inputs, so tht the numer of inputs omintions is 6. The expeted output for eh inputs omintion is stored in the system. If the runtime output of the onfigurle iruit is equl to the expeted output, the fitness fit l (l=,, 6) is set to, otherwise fit l is. The fitness of eh individul n e lulted ording to eqution (). The optimum fitness fit op is 6. When the fit of n individul is equl to fit op, the individul is the optimum. 6 fit fit () l C. Experiment setup The trget iruit to evolve is omintionl logi with four inputs nd one output. In order to ompre the evolution in different onditions, four evolution senrios re designed s follows. Senrio : The iruit evolves in norml ondition, i.e. without fult nd environmentl hnge. The evolution trget is Y X X X X, whih is lso the originl environment, notted s r o. Assume the iruit stte is S o, when the evolution suesses. Senrio : The iruit evolves fter stuk-t fult, from norml stte S o. The fult is stuk-t- fult in the first LUT with ddress in the onfigurle rhiteture, whih is implemented y mens of fult injetion. Senrio : The iruit evolves fter environment hnges to r A, from norml stte S o. The environment r A is Y X X X X. The peulirity of r A is imlne distriution of it in the iruit onfigurtion, whih is more different from r o. While, the environment r o hs lne distriution of it in the iruit onfigurtion. Senrio : The iruit evolves fter environment hnges to r B, from stte S o. The environment r B is Y. The onfigurle iruit evolves in the four senrios to verify the roustness of evolvle hrdwre. The men fitness nd terminl genertion of eh evolution run n reflet the roustness of evolvle hrdwre. Assume the numer of experiment runs in eh senrio is T, terminl genertion of eh run is G, the popultion is P, the individul fitness of eh run is ij (i=,, P, i=,, G). The ij is lulted ording to eqution (), ij =fit. Three l prmeters re dopted to ssess the evolution result. () Men fitness of eh evolution run, ording to Eqution (). This prmeter desries how fit the individul funtion is to the environment. G P p (/ G) ((/ P) ), (/ P) () j i ij () Stndrd devition of fitness v, ording to eqution (). This prmeter is more urte desription of the men fitness. j i G j () j v (/ G) ( ) () Terminl genertion of eh evolution run g. This prmeter desries the speed of evolution, while the former two prmeters reflet the fitness in evolution. D. Experiment result In the experiment, runs re performed for eh senrio. All the evolution runs re suessful, so tht the roustness of evolvle hrdwre is verified, whih is shown in figure 7 to figure. Men Fitness Norml (senrio ) (Men to these vlues is.56 ) with Environment hnge ra (senrio ) Men Fitness (Men to these vlues is.6 ) Men Fitness with Fult Injetion (senrio ) (Men to these vlues is.5 ) with Environment hnge rb (senrio ) Men Fitness (Men to these vlues is. ) Fig. 7. Men fitness of evolution in four senrios. Norml (senrio ) with Environment hnge ra (senrio ) Stndrd devition Stndrd devition Stndrd devition Stndrd devition with Fult Injetion (senrio ) with Environment hnge rb (senrio ) Fig.. Stndrd devition of men fitness in four senrios. ij 5

5 Genertions Genertions Norml (senrio ) 6 (Men to these vlues is.7 ) with Environment hnge ra (senrio ) 6 (Men to these vlues is.5 ) Genertions Genertions with Fult Injetion (senrio ) 6 (Men to these vlues is. ) with Environment hnge rb (senrio ) 6 (Men to these vlues is 6.57 ) Fig.. Terminl genertion of evolution in four senrios. Men fitness of eh senrio is shown in figure 7. It n e seen from figure 7 tht the trend of hs no ovious differene mong four senrios. The trend n lso e seen from the generl men vlues ( A s) of ll the runs of eh T senrio, A (/ T). The A is nother prmeter tht t n e used to ompre the differene of fitness in four senrios roughly. The four generl men vlues ( A s) re s follows:.56 in norml evolution senrio,.5 in evolution senrio with fult,.6 nd. in evolution senrios with environmentl hnge to r A nd with environmentl hnge to r B respetively. So, ording the men fitness, the evolutions in four senrios re lmost sme. Stndrd devition of fitness v is shown in figure. The stndrd devition vlues re round in eh senrio, whih lso present no ovious differene mong four evolution senrios. As to the terminl genertion of eh evolution g, the vlues re shown in figure. As n e seen from figure, there is not ovious differene mong four senrios too. The T generl men vlues M (/ T) G t n e used to ompre the differene of evolution speed in four senrios roughly. These generl men vlues ( M s) in four senrio re s follows:.7 in norml evolution senrio,. in evolution senrio with fult,.5 nd 6.57 in evolution senrios with environmentl hnge to r A nd with environmentl hnge to r B respetively. The vlues in figure show the sme evolution speed of evolvle hrdwre in the four senrios. Consequently, the roustness of evolvle hrdwre in the se of fult nd environmentl hnge is verified y the experiment. With enough resoure, the iruit n mnge to survive whtever hppens. Wht is more, the iruit presents lmost the sme roustness in fult nd two kinds of different environmentl hnges. IV. CONCLUSION Orienting the ontroller iruit of root or stellite in spe pplitions, elorte nlysis hs een performed on the roustness of iologil inspired method in the se of fult nd environmentl hnge. Not only the nlysis ut lso the experiment shows tht the iruit n evolve to survive in hrd onditions, presenting fult tolerne nd dptility to environment. Moreover, the evolvle hrdwre presents lmost the sme roustness in different onditions, e.g. fult nd two differene environmentl hnges. However, it hs to e disussed whether more omplex iruit will present sme roustness in different fults nd different environmentl hnges. REFERENCES [] A. Thompson, Evolving fult tolernt systems, in first interntionl onferene on geneti lgorithm in engineering systems: innovtions nd pplitions, IEE, - Sept. 5, pp. 5-5 [] A. M. Tyrrell, G. Hollingworth nd S. L. Smith, ry strtegies nd intrinsi fult tolerne, in Proeedings of the third NASA/DoD workshop on evolvle hrdwre, IEEE, - Jul., pp. -6 [] R. O. Cnhm nd A. M. Tyrrell, Evolved fult tolerne in evolvle hrdwre, in Proeedings of the ongress on evolutionry omputtion, IEEE, vol., -7 My, pp [] W. Brker, D. M. Hllidy, Y. Thom, E. Snhez, G. Tempesti nd A. M. Tyrrell, Fult tolerne using dynmi reonfigurtion on the POEti tissue, IEEE Trns. ry Computtion, vol., no. 5, Ot 7, pp [5] B. I. Hounsell nd T. Arsln, ry design nd dpttion of digitl filters within n emedded fult tolernt hrdwre pltform, in proeedings of the third NASA/DoD workshop on evolvle hrdwre, IEEE, - July, pp. 7-5 [6] P. C. Hddow, P. vn Remortel, From here to there: future roust EHW tehnologies for lrge digitl designs, in proeedings of the third NASA/DoD workshop on evolvle hrdwre, IEEE, - July, pp. - [7] D. Keymeulen, R. S. Zeulum, Y. Jin nd A. Stoi, Fult-tolernt evolvle hhrdwre using field-progrmmle trnsistor rrys, IEEE Trns. Reliility, vol., no., Sept., pp. 5-6 [] A. Stoi, T. Arsln, D. Keymeulen, Vu. Duong, R. Zeulum, I. Ferguson nd T. Dud, ry reovery from rdition indued fults on reonfigurle devies, in proeedings of erospe onferene, vol., 6- Mrh, IEEE, pp. -57 [] G. W. Greenwood, On the prtility of using intrinsi reonfigurtion for fult reovery, IEEE Trns. ry Computtion, vol., no., Aug. 5, pp. -5 [] G. S. Hollingworth, A. M. Tyrrell nd S. L. Smith, To evolve in hnging environment, in olloquium on reonfigurle systems, IEE, Mr., pp. 6/-6/5 [] A. Stoi nd R. Andrei, Adptive nd evolvle hrdwre - A multifeted nlysis, in seond NASA/ESA onferene on dptive hrdwre nd systems, IEEE, 5- Aug. 7, pp. 6- [] X. Yo nd T. Higuhi, Promises nd hllenges of evolvle hrdwre, IEEE Trns. Systems, Mn nd Cyernetis-Prt C: Applitions nd Reviews, vol., no., Fe., pp