6.175: Constructive Computer Architecture. Oct 7,

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1 6.175: Costructive Computer Architecture Tutorial 2 Advaced BSV Qua Nguye (Now uses the correct dates o PPT slides) T02-1 Admiistrivia Today is add date! Please test vlsifarm machies Remaiig labs schedule posted Labs will become more difficult startig ext week Office hours poll T01-2

2 Outlie Schedulig ad EHRs Sythesis Boudaries Typeclasses ad Provisos T01-3 EHRs ad Schedulig Desig example Up/dow couter iterface Couter; Bit#(8) read; Actio icremet(bit#(8) x); Actio decremet; editerface T01-4

3 Review: EHR coflict matrix EHR.r0 EHR.w0 EHR.r1 EHR.w1 EHR.r0 CF < CF < EHR.w0 > C < < EHR.r1 CF > CF < EHR.w1 > > > C T01-5 Up/Dow Couter Coflict Desig module mkcouter( Couter ); Reg#(Bit#(8)) cout <- mkreg(0); method Bit#(8) read; retur cout; method Actio icremet(bit#(8) x); cout <= cout + x; method Actio decremet; cout <= cout 1; edmodule icremet coflicts with decremet T01-6

4 Cocurret Desig: A geeral techique 1. Replace coflictig registers with EHRs 2. Choose a order for the methods 3. Assig ports of the EHR sequetially to the methods depedig o the desired schedule Method described i paper that itroduces EHRs: The Ephemeral History Register: Flexible Schedulig for Rule-Based Desigs by Daiel Rosebad T01-7 Up/Dow Couter Cocurret desig: read < ic < dec module mkcouter( Couter ); Ehr#(3, Bit#(8)) cout <- mkehr(0); method Bit#(8) read; // use port 0 retur cout[0]; method Actio icremet(bit#(8) x); // use port 1 cout[1] <= cout[1] + x; method Actio decremet; // use port 2 cout[2] <= cout[2] 1; edmodule We could use Ehr#(2, Bit#(8)), but ot ecessary. T01-8

5 Coflict-free desigs: tl;dr 1. Create EHRs that represet calls to Actio ad ActioValue methods 2. Create a caoicalize rule that hadles these requests 3. Reset EHRs 4. Limit each method to oe call T01-9 Coflict-Free Desig A geeral techique 1. Replace coflictig Actio ad ActioValue methods with writes to EHRs represetig method call requests If there are o argumets for the method call, the EHR should hold a value of Bool If there are argumets for the method call, the EHR should hold a value of Maybe#(Tuple2#(TypeArg1,TypeArg2)) or somethig similar 2. Create a caoicalize rule to hadle all of the method call requests at the same time 3. Reset all the method call request EHRs to False or tagged ivalid at the ed of the caoicalize rule 4. Guard method calls with method call requests If there is a outstadig request, do t allow a secod oe to happe T01-10

6 Up/Dow Couter Coflict-Free desig methods module mkcouter( Couter ); Reg#(Bit#(8)) cout <- mkreg(0); Ehr#(2, Maybe#(Bit#(8))) ic_req <- mkehr(ivalid); Ehr#(2, Bool) dec_req <- mkehr(false); // caoicalize rule o ext slide method Bit#(8) read = cout; method Actio icremet(bit#(8) x) if(!isvalid(ic_req[0])); ic_req[0] <= Valid (x); method Actio decremet if(!dec_req[0]); dec_req[0] <= True; edmodule T01-11 Up/Dow Couter Coflict-Free desig caoicalize rule module mkcouter( Couter ); // Reg ad EHR defiitios o previous slide rule caoicalize; let cout_xt = cout; if(isvalid(ic_req[1])) cout_xt = cout_xt + frommaybe(?, ic_req[1]); if(dec_req[1]) cout_xt = cout_xt - 1; cout <= cout_xt ic_req[1] <= Ivalid; dec_req[1] <= False; edrule // methods o previous slide edmodule Spoiler alert: This is basically the solutio to Lab 4. T01-12

7 Sythesis Boudary Module without sythesis boudary Methods are ilied Pros: Aggressive guard liftig (if else ) Cos: log compile time if istatiated may times Module with sythesis boudary (* sythesize *) Module mkmymodule( MyModuleIFC ); The module will be compiled separately The module becomes a black box Pros: shorter compile time, o iliig Cos: coservative guards T01-13 Sythesis Boudary Guard Logic (Example) Sythesis boudaries simplifies guard logic method Actio doactio( Bool x ); if( x ) begi <a> whe p; ed else begi <a> whe q; ed Lifted guard without sythesis boudary: (!x g(p)) && (x g(q)) Lifted guard with sythesis boudary: (p && q) Sythesis boudaries do ot allow iputs to be i guards. There are other restrictios T01-14

8 Sythesis Boudary A sythesis boudary ca oly be placed over a module with: No type parameters i its iterface No parameters i the module s costructor that ca t be coverted to Bits (o iterfaces ca be passed i) Takeaways Sythesis boudary may affect guard & schedulig Faster compilatio T01-15 Typeclass Motivatig example: parametrized add fuctio t adder(t a, t b); retur a + b; edfuctio Some type t ca be added: Bit#(), It#() Some caot: eum, struct, tagged uio Typeclass If a type blogs to a typeclass, the certai operatios ca be performed o this type Typeclass Arith: +, -, *, /, %, egate Typeclass Bits: pack, upack T01-16

9 Typeclass Defie a typeclass typeclass Bits#(type a, umeric type ); fuctio Bit#() pack(a x); fuctio a upack(bit#() x); edtypeclass If types a ad are i typeclass Bits, the we ca do pack & upack with them T01-17 Istace Types are added to typeclasses by creatig istaces of that typeclass typedef eum { Red, Gree, Blue } Color derivig (Eq); // o derivig(bits) istace Bits#(Color, 2); fuctio Bit#(2) pack(color x); retur x==red? 3 : x==gree? 2 : 1; edfuctio fuctio Color upack(bit#(2) x); retur x==3? Red : x==2? Gree : Blue; edfuctio edistace Keyword derivig: do above process i a default way T01-18

10 Provisos Tell compiler that type t ca do + Add provisos (compile error without provisos) fuctio t adder(t a, t b) provisos(arith#(t)); retur a + b; edfuctio Provisos Tell compiler additioal iformatio about the parametrized types Compiler ca type check based o the ifo T01-19 Typeclass Takeaway Typeclasses allow polymorphism across types Provisos restrict modules type parameters to specified type classes Typeclass Examples (BSV Referece guide Sectio B.1) Eq: ==,!= Ord: <, >, <=, >=, mi, max, compare Bits: pack, upack Arith: +, -, *, /, %, egate Literal: fromiteger, iliteralrage FShow: fshow (format values icely as strigs) T01-20