Bluespec-3: Modules & Interfaces. Bluespec: State and Rules organized into modules

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1 Bluespec-3: Modules & Iterfaces Arvid Computer Sciece & Artificial Itelligece Lab Massachusetts Istitute of Techology Based o material prepared by Bluespec Ic, Jauary 2005 February 28, 2005 L09-1 Bluespec: State ad Rules orgaized ito modules module iterface All state (e.g., Registers, FIFOs, RAMs,...) is explicit. Behavior is expressed i terms of atomic actios o the state: Rule: coditio actio Rules ca maipulate state i other modules oly via their iterfaces. February 22, 2005 L07-2 Courtesy of BlueSpec Ic. Used with permissio. 1

2 xample 1: simple biary multiplicatio typedef bit[15:0] Ti; typedef bit[31:0] Tout; module mkmult0 (mpty); Ti d_iit = 9, r_iit = 5; Replace it by a start method // compile-time costats Reg#(Tout) product <- mkreg (0); Reg#(Tout) d <- mkreg ({16 h0000, d_iit}); Reg#(Ti) r <- mkreg (r_iit); State rule cycle (r!= 0); if (r[0] == 1) product <= product + d; d <= d << 1; r <= r >> 1; edrule: cycle Replace it by a result method rule doe (r == 0); $display ( Product = %d, product); edrule: doe Behavior This module has o iterface methods; it oly multiplies 9 by 5! edmodule: mkmult0 February 22, 2005 L07-3 xample 1: Modularized iterface Mult_ifc; method Actio start (Ti, x, Ti y); method Tout result (); editerface module mkmult1 (Mult_ifc); Reg#(Tout) product <- mkreg (0); Reg#(Tout) d <- mkreg (0); Reg#(Ti) r <- mkreg (0); rule cycle (r!= 0); if (r[0] == 1) product <= product + d; d <= d << 1; r <= r >> 1; edrule: cycle State Behavior method Actio start (d_iit, r_iit) if (r == 0); d <= d_iit; r <= r_iit; edmethod Iterface method result () if (r == 0); retur product; edmethod February edmodule: 22, 2005 mkmult1 L07-4 2

3 Iterfaces iterface Mult_ifc; method Actio start (Ti x, Ti y); method Tout result(); editerface module mkmult1 (Mult_ifc); edmodule A iterface declaratio defies a iterface type Correspods, roughly, to the port list of a RTL module Cotais prototypes of methods, which are trasactios that ca be ivoked o the module A module declaratio specifies the iterface that it implemets (a.k.a. provides) February 22, 2005 L07-5 A Test bech for xample 1 module mktest (mpty); Reg#(it) state <- mkreg(0); Mult_ifc m <- mkmult1(); rule go (state == 0); m.start (9, 5); state <= 1; edrule rule fiish (state == 1); $display ( Product = %d, m.result()); state <= 2; edrule edmodule: mktest Istatiatig the mkmult module Ivokig mkmult s methods February 22, 2005 L07-6 3

4 Module ad iterface istatiatio module mktest (mpty) ; Reg#(it) state <- mkreg(0); Mult_ifc m <- mkmult1(); edmodule Modules istatiate other modules Just like istatiatig primitive state elemets like registers Stadard module-istatiatio shorthad: This: Mult_ifc is shorthad for: Mult_ifc m(); mkmult1 mult_ist(m); module mkmult1 (Mult_ifc); edmodule m <- mkmult1(); (iterface istatiatio) (module istatiatio) February 22, 2005 L07-7 Methods are ivoked from rules module mktest (mpty) ; Mult_ifc m <- mkmult1(); rule go (state==0); m.start(9,5); state <= 1; edrule edmodule module mkmult1 (Mult_ifc); method Actio start (x, y) if (r == 0); d <= x; r <= y; edmethod edmodule Rule coditio: state==0 && r==0 Cojuctio of explicit (state==0) ad implicit (r==0) coditios Rule actios: state<=1, d<=9 ad r<=5 Thus, a part of the rule s actio is i a differet module, behid a method ivocatio February 22, 2005 L07-8 4

5 Three Method Forms BSV method calls look like fuctio ad procedure calls: Value methods: Fuctios which take 0 or more argumets ad retur a value x = m.result() Actio methods: Procedures which take 0 or more argumets ad perform a actio m.start(x) Actiovalue methods: Procedures which take 0 or more argumets, perform a actio, ad retur a result. x <- m.pop() Value methods ca be called from ay expressio but actio or actiovalue methods ca be called oly from a rule or a method body (ot from a rule or method predicate) February 22, 2005 L07-9 Methods as ports Iterface method types ca be iterpreted directly as I/O wires of a module: Argumets are iput sigals Retur values are output sigals A implicit coditio is a output ready sigal A Actio type (side-effect) idicates a icomig le sigal February 22, 2005 L

6 Methods as ports: Mult_ifc iterface Mult_ifc; method Actio start (Ti x, Ti y); method Tout result (); editerface start: 16-bit argumets has side effect (actio) result: o argumet 32-bit result o side effect j == 0 j == start result Mult_ifc module February 22, 2005 L07-11 Methods as ports: FIFO iterface iterface FIFO #(type t); method Actio eq(t); // equeue a item method Actio deq(); // remove oldest etry method t first(); // ispect oldest item method Actio clear(); // make FIFO empty editerface: FIFO ot full ot empty eq deq FIFO module = # of bits eeded to represet the values of type t ot empty first clear February 22, 2005 L

7 Methods as ports: summary Methods ca be viewed as a higher-level descriptio of ports: A method groups related ports together e.g., data_i, RDY ad NABL forces the micro-protocol Called oly whe ready Strobes data at the right time ad more It is easy to relate the geerated Verilog to the BSV source: Trasparet traslatio from methods to ports February 22, 2005 L07-13 Sytax ote: <- <- is used i two ways: Module istatiatio shorthad Ivokig a ActioValue method Queue#(it) q <- mkqueue; rule r1 (); x <- q.pop(); edrule These two uses are distiguished by cotext February 22, 2005 L

8 Two uses of <- I both uses, the operator Has a side-effect istatiate a module discard a elemet from the FIFO Ad returs a value retur the iterface retur the discarded FIFO elemet I oe case these happe durig static elaboratio I the other case these happe dyamically (durig HW executio) February 22, 2005 L07-15 Sharig methods February 22, 2005 L

9 A method ca be ivoked from more tha oe rule module mktest (); FIFO#(it) f <- mkfifo(); rule r1 ( cod1 ); f.eq ( expr1 ); edrule rule r2 ( cod2 ); f.eq ( expr2 ); edrule edmodule: mktest iterface FIFO#(type t); Actio eq (t ); editerface module mkfifo (); method eq (x) if ( otfull ); edmethod edmodule: mkfifo (I geeral the two ivokig rules could be i differet modules) February 22, 2005 L07-17 Sharig methods I software, to call a fuctio/procedure from two processes just meas: Create two istaces (usually o two stacks) A BSV method represets real hardware There is oly oe istace (per istatiated module) It is a shared resource Parallel accesses must be scheduled (cotrolled) Data iputs ad outputs must be muxed/ distributed The BSV compiler iserts logic to accomplish this sharig This logic is ot a artifact of usig BSV it is logic that the desiger would otherwse have to desig maually February 22, 2005 L

10 Sharig a method The compiler iserts logic for sharig a method r1 cotrol r2 DATA_IN NAB ot full RDY NAB ot empty RDY DATA_OUT ot empty RDY eq deq first FIFO February 22, 2005 L07-19 Importat special cases Value methods without argumets eed o muxig or cotrol, sice they have o iputs ito the module xamples: r._read for a register f.first for a FIFO Note: these methods are combiatioal fuctios, but they deped o the module s iteral state (Advaced topic) BSV primitives ca specify a replicatio factor for certai methods, so two calls to the same method actually get coected (automatically) to differet replicas of the method.g., a read method of a multi-ported register file February 22, 2005 L

11 Iterface variatios It is the desiger s choice how to expose the fuctioality of a module usig iterface methods.g., a FIFO ca have several iterfaces February 22, 2005 L07-21 A FIFO iterface iterface FIFO #(type t); method Actio eq(t); // equeue a item method Actio deq(); // remove oldest etry method t first(); // ispect oldest item method Actio clear(); // make FIFO empty editerface: FIFO ot full ot empty eq deq FIFO module = # of bits eeded to represet the values of type t ot empty first clear February 22, 2005 L

12 Aother FIFO iterface: Combie first & deq iterface FIFO #(type t); method Actio push(t); // equeue a item method ActioValue#(t) pop(); // remove oldest etry method t first(); // ispect oldest item method Actio clear(); // make FIFO empty editerface: FIFO ot full ot empty ot empty push pop first FIFO module may or may ot provide first method clear February 22, 2005 L07-23 FIFOF: xplicit ready sigals The desiger might wat to expose the implicit ready sigals the otfull ad otmpty sigals: iterface FIFOF#(type atype); eq first deq clear method Bool otfull(); method Bool otmpty(); editerface The origial eq/deq/first methods may or may ot be protected by implicit coditios, depedig o the module implemetatio February 22, 2005 L

13 Modularizig your desig Cosider a speculative, out-of-order microachitecture Register File Fetch FIFO Decode Brach FIFO Re- Order Buffer (ROB) FIFO FIFO FIFO FIFO ALU Uit MM Uit FIFO FIFO FIFO FIFO Istructio Memory Suppose we wat to focus o the ROB module Data Memory February 22, 2005 L07-25 ROB actios Get operads for istr Register File Re-Order Buffer Writeback results State Istructio Operad 1 Operad 2 Result mpty Waitig W Dispatched Di Killed K Doe Do Decode Uit Isert a istr ito ROB Head Tail W W W Istr A V 0 V 0 - Istr B V 0 V 0 - Istr C V 0 V 0 - W Istr D V 0 V 0 - Get a ready ALU istr Put ALU istr results i ROB ALU Uit(s) Resolve braches Get a ready MM istr Put MM istr results i ROB MM Uit(s) February 22, 2005 L

14 Modularizig your desig A atural orgaizatio for two modules may be recursive. Module A Module B but ufortuately BSV does ot hadle recursive module calls... February 22, 2005 L07-27 A rule that calls a method ca be tured ito a method module modulea (IterfaceA); rule foo(true); MsgTypeB msg <- modb.getmessage(); <use msg> edrule edmodule: modulea Module A module ModuleA (IterfaceA); rule method foo(msgtypeb msg); <use msg> edmethod edmodule: modulea Module A February 22, 2005 L

15 Alterative Modularizatio Put oe module iside the other Module A rules Module B Create a ew module ad put both modules iside it. Provide rules to pass values ibetwee Module C Module A rule rules Module B February 22, 2005 L07-29 Glue module code... module mktest (mpty); IterfaceA moda <- mkmodulea(); IterfaceB modb <- mkmoduleb(); rule messagefromatob (True); MsgTypeA msg <- moda.getmessagetob(); modb.hadlemessagefroma(msg); edrule rule messagefrombtoa (True); MsgTypeB msg <- modb.getmessagetoa(); moda.hadlemessagefromb(msg); edrule edmodule: mktest February 22, 2005 L

16 Modular orgaizatio: Two Stage Pipelie imem RFile rf FIFO bu dmem fetch & decode pc set pc execute Read method call Actio method call February 22, 2005 L07-31 Summary A iterface type (e.g., Mult_ifc) specifies the prototypes of the methods i such a iterface The same iterface ca be provided by may modules Module defiitio: A module header specifies the iterface type provided (or implemeted) by the module Iside a module, each method is defied Ca cotai implicit coditios, actios ad retured values May module defiitios ca provide the same iterface Module use: A iterface ad a module are istatiated Iterface methods ca be ivoked from rules ad other methods Method implicit coditios cotribute to rule coditios Method actios cotribute to rule actios rule sematics exteds smoothly across module boudaries February 22, 2005 L