annotate modules/bluespec/Pygar/lab4/BranchPred.bsv @ 43:4d87fa55a776 pygar svn.44

[svn r44] processor largely working and mixer in good status
author punk
date Wed, 05 May 2010 12:28:07 -0400
parents 74716e9a81cc
children
rev   line source
rlm@8 1 import RegFile::*;
rlm@8 2 import ProcTypes::*;
rlm@8 3 import FIFO::*;
rlm@8 4
rlm@8 5 typedef Maybe#(Addr) BrPred;
rlm@8 6 typedef Bit#(4) BPindx;
rlm@8 7
rlm@8 8 typedef struct {Addr brpc; Addr nextpc;} BrPair deriving (Bits,Eq);
rlm@8 9
rlm@8 10 typedef union tagged
rlm@8 11 {
rlm@8 12 BrPair Valid;
rlm@8 13 void Invalid;
rlm@8 14 } CBranchPath deriving(Bits, Eq); // have the cache start out invalid and add valid values.
rlm@8 15
rlm@8 16 interface BranchPred;
rlm@8 17 method BrPred get(Addr pres); //returns a maybe type that is invalid if no predition
rlm@8 18 method Action upd(Addr pres, Addr next);
rlm@8 19 endinterface
rlm@8 20
rlm@8 21 module mkBranchPred(BranchPred);
rlm@8 22
rlm@8 23 //state variables
rlm@8 24 RegFile#(BPindx, CBranchPath) bcache <- mkRegFileFull(); // cache to hold 16 (based on BPindx)
rlm@8 25
rlm@8 26 method Action upd(Addr pres, Addr next);
rlm@8 27 BrPair brp;
rlm@8 28 brp = BrPair {brpc:pres, nextpc:next};
rlm@8 29 bcache.upd(pres[5:2], tagged Valid brp);
rlm@8 30 endmethod
rlm@8 31
rlm@8 32 method BrPred get(Addr prespc);
rlm@8 33 BPindx rd = prespc[5:2];
rlm@8 34 let cbp = bcache.sub(rd);
rlm@8 35 if (cbp matches tagged Valid .bp &&& bp.brpc == prespc) //make sure that the read value was actually put there and the full address matches
rlm@8 36 return tagged Valid bp.nextpc;
rlm@8 37 else return Invalid;
rlm@8 38 endmethod
rlm@8 39
rlm@8 40 endmodule
rlm@8 41