Mercurial > pygar

     1 import RegFile::*;

     2 import ProcTypes::*;

     3 import FIFO::*;

     4 

     5 typedef Maybe#(Addr) BrPred;

     6 typedef Bit#(4) BPindx;

     7 

     8 typedef struct {Addr brpc; Addr nextpc;} BrPair deriving (Bits,Eq);

     9 

    10 typedef union tagged

    11 {

    12   BrPair Valid;

    13   void Invalid;

    14 } CBranchPath deriving(Bits, Eq);	// have the cache start out invalid and add valid values.

    15 

    16 interface BranchPred;

    17    method BrPred get(Addr pres);  //returns a maybe type that is invalid if no predition

    18    method Action upd(Addr pres, Addr next);

    19 endinterface

    20 

    21 module mkBranchPred(BranchPred);

    22 

    23    //state variables

    24    RegFile#(BPindx, CBranchPath)  bcache <- mkRegFileFull(); // cache to hold 16 (based on BPindx)

    25 

    26    method Action upd(Addr pres, Addr next);

    27       BrPair brp;

    28       brp = BrPair {brpc:pres, nextpc:next};

    29       bcache.upd(pres[5:2], tagged Valid brp);

    30    endmethod

    31 

    32    method BrPred get(Addr prespc);

    33       BPindx rd = prespc[5:2];

    34       let cbp = bcache.sub(rd);

    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

    36 	 return tagged Valid bp.nextpc;

    37       else return Invalid;

    38    endmethod

    39    

    40 endmodule

    41
author	punk
date	Tue, 13 Apr 2010 17:34:33 -0400
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