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https://github.com/openhwgroup/cvw
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78 lines
3.0 KiB
Systemverilog
78 lines
3.0 KiB
Systemverilog
///////////////////////////////////////////
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// twoBitPredictor.sv
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//
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// Written: Ross Thomposn
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// Email: ross1728@gmail.com
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// Created: February 14, 2021
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// Modified:
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//
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// Purpose: 2 bit saturating counter predictor with parameterized table depth.
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//
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// A component of the CORE-V-WALLY configurable RISC-V project.
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//
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// Copyright (C) 2021-23 Harvey Mudd College & Oklahoma State University
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//
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// SPDX-License-Identifier: Apache-2.0 WITH SHL-2.1
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//
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// Licensed under the Solderpad Hardware License v 2.1 (the “License”); you may not use this file
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// except in compliance with the License, or, at your option, the Apache License version 2.0. You
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// may obtain a copy of the License at
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//
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// https://solderpad.org/licenses/SHL-2.1/
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//
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// Unless required by applicable law or agreed to in writing, any work distributed under the
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// License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
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// either express or implied. See the License for the specific language governing permissions
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// and limitations under the License.
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////////////////////////////////////////////////////////////////////////////////////////////////
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`include "wally-config.vh"
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module twoBitPredictor
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#(parameter int k = 10
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)
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(input logic clk,
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input logic reset,
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input logic StallF, StallD, StallE, StallM,
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input logic FlushD, FlushE, FlushM,
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input logic [`XLEN-1:0] PCNextF, PCM,
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output logic [1:0] DirPredictionF,
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output logic DirPredictionWrongE,
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input logic BranchInstrE, BranchInstrM,
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input logic PCSrcE
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);
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logic [k-1:0] IndexNextF, IndexM;
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logic [1:0] PredictionMemory;
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logic DoForwarding, DoForwardingF;
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logic [1:0] DirPredictionD, DirPredictionE;
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logic [1:0] NewDirPredictionE, NewDirPredictionM;
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// hashing function for indexing the PC
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// We have k bits to index, but XLEN bits as the input.
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// bit 0 is always 0, bit 1 is 0 if using 4 byte instructions, but is not always 0 if
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// using compressed instructions. XOR bit 1 with the MSB of index.
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assign IndexNextF = {PCNextF[k+1] ^ PCNextF[1], PCNextF[k:2]};
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assign IndexM = {PCM[k+1] ^ PCM[1], PCM[k:2]};
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ram2p1r1wbe #(2**k, 2) PHT(.clk(clk),
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.ce1(~StallF), .ce2(~StallM & ~FlushM),
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.ra1(IndexNextF),
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.rd1(DirPredictionF),
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.wa2(IndexM),
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.wd2(NewDirPredictionM),
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.we2(BranchInstrM & ~StallM & ~FlushM),
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.bwe2(1'b1));
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flopenrc #(2) PredictionRegD(clk, reset, FlushD, ~StallD, DirPredictionF, DirPredictionD);
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flopenrc #(2) PredictionRegE(clk, reset, FlushE, ~StallE, DirPredictionD, DirPredictionE);
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assign DirPredictionWrongE = PCSrcE != DirPredictionE[1] & BranchInstrE;
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satCounter2 BPDirUpdateE(.BrDir(PCSrcE), .OldState(DirPredictionE), .NewState(NewDirPredictionE));
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flopenrc #(2) NewPredictionRegM(clk, reset, FlushM, ~StallM, NewDirPredictionE, NewDirPredictionM);
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endmodule
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