forked from Github_Repos/cvw
110 lines
3.8 KiB
Systemverilog
110 lines
3.8 KiB
Systemverilog
///////////////////////////////////////////
|
|
// gshare.sv
|
|
//
|
|
// Written: Shreya Sanghai
|
|
// Email: ssanghai@hmc.edu
|
|
// Created: March 16, 2021
|
|
// Modified:
|
|
//
|
|
// Purpose: Gshare predictor with parameterized global history register
|
|
//
|
|
// A component of the Wally configurable RISC-V project.
|
|
//
|
|
// Copyright (C) 2021 Harvey Mudd College & Oklahoma State University
|
|
//
|
|
// Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation
|
|
// files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy,
|
|
// modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software
|
|
// is furnished to do so, subject to the following conditions:
|
|
//
|
|
// The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
|
|
//
|
|
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
|
|
// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
|
|
// BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT
|
|
// OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
|
|
///////////////////////////////////////////
|
|
|
|
`include "wally-config.vh"
|
|
|
|
module gsharePredictor
|
|
#(parameter int k = 10
|
|
)
|
|
(input logic clk,
|
|
input logic reset,
|
|
input logic StallF, StallD, StallE, FlushF, FlushD, FlushE,
|
|
input logic [`XLEN-1:0] LookUpPC,
|
|
output logic [1:0] Prediction,
|
|
// update
|
|
input logic [`XLEN-1:0] UpdatePC,
|
|
input logic UpdateEN, PCSrcE,
|
|
input logic [1:0] UpdatePrediction
|
|
|
|
);
|
|
|
|
logic [k-1:0] GHRF, GHRD, GHRE;
|
|
logic [k-1:0] LookUpPCIndexD, LookUpPCIndexE;
|
|
logic [k-1:0] LookUpPCIndex, UpdatePCIndex;
|
|
logic [1:0] PredictionMemory;
|
|
logic DoForwarding, DoForwardingF;
|
|
logic [1:0] UpdatePredictionF;
|
|
|
|
flopenr #(k) GlobalHistoryRegister(.clk(clk),
|
|
.reset(reset),
|
|
.en(UpdateEN),
|
|
.d({PCSrcE, GHRF[k-1:1] }),
|
|
.q(GHRF));
|
|
|
|
|
|
// for gshare xor the PC with the GHR
|
|
assign UpdatePCIndex = GHRE ^ UpdatePC[k:1];
|
|
assign LookUpPCIndex = GHRF ^ LookUpPC[k:1];
|
|
// Make Prediction by reading the correct address in the PHT and also update the new address in the PHT
|
|
// GHR referes to the address that the past k branches points to in the prediction stage
|
|
// GHRE refers to the address that the past k branches points to in the exectution stage
|
|
SRAM2P1R1W #(k, 2) PHT(.clk(clk),
|
|
.reset(reset),
|
|
.RA1(LookUpPCIndex),
|
|
.RD1(PredictionMemory),
|
|
.REN1(1'b1),
|
|
.WA1(UpdatePCIndex),
|
|
.WD1(UpdatePrediction),
|
|
.WEN1(UpdateEN),
|
|
.BitWEN1(2'b11));
|
|
|
|
|
|
// need to forward when updating to the same address as reading.
|
|
// first we compare to see if the update and lookup addreses are the same
|
|
assign DoForwarding = LookUpPCIndex == UpdatePCIndex;
|
|
|
|
// register the update value and the forwarding signal into the Fetch stage
|
|
// TODO: add stall logic ***
|
|
flopr #(1) DoForwardingReg(.clk(clk),
|
|
.reset(reset),
|
|
.d(DoForwarding),
|
|
.q(DoForwardingF));
|
|
|
|
flopr #(2) UpdatePredictionReg(.clk(clk),
|
|
.reset(reset),
|
|
.d(UpdatePrediction),
|
|
.q(UpdatePredictionF));
|
|
|
|
assign Prediction = DoForwardingF ? UpdatePredictionF : PredictionMemory;
|
|
|
|
//pipeline for GHR
|
|
flopenrc #(k) LookUpDReg(.clk(clk),
|
|
.reset(reset),
|
|
.en(~StallD),
|
|
.clear(FlushD),
|
|
.d(LookUpPCIndex),
|
|
.q(LookUpPCIndexD));
|
|
|
|
flopenrc #(k) LookUpEReg(.clk(clk),
|
|
.reset(reset),
|
|
.en(~StallE),
|
|
.clear(FlushE),
|
|
.d(LookUpPCIndexD),
|
|
.q(LookUpPCIndexE));
|
|
|
|
endmodule
|