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87 lines
2.6 KiB
Systemverilog
87 lines
2.6 KiB
Systemverilog
///////////////////////////////////////////
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// RASPredictor.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 15, 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 RASPredictor
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#(parameter int StackSize = 16
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)
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(input logic clk,
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input logic reset,
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input logic PopF,
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output logic [`XLEN-1:0] RASPCF,
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input logic [3:0] WrongPredInstrClassD,
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input logic [3:0] InstrClassD,
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input logic PushE,
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input logic incr,
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input logic [`XLEN-1:0] PCLinkE
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);
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// *** need to update so it either doesn't push until the memory stage
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// or need to repair flushed push.
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// *** need to repair popped and then flushed returns.
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logic CounterEn;
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localparam Depth = $clog2(StackSize);
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logic [Depth-1:0] PtrD, PtrQ, PtrP1, PtrM1;
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logic [StackSize-1:0] [`XLEN-1:0] memory;
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integer index;
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assign CounterEn = PopF | PushE | incr | WrongPredInstrClassD[2];
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assign PtrD = PopF | InstrClassD[2] ? PtrM1 : PtrP1;
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assign PtrM1 = PtrQ - 1'b1;
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assign PtrP1 = PtrQ + 1'b1;
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// may have to handle a PushE and an incr at the same time.
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// *** what happens if jal is executing and there is a return being flushed in Decode?
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flopenr #(Depth) PTR(.clk(clk),
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.reset(reset),
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.en(CounterEn),
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.d(PtrD),
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.q(PtrQ));
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// RAS must be reset.
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always_ff @ (posedge clk) begin
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if(reset) begin
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for(index=0; index<StackSize; index++)
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memory[index] <= {`XLEN{1'b0}};
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end else if(PushE) begin
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memory[PtrP1] <= #1 PCLinkE;
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end
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end
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assign RASPCF = memory[PtrQ];
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endmodule
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