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https://github.com/openhwgroup/cvw
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58 lines
2.6 KiB
Systemverilog
58 lines
2.6 KiB
Systemverilog
///////////////////////////////////////////
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// privmode.sv
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//
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// Written: David_Harris@hmc.edu 12 May 2022
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// Modified:
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//
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// Purpose: Track privilege mode. Change on traps and returns.
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//
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// Documentation: RISC-V System on Chip Design Chapter 5
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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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module privmode import cvw::*; #(parameter cvw_t P) (
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input logic clk, reset,
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input logic StallW,
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input logic TrapM, // Trap
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input logic mretM, sretM, // return instruction
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input logic DelegateM, // trap delegated to supervisor mode
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input logic [1:0] STATUS_MPP, // machine trap previous privilege mode
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input logic STATUS_SPP, // supervisor trap previous privilege mode
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output logic [1:0] NextPrivilegeModeM, // next privilege mode, used when updating STATUS CSR on a trap
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output logic [1:0] PrivilegeModeW // current privilege mode
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);
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if (P.U_SUPPORTED) begin:privmode
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// PrivilegeMode FSM
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always_comb begin
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if (TrapM) begin // Change privilege based on DELEG registers (see 3.1.8)
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if (P.S_SUPPORTED & DelegateM) NextPrivilegeModeM = P.S_MODE;
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else NextPrivilegeModeM = P.M_MODE;
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end else if (mretM) NextPrivilegeModeM = STATUS_MPP;
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else if (sretM) NextPrivilegeModeM = {1'b0, STATUS_SPP};
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else NextPrivilegeModeM = PrivilegeModeW;
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end
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flopenl #(2) privmodereg(clk, reset, ~StallW, NextPrivilegeModeM, P.M_MODE, PrivilegeModeW);
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end else begin // only machine mode supported
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assign NextPrivilegeModeM = P.M_MODE;
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assign PrivilegeModeW = P.M_MODE;
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end
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endmodule
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