cvw/pipelined/src/privileged/privdec.sv
2023-01-11 15:15:08 -08:00

93 lines
4.5 KiB
Systemverilog

///////////////////////////////////////////
// privdec.sv
//
// Written: David_Harris@hmc.edu 9 January 2021
// Modified:
//
// Purpose: Decode Privileged & related instructions
// See RISC-V Privileged Mode Specification 20190608 3.1.10-11
//
// A component of the CORE-V-WALLY configurable RISC-V project.
//
// Copyright (C) 2021-23 Harvey Mudd College & Oklahoma State University
//
// SPDX-License-Identifier: Apache-2.0 WITH SHL-2.1
//
// Licensed under the Solderpad Hardware License v 2.1 (the “License”); you may not use this file
// except in compliance with the License, or, at your option, the Apache License version 2.0. You
// may obtain a copy of the License at
//
// https://solderpad.org/licenses/SHL-2.1/
//
// Unless required by applicable law or agreed to in writing, any work distributed under the
// License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
// either express or implied. See the License for the specific language governing permissions
// and limitations under the License.
////////////////////////////////////////////////////////////////////////////////////////////////
`include "wally-config.vh"
module privdec (
input logic clk, reset,
input logic StallM,
input logic [31:20] InstrM,
input logic PrivilegedM, IllegalIEUInstrFaultM, IllegalCSRAccessM, IllegalFPUInstrM,
input logic [1:0] PrivilegeModeW,
input logic STATUS_TSR, STATUS_TVM, STATUS_TW,
output logic IllegalInstrFaultM,
output logic EcallFaultM, BreakpointFaultM,
output logic sretM, mretM, wfiM, sfencevmaM);
logic IllegalPrivilegedInstrM;
logic WFITimeoutM;
logic StallMQ;
logic ebreakM, ecallM;
///////////////////////////////////////////
// Decode privileged instructions
///////////////////////////////////////////
assign sretM = PrivilegedM & (InstrM[31:20] == 12'b000100000010) & `S_SUPPORTED &
(PrivilegeModeW == `M_MODE | PrivilegeModeW == `S_MODE & ~STATUS_TSR);
assign mretM = PrivilegedM & (InstrM[31:20] == 12'b001100000010) & (PrivilegeModeW == `M_MODE);
assign ecallM = PrivilegedM & (InstrM[31:20] == 12'b000000000000);
assign ebreakM = PrivilegedM & (InstrM[31:20] == 12'b000000000001);
assign wfiM = PrivilegedM & (InstrM[31:20] == 12'b000100000101);
assign sfencevmaM = PrivilegedM & (InstrM[31:25] == 7'b0001001) &
(PrivilegeModeW == `M_MODE | (PrivilegeModeW == `S_MODE & ~STATUS_TVM));
///////////////////////////////////////////
// WFI timeout Privileged Spec 3.1.6.5
///////////////////////////////////////////
if (`U_SUPPORTED) begin:wfi
logic [`WFI_TIMEOUT_BIT:0] WFICount, WFICountPlus1;
assign WFICountPlus1 = WFICount + 1;
floprc #(`WFI_TIMEOUT_BIT+1) wficountreg(clk, reset, ~wfiM, WFICountPlus1, WFICount); // count while in WFI
assign WFITimeoutM = ((STATUS_TW & PrivilegeModeW != `M_MODE) | (`S_SUPPORTED & PrivilegeModeW == `U_MODE)) & WFICount[`WFI_TIMEOUT_BIT];
end else assign WFITimeoutM = 0;
///////////////////////////////////////////
// Extract exceptions by name and handle them
///////////////////////////////////////////
assign BreakpointFaultM = ebreakM; // could have other causes from a debugger
assign EcallFaultM = ecallM;
///////////////////////////////////////////
// sfence.vma causes TLB flushes
///////////////////////////////////////////
// sets ITLBFlush to pulse for one cycle of the sfence.vma instruction
// In this instr we want to flush the tlb and then do a pagetable walk to update the itlb and continue the program.
// But we're still in the stalled sfence instruction, so if itlbflushf == sfencevmaM, tlbflush would never drop and
// the tlbwrite would never take place after the pagetable walk. by adding in ~StallMQ, we are able to drop itlbflush
// after a cycle AND pulse it for another cycle on any further back-to-back sfences.
// flopr #(1) StallMReg(.clk, .reset, .d(StallM), .q(StallMQ));
// assign ITLBFlushF = sfencevmaM & ~StallMQ;
// assign DTLBFlushM = sfencevmaM;
///////////////////////////////////////////
// Fault on illegal instructions
///////////////////////////////////////////
assign IllegalPrivilegedInstrM = PrivilegedM & ~(sretM|mretM|ecallM|ebreakM|wfiM|sfencevmaM);
assign IllegalInstrFaultM = (IllegalIEUInstrFaultM & IllegalFPUInstrM) | IllegalPrivilegedInstrM | IllegalCSRAccessM |
WFITimeoutM;
endmodule