cvw/pipelined/src/mmu/pmpchecker.sv

///////////////////////////////////////////
// pmpchecker.sv
//
// Written: tfleming@hmc.edu & jtorrey@hmc.edu 28 April 2021
// Modified: 
//
// Purpose: Examines all physical memory accesses and checks them against the
//          current values of the physical memory protection (PMP) registers.
//          Can raise an access fault on illegal reads, writes, and instruction
//          fetches.
// 
// 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 pmpchecker (
  input  logic [`PA_BITS-1:0]      PhysicalAddress,  
  input  logic [1:0]               PrivilegeModeW,

  // *** ModelSim has a switch -svinputport which controls whether input ports
  // are nets (wires) or vars by default. The default setting of this switch is
  // `relaxed`, which means that signals are nets if and only if they are
  // scalars or one-dimensional vectors. Since this is a two-dimensional vector,
  // this will be understood as a var. However, if we don't supply the `var`
  // keyword, the compiler warns us that it's interpreting the signal as a var,
  // which we might not intend.
  input  var logic [7:0]   PMPCFG_ARRAY_REGW[`PMP_ENTRIES-1:0],
  input  var logic [`XLEN-1:0] PMPADDR_ARRAY_REGW [`PMP_ENTRIES-1:0],
  input  logic             ExecuteAccessF, WriteAccessM, ReadAccessM,
  output logic             PMPInstrAccessFaultF,
  output logic             PMPLoadAccessFaultM,
  output logic             PMPStoreAccessFaultM
);

  if (`PMP_ENTRIES > 0) begin: pmpchecker
    // Bit i is high when the address falls in PMP region i
    logic                    EnforcePMP;
    logic [`PMP_ENTRIES-1:0] Match; // physical address matches one of the pmp ranges
    logic [`PMP_ENTRIES-1:0] FirstMatch; // onehot encoding for the first pmpaddr to match the current address.
    logic [`PMP_ENTRIES-1:0] Active;     // PMP register i is non-null
    logic [`PMP_ENTRIES-1:0] L, X, W, R; // PMP matches and has flag set
    logic [`PMP_ENTRIES-1:0]   PAgePMPAdr;  // for TOR PMP matching, PhysicalAddress > PMPAdr[i]

    pmpadrdec pmpadrdecs[`PMP_ENTRIES-1:0](
      .PhysicalAddress, 
      .PMPCfg(PMPCFG_ARRAY_REGW),
      .PMPAdr(PMPADDR_ARRAY_REGW),
      .PAgePMPAdrIn({PAgePMPAdr[`PMP_ENTRIES-2:0], 1'b1}),
      .PAgePMPAdrOut(PAgePMPAdr),
      .FirstMatch, .Match, .Active, .L, .X, .W, .R);

    priorityonehot #(`PMP_ENTRIES) pmppriority(.a(Match), .y(FirstMatch)); // combine the match signal from all the adress decoders to find the first one that matches.

    // Only enforce PMP checking for S and U modes when at least one PMP is active or in Machine mode when L bit is set in selected region
    assign EnforcePMP = (PrivilegeModeW == `M_MODE) ? |L : |Active; 

    assign PMPInstrAccessFaultF = EnforcePMP & ExecuteAccessF & ~|X;
    assign PMPStoreAccessFaultM = EnforcePMP & WriteAccessM   & ~|W;
    assign PMPLoadAccessFaultM  = EnforcePMP & ReadAccessM    & ~|R;
  end else begin: pmpchecker  // no checker
    assign PMPInstrAccessFaultF = 0;
    assign PMPLoadAccessFaultM = 0;
    assign PMPStoreAccessFaultM = 0;
  end
endmodule