///////////////////////////////////////////
// mmu.sv
//
// Written: david_harris@hmc.edu and kmacsaigoren@hmc.edu 4 June 2021
// Modified: 
//
// Purpose: Memory management unit, including TLB, PMA, PMP
// 
// 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 mmu #(parameter TLB_ENTRIES = 8, // number of TLB Entries
             parameter IMMU = 0) (

  input logic              clk, reset,
  // Current value of satp CSR (from privileged unit)
  input logic  [`XLEN-1:0] SATP_REGW,
  input logic              STATUS_MXR, STATUS_SUM, STATUS_MPRV,
  input logic  [1:0]       STATUS_MPP,

  // Current privilege level of the processeor
  input logic  [1:0]       PrivilegeModeW,

  // 00 - TLB is not being accessed
  // 1x - TLB is accessed for a read (or an instruction)
  // x1 - TLB is accessed for a write
  // 11 - TLB is accessed for both read and write
  input logic              DisableTranslation,

  // VAdr goes to the TLB only. Virtual if the TLB is active.
  // PAdr goes to address mux bypassing the TLB.  PAdr used when there is no translation.
  // Comes from either the program address (instruction address or load/store address)
  // or from the hardware pagetable walker.
  // PAdr is intended to used as a phsycial address.  Discarded by the address mux when translation is
  // performed.  
  // PhysicalAddress is selected to be PAdr when no translation or the translated VAdr (TLBPAdr)
  // when there is translation.
  input logic  [`PA_BITS-1:0] PAdr,  // *** consider renaming this.
  input logic  [`XLEN-1:0] VAdr,
  input logic  [1:0]       Size, // 00 = 8 bits, 01 = 16 bits, 10 = 32 bits , 11 = 64 bits

  // Controls for writing a new entry to the TLB
  input logic  [`XLEN-1:0] PTE,
  input logic  [1:0]       PageTypeWriteVal,
  input logic              TLBWrite,

  // Invalidate all TLB entries
  input logic              TLBFlush,

  // Physical address outputs
  output logic [`PA_BITS-1:0] PhysicalAddress,
  output logic             TLBMiss,
  output logic             TLBHit,
  output logic             Cacheable, Idempotent, AtomicAllowed,

  // Faults
  output logic             TLBPageFault,
  output logic             InstrAccessFaultF, LoadAccessFaultM, StoreAccessFaultM,

  // PMA checker signals
  input  logic             AtomicAccessM, ExecuteAccessF, WriteAccessM, ReadAccessM,
  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], 

  output logic             SquashBusAccess // *** send to privileged unit
//  output logic [5:0]       SelRegions

);

  logic [`PA_BITS-1:0] TLBPAdr;
  logic PMPSquashBusAccess, PMASquashBusAccess;
  // Translation lookaside buffer

  logic PMAInstrAccessFaultF, PMPInstrAccessFaultF;
  logic PMALoadAccessFaultM, PMPLoadAccessFaultM;
  logic PMAStoreAccessFaultM, PMPStoreAccessFaultM;
  logic Translate;


  // only instantiate TLB if Virtual Memory is supported
  generate
    if (`MEM_VIRTMEM) begin
      logic ReadAccess, WriteAccess;
      assign ReadAccess = ExecuteAccessF | ReadAccessM; // execute also acts as a TLB read.  Execute and Read are never active for the same MMU, so safe to mix pipestages
      assign WriteAccess = WriteAccessM;
      tlb #(.TLB_ENTRIES(TLB_ENTRIES), .ITLB(IMMU)) 
        tlb(.SATP_MODE(SATP_REGW[`XLEN-1:`XLEN-`SVMODE_BITS]),
            .SATP_ASID(SATP_REGW[`ASID_BASE+`ASID_BITS-1:`ASID_BASE]),
	    .VAdr,
	    .*);

    end else begin // just pass address through as physical
      assign Translate = 0;
      assign TLBMiss = 0;
      assign TLBHit = 1; // *** is this necessary
      assign TLBPageFault = 0;
     end
  endgenerate

  // If translation is occuring, select translated physical address from TLB
  mux2 #(`PA_BITS) addressmux(PAdr, TLBPAdr, Translate, PhysicalAddress);
  
  ///////////////////////////////////////////
  // Check physical memory accesses
  ///////////////////////////////////////////

  pmachecker pmachecker(.*);
  pmpchecker pmpchecker(.*);


  // If TLB miss and translating we want to not have faults from the PMA and PMP checkers.
  assign SquashBusAccess = PMASquashBusAccess | PMPSquashBusAccess;
  assign InstrAccessFaultF = (PMAInstrAccessFaultF | PMPInstrAccessFaultF) & ~(Translate & ~TLBHit);
  assign LoadAccessFaultM = (PMALoadAccessFaultM | PMPLoadAccessFaultM) & ~(Translate & ~TLBHit);
  assign StoreAccessFaultM = (PMAStoreAccessFaultM | PMPStoreAccessFaultM) & ~(Translate & ~TLBHit);  

endmodule