///////////////////////////////////////////
// tlb_ram.sv
//
// Written: jtorrey@hmc.edu & tfleming@hmc.edu 16 February 2021
// Modified:
//
// Purpose: Stores page table entries of cached address translations.
//          Outputs the physical page number and access bits of the current
//          virtual address on a TLB hit.
// 
// 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 tlb_ram #(parameter ENTRY_BITS = 3) (
  input                   clk, reset,
  input  [ENTRY_BITS-1:0] VPNIndex,  // Index to read from
  input  [ENTRY_BITS-1:0] WriteIndex,
  input  [`XLEN-1:0]      PageTableEntryWrite,
  input                   TLBWrite,

  output [`PPN_BITS-1:0]  PhysicalPageNumber,
  output [7:0]            PTEAccessBits
);

  localparam NENTRIES = 2**ENTRY_BITS;

  logic [`XLEN-1:0] ram [0:NENTRIES-1];
  logic [`XLEN-1:0] PageTableEntry;

  logic [NENTRIES-1:0] RAMEntryWrite;

  decoder #(ENTRY_BITS) tlb_ram_decoder(WriteIndex, RAMEntryWrite);

  // Generate a flop for every entry in the RAM
  generate
    genvar i;
    for (i = 0; i < NENTRIES; i++) begin: tlb_ram_flops
      flopenr #(`XLEN) pte_flop(clk, reset, RAMEntryWrite[i] & TLBWrite,
        PageTableEntryWrite, ram[i]);
    end
  endgenerate

  assign PageTableEntry = ram[VPNIndex];
  assign PTEAccessBits = PageTableEntry[7:0];
  assign PhysicalPageNumber = PageTableEntry[`PPN_BITS+9:10];

endmodule