///////////////////////////////////////////
// lsuArb.sv
//
// Written: Ross THompson and Kip Macsai-Goren
// Modified: kmacsaigoren@hmc.edu June 23, 2021
//
// Purpose: LSU arbiter between the CPU's demand request for data memory and
//          the page table walker
// 
// 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 lsuArb 
  (input  logic clk, reset,

   // from page table walker
   input logic 		    SelPTW,
   input logic 		    HPTWRead,
   input logic [`XLEN-1:0]  HPTWPAdrE,
   output logic 	    HPTWStall, 

   // from CPU
   input logic [1:0] 	    MemRWM,
   input logic [2:0] 	    Funct3M,
   input logic [1:0] 	    AtomicM,
   input logic [`XLEN-1:0]  MemAdrM,
   input logic [`XLEN-1:0]  MemAdrE,
   input logic 		    StallW,
   input logic 		    PendingInterruptM,
   // to CPU
   output logic [`XLEN-1:0] ReadDataW,
   output logic 	    SquashSCW,
   output logic 	    DataMisalignedM,
   output logic 	    CommittedM,
   output logic 	    LSUStall, 
  
   // to D Cache
   output logic 	    DisableTranslation, 
   output logic [1:0] 	    MemRWMtoDCache,
   output logic [2:0] 	    Funct3MtoDCache,
   output logic [1:0] 	    AtomicMtoDCache,
   output logic [`XLEN-1:0] MemAdrMtoDCache,
   output logic [`XLEN-1:0] MemAdrEtoDCache, 
   output logic 	    StallWtoDCache,
   output logic 	    PendingInterruptMtoDCache,
   

   // from D Cache
   input logic 		    CommittedMfromDCache,
   input logic 		    SquashSCWfromDCache,
   input logic 		    DataMisalignedMfromDCache,
   input logic [`XLEN-1:0]  ReadDataWfromDCache,
   input logic 		    DCacheStall
  
   );

  logic [2:0] PTWSize;
  logic [`XLEN-1:0]  HPTWPAdrM;
  
  // multiplex the outputs to LSU
  assign DisableTranslation = SelPTW;  // change names between SelPTW would be confusing in DTLB.
  assign MemRWMtoDCache = SelPTW ? {HPTWRead, 1'b0} : MemRWM;
  
  generate
    assign PTWSize = (`XLEN==32 ? 3'b010 : 3'b011); // 32 or 64-bit access from htpw
  endgenerate
  mux2 #(3) sizemux(Funct3M, PTWSize, SelPTW, Funct3MtoDCache);

  flop #(`XLEN) HPTWPAdrMReg(clk, HPTWPAdrE, HPTWPAdrM);   // delay HPTWPAdr by a cycle

  assign AtomicMtoDCache = SelPTW ? 2'b00 : AtomicM;
  assign MemAdrMtoDCache = SelPTW ? HPTWPAdrM : MemAdrM;
  assign MemAdrEtoDCache = SelPTW ? HPTWPAdrE : MemAdrE;  
  assign StallWtoDCache = SelPTW ? 1'b0 : StallW;
  // always block interrupts when using the hardware page table walker.
  assign CommittedM = SelPTW ? 1'b1 : CommittedMfromDCache;

  // demux the inputs from LSU to walker or cpu's data port.

  assign ReadDataW = SelPTW ? `XLEN'b0 : ReadDataWfromDCache;  // probably can avoid this demux
  assign SquashSCW = SelPTW ? 1'b0 : SquashSCWfromDCache;
  assign DataMisalignedM = SelPTW ? 1'b0 : DataMisalignedMfromDCache;
  // *** need to rename DcacheStall and Datastall.
  // not clear at all.  I think it should be LSUStall from the LSU,
  // which is demuxed to HPTWStall and CPUDataStall? (not sure on this last one).
  assign HPTWStall = SelPTW ? DCacheStall : 1'b1;  

  assign PendingInterruptMtoDCache = SelPTW ? 1'b0 : PendingInterruptM;

  assign LSUStall = SelPTW ? 1'b1 : DCacheStall; // *** this is probably going to change.
  
endmodule