///////////////////////////////////////////
// ahbinterface.sv
//
// Written: Ross Thompson ross1728@gmail.com August 29, 2022
// Modified: 
//
// Purpose: Cache/Bus data path.
// Bus Side logic
// register the fetch data from the next level of memory.
// This register should be necessary for timing.  There is no register in the uncore or
// ahblite controller between the memories and this cache.
// 
// A component of the 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 ahbinterface #(parameter LSU = 0) // **** modify to use LSU/ifu parameter to control widths of buses
  (
  input logic                HCLK, HRESETn,
  
  // bus interface
  input logic                HREADY,
  input logic [`XLEN-1:0]    HRDATA,
  output logic [1:0]         HTRANS,
  output logic               HWRITE,
  output logic [`XLEN-1:0]   HWDATA,
  output logic [`XLEN/8-1:0] HWSTRB,
  
  // lsu/ifu interface
  input logic                Flush,
  input logic [1:0]          BusRW,
  input logic [`XLEN/8-1:0]  ByteMask,
  input logic [`XLEN-1:0]    WriteData,
  input logic                Stall,
  output logic               BusStall,
  output logic               BusCommitted,
  output logic [(LSU ? `XLEN : 32)-1:0]   FetchBuffer);
  
  logic                       CaptureEn;

  /// *** only 32 bit for IFU.
  localparam                  LEN = (LSU ? `XLEN : 32);
  
  flopen #(LEN) fb(.clk(HCLK), .en(CaptureEn), .d(HRDATA[LEN-1:0]), .q(FetchBuffer));

  if(LSU) begin
    // delay HWDATA by 1 cycle per spec; *** assumes AHBW = XLEN    
    flop #(`XLEN) wdreg(HCLK, WriteData, HWDATA); 
    flop #(`XLEN/8) HWSTRBReg(HCLK, ByteMask, HWSTRB);
  end else begin
    assign HWDATA = '0;
    assign HWSTRB = '0;
  end    

  busfsm busfsm(.HCLK, .HRESETn, .Flush, .BusRW,
    .BusCommitted, .Stall, .BusStall, .CaptureEn, .HREADY,
    .HTRANS, .HWRITE);
endmodule