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//
// TV80 8-Bit Microprocessor Core
// Based on the VHDL T80 core by Daniel Wallner (jesus@opencores.org)
//
// Copyright (c) 2004 Guy Hutchison (ghutchis@opencores.org)
//
// 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.
 
// Negative-edge based wrapper allows memory wait_n signal to work
// correctly without resorting to asynchronous logic.
 
module tv80n (/*AUTOARG*/
  // Outputs
  m1_n, mreq_n, iorq_n, rd_n, wr_n, rfsh_n, halt_n, busak_n, A, do, 
  // Inputs
  reset_n, clk, wait_n, int_n, nmi_n, busrq_n, di
  );
 
  parameter Mode = 0;    // 0 => Z80, 1 => Fast Z80, 2 => 8080, 3 => GB
  parameter T2Write = 0; // 0 => wr_n active in T3, /=0 => wr_n active in T2
  parameter IOWait  = 1; // 0 => Single cycle I/O, 1 => Std I/O cycle
 
 
  input         reset_n; 
  input         clk; 
  input         wait_n; 
  input         int_n; 
  input         nmi_n; 
  input         busrq_n; 
  output        m1_n; 
  output        mreq_n; 
  output        iorq_n; 
  output        rd_n; 
  output        wr_n; 
  output        rfsh_n; 
  output        halt_n; 
  output        busak_n; 
  output [15:0] A;
  input [7:0]   di;
  output [7:0]  do;
 
  reg           mreq_n; 
  reg           iorq_n; 
  reg           rd_n; 
  reg           wr_n; 
  reg           nxt_mreq_n; 
  reg           nxt_iorq_n; 
  reg           nxt_rd_n; 
  reg           nxt_wr_n; 
 
  wire          cen;
  wire          intcycle_n;
  wire          no_read;
  wire          write;
  wire          iorq;
  reg [7:0]     di_reg;
  wire [6:0]    mcycle;
  wire [6:0]    tstate;
 
  assign    cen = 1;
 
  tv80_core #(Mode, IOWait) i_tv80_core
    (
     .cen (cen),
     .m1_n (m1_n),
     .iorq (iorq),
     .no_read (no_read),
     .write (write),
     .rfsh_n (rfsh_n),
     .halt_n (halt_n),
     .wait_n (wait_n),
     .int_n (int_n),
     .nmi_n (nmi_n),
     .reset_n (reset_n),
     .busrq_n (busrq_n),
     .busak_n (busak_n),
     .clk (clk),
     .IntE (),
     .stop (),
     .A (A),
     .dinst (di),
     .di (di_reg),
     .do (do),
     .mc (mcycle),
     .ts (tstate),
     .intcycle_n (intcycle_n)
     );  
 
  always @*
    begin
      nxt_mreq_n = 1;
      nxt_rd_n   = 1;
      nxt_iorq_n = 1;
      nxt_wr_n   = 1;
 
      if (mcycle[0])
        begin
	  if (tstate[1] || tstate[2])
            begin
	      nxt_rd_n = ~ intcycle_n;
	      nxt_mreq_n = ~ intcycle_n;
	      nxt_iorq_n = intcycle_n;
	    end
        end // if (mcycle[0])          
      else
        begin
	  if ((tstate[1] || tstate[2]) && !no_read && !write)
            begin
	      nxt_rd_n = 1'b0;
	      nxt_iorq_n = ~ iorq;
	      nxt_mreq_n = iorq;
	    end
	  if (T2Write == 0)
            begin                          
	      if (tstate[2] && write)
                begin
		  nxt_wr_n = 1'b0;
		  nxt_iorq_n = ~ iorq;
		  nxt_mreq_n = iorq;
                end
            end
	  else
            begin
	      if ((tstate[1] || (tstate[2] && !wait_n)) && write)
                begin
		  nxt_wr_n = 1'b0;
		  nxt_iorq_n = ~ iorq;
		  nxt_mreq_n = iorq;
		end
	    end // else: !if(T2write == 0)          
	end // else: !if(mcycle[0])
    end // always @ *
 
  always @(negedge clk)
    begin
      if (!reset_n)
        begin
	  rd_n   <= #1 1'b1;
	  wr_n   <= #1 1'b1;
	  iorq_n <= #1 1'b1;
	  mreq_n <= #1 1'b1;
        end
      else
        begin
	  rd_n <= #1 nxt_rd_n;
	  wr_n <= #1 nxt_wr_n;
	  iorq_n <= #1 nxt_iorq_n;
	  mreq_n <= #1 nxt_mreq_n;
	end // else: !if(!reset_n)
    end // always @ (posedge clk or negedge reset_n)
 
  always @(posedge clk)
    begin
      if (!reset_n)
        begin
	  di_reg <= #1 0;
        end
      else
        begin
	  if (tstate[2] && wait_n == 1'b1)
	    di_reg <= #1 di;
	end // else: !if(!reset_n)
    end // always @ (posedge clk)
 
endmodule // t80n