/* Wishbone_driver.v - Implements a classic wishbone master

   This file is part of the 9086 project.

   Copyright (c) 2024 Efthymios Kritikos

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

module Wishbone_IO_driver (
	input wire clock,
	input wire reset_n,

	input wire [2:0] address,
	input wire [15:0] data_bus_in,
	output reg [15:0] data_bus_out,
	input read_n,
	input write_n,
	input chip_select_n,

	input  wire          wb_ctrl_ack,
	output wire   [29:0] wb_ctrl_adr,
	output wire    [1:0] wb_ctrl_bte,
	output wire    [2:0] wb_ctrl_cti,
	output wire          wb_ctrl_cyc,
	input  wire   [31:0] wb_ctrl_dat_r,
	output wire   [31:0] wb_ctrl_dat_w,
	input  wire          wb_ctrl_err,
	output wire    [3:0] wb_ctrl_sel,
	output wire          wb_ctrl_stb,
	output wire          wb_ctrl_we
);

reg [13:0]WISHBONE_ADDR=14'd0;
reg WISHBONE_ACTIVE_CYCLE=1'b0;
wire WISHBONE_ERROR_IN;
reg [3:0]WISHBONE_SELECT=4'd0;
reg WISHBONE_VALID_TRANSFER=1'b0;
reg WISHBONE_WRITE=1'b1;
wire WISHBONE_ACK_IN;
reg [31:0]WISHBONE_DATA_READ=32'd0;
wire [31:0]WISHBONE_DATA_WRITE;

assign WISHBONE_ACK_IN=wb_ctrl_ack;
assign wb_ctrl_adr={16'd0,WISHBONE_ADDR};
assign WISHBONE_ERROR_IN=wb_ctrl_err;
assign wb_ctrl_sel=WISHBONE_SELECT;
assign wb_ctrl_stb=WISHBONE_VALID_TRANSFER;
assign wb_ctrl_cyc=WISHBONE_ACTIVE_CYCLE;
assign wb_ctrl_we=WISHBONE_WRITE;
assign wb_ctrl_bte=2'b00; // Burst Type Extension   00:Linear burst
assign wb_ctrl_cti=3'b000; // Cycle Type Idenfier   000:Classic cycle
assign WISHBONE_DATA_WRITE=wb_ctrl_dat_r;
assign wb_ctrl_dat_w=WISHBONE_DATA_READ;

reg [31:0]WISHBONE_READ_BUFFER;

reg [1:0]just_transacted;

reg [1:0]WISHBONE_STATUS;

wire CYCLE_END=(WISHBONE_ACK_IN==1'b1);//||WISHBONE_ERROR_IN==1'b1);

always @( posedge clock )begin
	if(reset_n==0)begin
		just_transacted<=2'b0;
	end
	if(just_transacted==2'd1&&CYCLE_END==1'b1)begin
		WISHBONE_READ_BUFFER<=WISHBONE_DATA_WRITE;
	end
	if(chip_select_n==0 && write_n==0 )begin
		case (address)
			3'h0: WISHBONE_DATA_READ[15:0] <=data_bus_in;
			3'h1: WISHBONE_DATA_READ[31:16]<=data_bus_in;
			3'h2: WISHBONE_ADDR[13:0]<=data_bus_in[13:0];
			3'h3: begin end
			default: begin end
		endcase

		case (address)
			3'h3: begin
				WISHBONE_ACTIVE_CYCLE<=1;
				WISHBONE_VALID_TRANSFER<=1;
				WISHBONE_SELECT<=4'hF;
			end
			default: begin end
		endcase
		if(address==3'h3)begin
			WISHBONE_WRITE<=1'b1;//data_bus_in[0:0];
			if(data_bus_in[0:0]==1'b1)begin //write req
				just_transacted<=2'd2;
			end else begin
				just_transacted<=2'd1;
			end
		end
	end else if(just_transacted!=2'd0&&CYCLE_END==1'b1)begin // In the unlikely scenario that the CPU wants to write without having checked for the previous write
		WISHBONE_STATUS[0:0]<=WISHBONE_ACK_IN;
		WISHBONE_STATUS[1:1]<=WISHBONE_ERROR_IN;
		WISHBONE_ACTIVE_CYCLE<=0;
		WISHBONE_VALID_TRANSFER<=0;
		just_transacted<=2'b0;
	end

	if ( chip_select_n==0 && read_n==0 )begin
		case (address)
			/* verilator lint_off BLKSEQ */
			/* Makes icarus verilog work as expected, not too sure if it helps real hardware yet*/
			3'h0: data_bus_out = WISHBONE_READ_BUFFER[15:0];
			3'h1: data_bus_out = WISHBONE_READ_BUFFER[31:16];
			3'h2: data_bus_out = {13'd0,WISHBONE_STATUS,just_transacted==2'd0||CYCLE_END==1'b1}; //1:NOT BUSY   0:BUSY
			default: data_bus_out = 16'h0;
			/* verilator lint_on BLKSEQ */
		endcase
	end
end

endmodule