/*
 *       mdio_cont.v
 *
 *	 Copyright (C) 2018, 2019 Mind Chasers Inc.
 *
 *   Licensed under the Apache License, Version 2.0 (the "License");
 *   you may not use this file except in compliance with the License.
 *   You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *   Unless required by applicable law or agreed to in writing, software
 *   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.
 *
 *	function: MDIO controller / state machine
 *
 */

`timescale 1ns /10ps

module mdio_controller		#(parameter ADDR_SZ = 6)
(
	
	// system interface
	input rstn,
	input clk,				// mdio mdc clock	
	
	// worker interface
	input work_start,
	output reg work_run,
	output reg work_done,
	input [ADDR_SZ-1:0] routine_addr,
	
	// arbitration
	input buffer_full,

	// memory interface
	output reg [ADDR_SZ-1:0] addr,	// controller address
	input [7:0] di,			// controller data bus
	
	// mdio interface
	output reg [4:0] reg_addr,
	output reg [15:0] dout,	// data output ( for writes )
	output ld, 				// load control / address, 
	output reg rwn,			// read / write not
	input done
);
	
	localparam ST_SZ = 4;
	reg [ST_SZ-1:0] cont_state;
	wire ld_dl, ld_dh;
	
	
	// state encoding
	localparam 	S0= 4'h0, S1=4'h1, S2=4'h2, S3=4'h3,
				S4= 4'h4, S5=4'h5, S6=4'h6, S7=4'h7,
				S8 = 4'h8;


	/* 
	*  keep running until an eop is found 
	*/
    always @(posedge clk or negedge rstn) 
		begin 
			if (!rstn)
				cont_state <= S0;
			else
				case (cont_state)
					S0: if (work_start == 1'b1) cont_state <= S1;
					S1: cont_state <= S2;
					S2: if ( work_done == 1'b1 ) cont_state <= S0;
						else if ( buffer_full ) cont_state <= S2;	// wait for the fifo to empty out
						else if ( ~rwn ) cont_state <= S3;
						else cont_state <= S6;
					S3: cont_state <= S4;
					S4: cont_state <= S5;
					S5: cont_state <= S6;
					S6: cont_state <= S7;
					S7: if ( done == 1'b1 ) cont_state <= S8;
					S8: cont_state <= S1;
				endcase
		end
	
	/* read the eop bit during S1 */
	always @(posedge clk or negedge rstn)
		begin
			if ( !rstn )
				work_done <= 1'b0;
			else if ( cont_state == S1 && di[7] == 1'b1 ) 
				work_done <= 1'b1;
			else
				work_done <= 1'b0;
		end
		
	/* work_run */
	always @(posedge clk or negedge rstn)
		begin
			if ( !rstn )
				work_run <= 1'b0;
			else if ( work_start == 1'b1 ) 
				work_run <= 1'b1;
			else if ( work_done == 1'b1 )
				work_run <= 1'b0;
		end	
		
	/* set RWN for duration of cyle */
	always @(posedge clk or negedge rstn)
		begin
			if ( rstn == 1'b0 || work_done ==1'b1 )
				begin
					rwn <= 1'b1;
				end
			else if ( cont_state == S1 )
				begin
					rwn <= di[5];
				end		
		end
				
	/* reg_addr is the mdio register address */
	always @(posedge clk or negedge rstn)
		begin
			if ( rstn == 1'b0 || work_done ==1'b1 )
				reg_addr <= 5'h0;
			else if ( cont_state == S1 )
				reg_addr <= di[4:0];	  
		end
		
	/* addr is the program address */
	always @(posedge clk or negedge rstn)
		begin
			if (rstn == 1'b0 || work_done == 1'b1 )
				addr <= 0;
			else if ( work_start == 1'b1 )
				addr <= routine_addr[ADDR_SZ-1:0];
			else if ( cont_state == S3 || cont_state == S4 || cont_state == S8 )
				addr <= addr + 1;
		end
				
	// latch the write data to mdio
	always @(posedge clk or negedge rstn)
		begin
			if (rstn == 0)
				dout <= 16'h0000;
			else if ( ld_dl == 1'b1 )
				dout[7:0] <= di;
			else if ( ld_dh == 1'b1 )
				dout[15:8] <= di;
		end
		
	// combinatorial logic here
	assign ld_dl = ( cont_state == S4 ) ? 1'b1 : 1'b0;
	assign ld_dh = ( cont_state == S5 ) ? 1'b1 : 1'b0;
	assign ld = ( cont_state == S6 ) ? 1'b1 : 1'b0;
	

endmodule