/*
 *  PicoSoC - A simple example SoC using PicoRV32
 *
 *  Copyright (C) 2017  Clifford Wolf <clifford@clifford.at>
 *
 *  Permission to use, copy, modify, and/or distribute this software for any
 *  purpose with or without fee is hereby granted, provided that the above
 *  copyright notice and this permission notice appear in all copies.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 */

module spimemio (
	input clk, resetn,

	input valid,
	output ready,
	input [23:0] addr,
	output reg [31:0] rdata,

	output flash_csb,
	output flash_clk,

	output flash_io0_oe,
	output flash_io1_oe,
	output flash_io2_oe,
	output flash_io3_oe,

	output flash_io0_do,
	output flash_io1_do,
	output flash_io2_do,
	output flash_io3_do,

	input  flash_io0_di,
	input  flash_io1_di,
	input  flash_io2_di,
	input  flash_io3_di
);
	reg        xfer_resetn;
	reg        din_valid;
	wire       din_ready;
	reg  [7:0] din_data;
	reg        din_cont;
	reg        din_qspi;
	reg        din_ddr;
	reg        din_rd;

	wire       dout_valid;
	wire [7:0] dout_data;

	reg [23:0] buffer;
	reg [3:0] buffer_wen;

	reg [23:0] rd_addr;
	reg rd_valid;
	reg rd_wait;
	reg rd_inc;

	assign ready = valid && (addr == rd_addr) && rd_valid;
	wire jump = valid && !ready && (addr != rd_addr+4) && rd_valid;

	spimemio_xfer xfer (
		.clk          (clk         ),
		.resetn       (xfer_resetn ),
		.din_valid    (din_valid   ),
		.din_ready    (din_ready   ),
		.din_data     (din_data    ),
		.din_cont     (din_cont    ),
		.din_qspi     (din_qspi    ),
		.din_ddr      (din_ddr     ),
		.din_rd       (din_rd      ),
		.dout_valid   (dout_valid  ),
		.dout_data    (dout_data   ),
		.flash_csb    (flash_csb   ),
		.flash_clk    (flash_clk   ),
		.flash_io0_oe (flash_io0_oe),
		.flash_io1_oe (flash_io1_oe),
		.flash_io2_oe (flash_io2_oe),
		.flash_io3_oe (flash_io3_oe),
		.flash_io0_do (flash_io0_do),
		.flash_io1_do (flash_io1_do),
		.flash_io2_do (flash_io2_do),
		.flash_io3_do (flash_io3_do),
		.flash_io0_di (flash_io0_di),
		.flash_io1_di (flash_io1_di),
		.flash_io2_di (flash_io2_di),
		.flash_io3_di (flash_io3_di)
	);

	reg [3:0] state;

	always @(posedge clk) begin
		xfer_resetn <= 1;
		din_valid <= 0;
		din_data <= 8'h 00;

		if (!resetn) begin
			state <= 0;
			xfer_resetn <= 0;
			rd_valid <= 0;
			din_cont <= 0;
			din_qspi <= 0;
			din_ddr <= 0;
			din_rd <= 0;
		end else begin
			if (dout_valid && buffer_wen[0]) buffer[ 7: 0] <= dout_data;
			if (dout_valid && buffer_wen[1]) buffer[15: 8] <= dout_data;
			if (dout_valid && buffer_wen[2]) buffer[23:16] <= dout_data;
			if (dout_valid && buffer_wen[3]) begin
				rdata <= {dout_data, buffer};
				rd_addr <= rd_inc ? rd_addr + 4 : addr;
				rd_valid <= 1;
				rd_wait <= rd_inc;
				rd_inc <= 1;
			end

			if (dout_valid && buffer_wen) begin
				buffer_wen <= 0;
			end

			if (valid)
				rd_wait <= 0;

			case (state)
				0: begin
					din_valid <= 1;
					din_data <= 8'h ff;
					if (din_ready)
						state <= 1;
				end
				1: begin
					if (dout_valid) begin
						xfer_resetn <= 0;
						state <= 2;
					end
				end
				2: begin
					din_valid <= 1;
					din_data <= 8'h ab;
					if (din_ready)
						state <= 3;
				end
				3: begin
					if (dout_valid) begin
						xfer_resetn <= 0;
						state <= 4;
					end
				end
				4: begin
					rd_inc <= 0;
					din_valid <= 1;
					din_data <= 8'h 03;
					if (din_ready)
						state <= 5;
				end
				5: begin
					if (valid && !ready) begin
						din_valid <= 1;
						din_data <= addr[23:16];
						if (din_ready)
							state <= 6;
					end
				end
				6: begin
					din_valid <= 1;
					din_data <= addr[15:8];
					if (din_ready)
						state <= 7;
				end
				7: begin
					din_valid <= 1;
					din_data <= addr[7:0];
					if (din_ready)
						state <= 8;
				end
				8: begin
					din_valid <= 1;
					din_data <= 8'h 00;
					if (din_ready) begin
						buffer_wen <= 4'b 0001;
						state <= 9;
					end
				end
				9: begin
					din_valid <= 1;
					din_data <= 8'h 00;
					if (din_ready) begin
						buffer_wen <= 4'b 0010;
						state <= 10;
					end
				end
				10: begin
					din_valid <= 1;
					din_data <= 8'h 00;
					if (din_ready) begin
						buffer_wen <= 4'b 0100;
						state <= 11;
					end
				end
				11: begin
					if (!rd_wait || valid) begin
						din_valid <= 1;
						din_data <= 8'h 00;
						if (din_ready) begin
							buffer_wen <= 4'b 1000;
							state <= 8;
						end
					end
				end
			endcase

			if (jump) begin
				rd_inc <= 0;
				rd_valid <= 0;
				xfer_resetn <= 0;
				state <= 4;
			end
		end
	end
endmodule

module spimemio_xfer (
	input clk, resetn,

	input            din_valid,
	output           din_ready,
	input      [7:0] din_data,
	input            din_cont,
	input            din_qspi,
	input            din_ddr,
	input            din_rd,

	output           dout_valid,
	output     [7:0] dout_data,

	output reg flash_csb,
	output reg flash_clk,

	output reg flash_io0_oe,
	output reg flash_io1_oe,
	output reg flash_io2_oe,
	output reg flash_io3_oe,

	output reg flash_io0_do,
	output reg flash_io1_do,
	output reg flash_io2_do,
	output reg flash_io3_do,

	input      flash_io0_di,
	input      flash_io1_di,
	input      flash_io2_di,
	input      flash_io3_di
);
	localparam [3:0] mode_spi = 0;
	reg [3:0] mode;

	reg [7:0] obuffer;
	reg [7:0] ibuffer;

	reg [3:0] count;
	reg xfer_cont;
	reg xfer_qspi;
	reg xfer_ddr;
	reg xfer_rd;

	reg [7:0] next_obuffer;
	reg [7:0] next_ibuffer;
	reg [3:0] next_count;

	reg fetch_next;
	reg last_fetch_next;

	assign din_ready = din_valid && resetn && fetch_next;

	assign dout_valid = fetch_next && !last_fetch_next;
	assign dout_data = ibuffer;

	always @* begin
		flash_io0_oe = 0;
		flash_io1_oe = 0;
		flash_io2_oe = 0;
		flash_io3_oe = 0;

		flash_io0_do = 0;
		flash_io1_do = 0;
		flash_io2_do = 0;
		flash_io3_do = 0;

		next_obuffer = obuffer;
		next_ibuffer = ibuffer;
		next_count = count;
		fetch_next = 0;

		case (mode)
			mode_spi: begin
				flash_io0_oe = 1;
				flash_io0_do = obuffer[7];

				if (flash_clk) begin
					next_obuffer = {obuffer[6:0], 1'b 0};
					next_count = count - |count;
				end else begin
					next_ibuffer = {ibuffer[6:0], flash_io1_di};
				end

				fetch_next = (next_count == 0);
			end
		endcase
	end

	always @(posedge clk) begin
		if (!resetn) begin
			mode <= mode_spi;
			last_fetch_next <= 1;
			flash_csb <= 1;
			flash_clk <= 0;
			count <= 0;
		end else begin
			last_fetch_next <= fetch_next;
			if (count) begin
				flash_clk <= !flash_clk && !flash_csb;
				obuffer <= next_obuffer;
				ibuffer <= next_ibuffer;
				count <= next_count;
			end
			if (din_valid && din_ready) begin
				flash_csb <= 0;
				flash_clk <= 0;

				obuffer <= din_data;
				ibuffer <= 8'h 00;
				count <= 8;

				xfer_cont <= din_cont;
				xfer_qspi <= din_qspi;
				xfer_ddr <= din_ddr;
				xfer_rd <= din_rd;
			end
		end
	end
endmodule