/*
 * nano_dsi_data.v
 *
 * vim: ts=4 sw=4
 *
 * Copyright (C) 2019  Sylvain Munaut <tnt@246tNt.com>
 * All rights reserved.
 *
 * BSD 3-clause, see LICENSE.bsd
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the <organization> nor the
 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

`default_nettype none

module nano_dsi_data (
	// nano-PMOD - DATA lane
	output wire data_lp,
	output wire data_hs_p,
	output wire data_hs_n,

	// Control/Packet interface
	input  wire hs_start,
	input  wire [7:0] hs_data,
	input  wire hs_last,
	output wire hs_ack,
	output wire hs_rdy,

	// Clock/Data sync
	input  wire clk_sync,

	// Config
	input  wire [7:0] cfg_hs_prep,
	input  wire [7:0] cfg_hs_zero,
	input  wire [7:0] cfg_hs_trail,

	// Clock / Reset
	input  wire clk,
	input  wire rst
);

	// Signals
	// -------

	// IO control
	reg io_lp;

	reg io_hs_active;
	reg io_hs_bit;

	// FSM
	localparam
		ST_LP11				= 0,
		ST_LP00				= 1,
		ST_HS_ZERO			= 2,
		ST_HS_SYNC			= 3,
		ST_HS_DATA			= 4,
		ST_HS_TRAIL			= 5;

	reg  [2:0] fsm_state;
	reg  [2:0] fsm_state_next;

	// Timer
	reg  [7:0] timer_val;
	wire timer_trig;

	// Shift register
	reg  [7:0] shift_reg;
	reg  [3:0] shift_cnt;
	reg  shift_last;

	reg  hs_bit_final;


	// IOBs
	// ----

	// LP drivers
	SB_IO #(
		.PIN_TYPE(6'b100100),
		.PULLUP(1'b0),
		.NEG_TRIGGER(1'b0),
		.IO_STANDARD("SB_LVCMOS")
	) iob_data_lp_I (
		.PACKAGE_PIN(data_lp),
		.CLOCK_ENABLE(1'b1),
//		.INPUT_CLK(1'b0),
		.OUTPUT_CLK(clk),
		.OUTPUT_ENABLE(1'b1),
		.D_OUT_0(io_lp),
		.D_OUT_1(1'b0),
		.D_IN_0(),
		.D_IN_1()
	);

	// HS drivers
	SB_IO #(
		.PIN_TYPE(6'b100100),
		.PULLUP(1'b0),
		.NEG_TRIGGER(1'b0),
		.IO_STANDARD("SB_LVCMOS")
	) iob_data_hs_p_I (
		.PACKAGE_PIN(data_hs_p),
		.CLOCK_ENABLE(1'b1),
//		.INPUT_CLK(1'b0),
		.OUTPUT_CLK(clk),
		.OUTPUT_ENABLE(io_hs_active),
		.D_OUT_0(io_hs_bit),
		.D_OUT_1(1'b0),
		.D_IN_0(),
		.D_IN_1()
	);

	SB_IO #(
		.PIN_TYPE(6'b100100),
		.PULLUP(1'b0),
		.NEG_TRIGGER(1'b0),
		.IO_STANDARD("SB_LVCMOS")
	) iob_data_hs_n_I (
		.PACKAGE_PIN(data_hs_n),
		.CLOCK_ENABLE(1'b1),
//		.INPUT_CLK(1'b0),
		.OUTPUT_CLK(clk),
		.OUTPUT_ENABLE(io_hs_active),
		.D_OUT_0(~io_hs_bit),
		.D_OUT_1(1'b0),
		.D_IN_0(),
		.D_IN_1()
	);


	// FSM
	// ---

	// State register
	always @(posedge clk or posedge rst)
		if (rst)
			fsm_state <= ST_LP11;
		else
			fsm_state <= fsm_state_next;

	// Next State logic
	always @(*)
	begin
		// Default is to not move
		fsm_state_next = fsm_state;

		// Transitions ?
		case (fsm_state)
			ST_LP11:
				if (hs_start)
					fsm_state_next = ST_LP00;

			ST_LP00:
				if (timer_trig)
					fsm_state_next = ST_HS_ZERO;

			ST_HS_ZERO:
				if (timer_trig)
					fsm_state_next = ST_HS_SYNC;

			ST_HS_SYNC:
				if (clk_sync)
					fsm_state_next = ST_HS_DATA;

			ST_HS_DATA:
				if (shift_cnt[3] && shift_last)
					fsm_state_next = ST_HS_TRAIL;

			ST_HS_TRAIL:
				if (timer_trig)
					fsm_state_next = ST_LP11;
		endcase
	end


	// Timer
	// -----

	always @(posedge clk)
	begin
		if (fsm_state != fsm_state_next) begin
			// Default is to trigger all the time
			timer_val <= 8'h80;

			// Preload for next state
			case (fsm_state_next)
				ST_LP00:			timer_val <= cfg_hs_prep;
				ST_HS_ZERO:			timer_val <= cfg_hs_zero;
				ST_HS_TRAIL:		timer_val <= cfg_hs_trail;
			endcase
		end else begin
			timer_val  <= timer_val - 1;
		end
	end

	assign timer_trig = timer_val[7];


	// Shift register
	// --------------

	always @(posedge clk)
		if (fsm_state == ST_HS_SYNC) begin
			shift_reg  <= 8'hB8;						// SoT
			shift_last <= 1'b0;
		end else if (fsm_state == ST_HS_DATA) begin
			if (shift_cnt[3]) begin
				shift_reg  <= hs_data;					// Load
				shift_last <= hs_last;
			end else begin
				shift_reg  <= { 1'b0, shift_reg[7:1] };	// Shift LSB out
				shift_last <= shift_last;
			end
		end

	always @(posedge clk)
		if ((fsm_state != ST_HS_DATA) || shift_cnt[3])
			shift_cnt <= 4'h1;
		else
			shift_cnt <= shift_cnt + 1;

	assign hs_ack = shift_cnt[3];
	assign hs_rdy = (fsm_state == ST_LP11);

	always @(posedge clk)
		if (shift_cnt[3] & shift_last)
			hs_bit_final <= ~shift_reg[0];


	// IO control
	// ----------

	always @(posedge clk)
	begin
		io_lp <= (fsm_state == ST_LP11);

		io_hs_active <=
			(fsm_state == ST_HS_ZERO) ||
			(fsm_state == ST_HS_SYNC) ||
			(fsm_state == ST_HS_DATA) ||
			(fsm_state == ST_HS_TRAIL);

		if (fsm_state == ST_HS_DATA)
			io_hs_bit <= shift_reg[0];
		else if (fsm_state == ST_HS_TRAIL)
			io_hs_bit <= hs_bit_final;
		else
			io_hs_bit <= 1'b0;
	end

endmodule // nano_dsi_data