doom_riscv/cores/e1/rtl/e1_rx_liu.v

/*
 * e1_rx_liu.v
 *
 * vim: ts=4 sw=4
 *
 * E1 RX interface to external LIU
 *
 *
 * Copyright (C) 2019  Sylvain Munaut <tnt@246tNt.com>
 * All rights reserved.
 *
 * LGPL v3+, see LICENSE.lgpl3
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */

`default_nettype none

module e1_rx_liu (
	// Pads
	input  wire pad_rx_data,
	input  wire pad_rx_clk,

	// Output
	output reg  out_data,
	output reg  out_valid,

	// Common
	input  wire clk,
	input  wire rst
);

	wire rx_data;
	wire rx_clk;

	reg  rx_data_r;
	reg  rx_clk_r;

	// IOBs (registered)
	SB_IO #(
		.PIN_TYPE(6'b0000_00),
		.PULLUP(1'b0),
		.NEG_TRIGGER(1'b0)
	) rx_iobs_I[1:0] (
		.PACKAGE_PIN({pad_rx_data, pad_rx_clk}),
		.LATCH_INPUT_VALUE(1'b0),
		.CLOCK_ENABLE(1'b1),
		.INPUT_CLK(clk),
		.OUTPUT_CLK(1'b0),
		.OUTPUT_ENABLE(1'b0),
		.D_OUT_0(1'b0),
		.D_OUT_1(1'b0),
		.D_IN_0({rx_data, rx_clk}),
		.D_IN_1()
	);

	// First internal register
	always @(posedge clk)
	begin
		rx_data_r <= rx_data;
		rx_clk_r  <= rx_clk;
	end

	// Second internal register + clk falling edge detect
	always @(posedge clk)
	begin
		out_data  <= rx_data_r;
		out_valid <= rx_clk_r & ~rx_clk;
	end

endmodule // e1_rx_liu