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//======================================================================
//
// eim_indicator.v
// ---------------
// A simple LED indicator to show that the EIM is alive.
//
//
// Author: Pavel Shatov
// Copyright (c) 2014, NORDUnet A/S All rights reserved.
//
// 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 NORDUnet 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 THE COPYRIGHT
// HOLDER OR CONTRIBUTORS 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.
//
//======================================================================

module eim_indicator
	(
		sys_clk, sys_rst,
		eim_active,
		led_out
    );

		//
		// Ports
		//
	input		wire	sys_clk;
	input		wire	sys_rst;
	input		wire	eim_active;
	output	wire	led_out;

		//
		// Parameters
		//
	localparam	CNT_BITS		= 24;	// led will be dim for 2**(24-1) = 8388608 ticks, which is ~100 ms @ 80 MHz.

		//
		// Counter
		//
	reg	[CNT_BITS-1:0]		cnt;

	always @(posedge sys_clk)
		//
		if (sys_rst)								cnt	<= {CNT_BITS{1'b0}};
		else if (cnt > {CNT_BITS{1'b0}})		cnt	<= cnt - 1'b1;
		else if (eim_active)						cnt	<= {CNT_BITS{1'b1}};

	assign led_out = ~cnt[CNT_BITS-1];

endmodule

//======================================================================
// EOF eim_indicator.v
//======================================================================