Add LED example

Add a small LED example to let me test the blinker functionality.

Signed-off-by: Sean Anderson <seanga2@gmail.com>

examples/README.adoc

@@ -6,3 +6,4 @@ cores in this project.
 :leveloffset: +1
 
 include::breakout_hub/README.adoc[]
+include::led/README.adoc[]

examples/led/README.adoc

@@ -0,0 +1,11 @@
+= LED Blinker test
+
+This directory contains an example design to test the LED blinkers. It runs on an
+https://www.olimex.com/Products/FPGA/iCE40/iCE40HX8K-EVB/[Olimex iCE40HX8K-EVB].
+Pushing the buttons will cause the LEDs to blink at 30 Hz.
+
+To compile this design, run
+
+    $ make examples/led/top.bin
+
+from the root directory of this repository.

examples/led/top.pcf

@@ -0,0 +1,5 @@
+set_io -nowarn clk_100 J3
+set_io -nowarn LED[0] M12
+set_io -nowarn LED[1] R16
+set_io -nowarn BUT[0] K11
+set_io -nowarn BUT[1] P13

examples/led/top.v

@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: AGPL-3.0-Only
+/*
+ * Copyright (C) 2022 Sean Anderson <seanga2@gmail.com>
+ */
+
+`include "common.vh"
+
+module top (
+	input SYSCLK,
+
+	input [1:0] BUT,
+	output [1:0] LED
+);
+
+	parameter WISHBONE	= 1;
+
+	wire clk_125;
+
+	SB_PLL40_CORE #(
+		.FEEDBACK_PATH("SIMPLE"),
+		.DIVR(4'd0),
+		.DIVF(7'd9),
+		.DIVQ(3'd3),
+		.FILTER_RANGE(3'd5),
+	) pll (
+		.REFERENCECLK(SYSCLK),
+		.PLLOUTGLOBAL(clk_125),
+		.BYPASS(1'b0),
+		.RESETB(1'b1)
+	);
+
+	wire [1:0] led_n;
+	assign LED = ~led_n;
+
+	led_blinker #(
+		.LEDS(2)
+	) blinker(
+		.clk(clk_125),
+		.triggers(~BUT),
+		.out(led_n),
+		.test_mode(1'b0)
+	);
+
+endmodule