icestick_ring_oscillator.v

`timescale 1ns / 1ps
// iCEstick signals
//
// clk_12MHz: on board 12MHz crystal oscillator
//
// USB <-> RS232 converter has standard RS232 signals
// DCD, DSR, DTR, CTS, RTS, RXD, TXD
//
//              /----------------------------------------
//             /    A7 A6 A5 A4 A3 A2 A1 A0  GND  +3.3V |
//            /                                         |
//  ---------/                                          |
//  |                    LED0           C0 C4           |
//  |                                   C1 C5           |
//  |              LED3  LED4  LED1     C2 C6           |
//  |                                   C3 C7           |
//  |                    LED2          GND GND          |
//  ---------\                        3.3V 3.3V         |
//            \                                         |
//             \    B7 B6 B5 B4 B3 B2 B1 B0  GND  +3.3V |
//              \----------------------------------------
//

module top (
	output A0
);                    

	
// ring oscillator

	parameter taps = 3;
	wire [taps:0] buffers_in, buffers_out;
	assign buffers_in = {buffers_out[taps-1:0], chain_in};
	assign chain_out = buffers_out[taps];
	assign chain_in = !chain_out;

	SB_LUT4 #(
		.LUT_INIT(16'd2)
	) buffers [taps:0] (
		.O(buffers_out),
		.I0(buffers_in),
		.I1(1'b0),
		.I2(1'b0),
		.I3(1'b0)
	);

	assign A0 = chain_out;
endmodule