LED blink without CPU

A project log for Arduino Compatible Zynq Shield

Xilinx Zynq SoC, Arduino Compatible, 2x ARM Cortex A9, LPDDR2 Memory, USB OTG, on-board USB JTAG and UART.

Antti LukatsAntti Lukats 02/04/2016 at 18:390 Comments

For simple LED blink, we can use internal clock and forget totally that there is a hard processor available. This design work equally well on any Artix, Kintex, Virtex or Zynq board!

If we want to write the Blinky in VHDL, then this is equally easy:

We send the clock to output port, and create wrapper that is not managed, then we can just write normal VHDL. Of course we could just instantiate the startup directly in VHDL too.

library IEEE;


library UNISIM;


entity blink_top_wrapper is

  port (

    LED : out std_logic


end blink_top_wrapper;

architecture STRUCTURE of blink_top_wrapper is

  component blink_top is

  port (

    clk66mhz : out STD_LOGIC


  end component blink_top;

signal clk: std_logic;  


blink_top_i: component blink_top

     port map (

      clk66mhz => clk -- this is free running clock from BD


    -- LED is steady on!

    LED <= '1';


This is basically the vivado generated wrapper, 3 lines changed.

This design takes the clock from PS PLL, from FCLK0. This design only works if Zynq CPU has executed the FSBL (first stage bootloader). Again we can use this clock from the PS PLL in our plain VHDL code.