Struct BlinkyExample

pub struct BlinkyExample;

Blinky!

The definitive example in FPGA firmware land is a simple LED blinker. This typically involves a clock that is fed to the FPGA with a pre-defined frequency, and an output signal that can control an LED. Because we don’t know what FPGA we are using, we will do this in simulation first. We want a blink that is 250 msec long every second, and our clock speed is (a comically slow) 10kHz. Here is a minimal working Blinky! example:

use std::time::Duration;
use rust_hdl::core::prelude::*;
use rust_hdl::docs::vcd2svg::vcd_to_svg;
use rust_hdl::widgets::prelude::*;

const CLOCK_SPEED_HZ : u64 = 10_000;


#[derive(LogicBlock)]
struct Blinky {
    pub clock: Signal<In, Clock>,
    pulser: Pulser,
    pub led: Signal<Out, Bit>,
}

impl Default for Blinky {
   fn default() -> Self {
       Self {
         clock: Default::default(),
         pulser: Pulser::new(CLOCK_SPEED_HZ, 1.0, Duration::from_millis(250)),
         led: Default::default(),
       }
    }
}

impl Logic for Blinky {
    #[hdl_gen]
    fn update(&mut self) {
       self.pulser.clock.next = self.clock.val();
       self.pulser.enable.next = true.into();
       self.led.next = self.pulser.pulse.val();
    }
}

let mut sim = simple_sim!(Blinky, clock, CLOCK_SPEED_HZ, ep, {
    let mut x = ep.init()?;
    wait_clock_cycles!(ep, clock, x, 4*CLOCK_SPEED_HZ);
    ep.done(x)
});

let mut uut = Blinky::default();
uut.connect_all();
sim.run_to_file(Box::new(uut), 5*SIMULATION_TIME_ONE_SECOND, "/tmp/blinky.vcd").unwrap();
vcd_to_svg("/tmp/blinky.vcd","images/blinky_all.svg",&["uut.clock", "uut.led"], 0, 4_000_000_000_000).unwrap();
vcd_to_svg("/tmp/blinky.vcd","images/blinky_pulse.svg",&["uut.clock", "uut.led"], 900_000_000_000, 1_500_000_000_000).unwrap();

Running the above (a release run is highly recommended) will generate a vcd file (which is a trace file for FPGAs and hardware in general). You can open this using e.g., gtkwave. Here you will see (with some manipulation of the UI)

And a zoom in shows the 250 msec pulse.