new-sonar/gateware/sampler/peak_detector.py

from migen import *

class PeakDetector(Module):
    """
    Module to detect when peak to peak voltage is high enough to consider incoming
    data to be a valid ping. Configuration is provided by setting the configuration
    attributes. Do not change these settings while detector is running.

    Attributes
    ----------
    data: (input)
        Data signal to use for detection

    data_valid: (input)
        Strobed signal that indicates value on `data` is valid to be read

    enable: (input)
        Enables running peak detection. De-asserting this will clear all state variables

    triggered: (output)
        Signal that indicates peak has been triggered. Only cleared once enable is de-asserted again

    Configuration Attributes
    ------------------------
    thresh_value:
        Minimum peak to peak value considered triggered

    thresh_time:
        Number of consecutive samples above threshold required to consider triggered

    decay_value:
        Decay value to subtract from peak values to prevent false triggers

    decay_period:
        Number of samples between each application of decay
    """

    def __init__(self, data_width: int):
        # Create all state signals
        min_val = Signal(data_width)
        max_val = Signal(data_width)
        diff = Signal(data_width)
        triggered_time = Signal(32)
        decay_counter = Signal(32)

        # Control signals
        self.data = Signal(data_width)
        self.data_valid = Signal()
        self.enable = Signal()
        self.triggered = Signal()

        # Configuration Parameters
        self.thresh_value = Signal(data_width)
        self.thresh_time = Signal(32)
        self.decay_value = Signal(data_width)
        self.decay_period = Signal(32)

        self.sync += If(~self.enable,
            # Reset halfway. ADCs are 0-2V, and everything should be centered at 1V, so this is approximating the initial value
            min_val.eq(int(2**data_width /2)),
            max_val.eq(int(2**data_width /2)),
            self.triggered.eq(0),
            decay_counter.eq(0),
            triggered_time.eq(0),
        )

        # Constantly updating diff to simplify some statements
        self.comb += diff.eq(max_val - min_val)

        self.sync += If(self.enable & self.data_valid,
            # Update maximum value
            If(self.data > max_val, max_val.eq(self.data)),
            # Update minimum value
            If(self.data < min_val, min_val.eq(self.data)),
            If(diff > self.thresh_value,
               # We have met the threshold for triggering, start counting
               triggered_time.eq(triggered_time + 1),
               decay_counter.eq(0),

               # We have triggered, so we can set the output. After this point,
               # nothing we do matters until enable is de-asserted and we reset
               # triggered.
               If(triggered_time + 1 >= self.thresh_time, self.triggered.eq(1)))
            .Else(
                # We have not met the threshold, reset timer and handle decay
                triggered_time.eq(0),
                decay_counter.eq(decay_counter + 1),

                # Decay threshold has been reached, apply decay to peaks
                If(decay_counter >= self.decay_period,
                   decay_counter.eq(0),

                   # Only apply decay if the values would not overlap, and we use the decay
                   If((diff >= (self.decay_value << 1)) & (self.decay_value > 0),
                      max_val.eq(max_val - self.decay_value),
                      min_val.eq(min_val + self.decay_value)))
            )
        )


from typing import Tuple
import numpy as np
import matplotlib.pyplot as plt


def create_waveform(dc_bias: int = 0, scale: float = 1) -> Tuple[np.ndarray[float], np.ndarray[int]]:
    """
    Create a simple 40kHz sine wave in integer values that can be used by peak detector
    """
    assert scale <= 1.0, "Scale factor must be some ratio of full range"

    # Constants
    f_s = 10e6              # Sample rate (Hz)
    f = 40e3                # Signal Frequency (Hz)
    t = 0.002               # Sample period (s)
    n = int(f_s * 0.002)    # Number of samples

    # Create time from 0ms to 2ms
    x = np.linspace(0, t, n)

    # Create signal!
    y = np.sin(x * 2*np.pi*f)

    # Scale according to user inputs
    y = y * scale

    # Convert to positive integer at provided bias
    signal = np.ndarray((len(y)), dtype=np.uint16)
    # "unsafe" casting because numpy doesn't know we are staying under 10 bit values
    np.copyto(signal, y * 512 + 512 + dc_bias, casting='unsafe')

    #plt.plot(x, signal)
    #plt.show()

    return x, signal


def set_settings(dut: PeakDetector, thresh_value: int, thresh_time: int, decay_value: int, decay_period: int) -> None:
    """Set peak detector settings simply"""
    (yield dut.thresh_value.eq(thresh_value))
    (yield dut.thresh_time.eq(thresh_time))
    (yield dut.decay_value.eq(decay_value))
    (yield dut.decay_period.eq(decay_period))

    # Load in values with a new clock
    yield


def test_simple_waveform():
    (_, signal) = create_waveform()
    dut = PeakDetector(10)

    def test_fn():
        # First set settings to be simple, we want to trigger pretty much immediately
        yield from set_settings(dut, 800, 10, 0, 0)

        # Enable device
        (yield dut.enable.eq(1))
        yield

        # Load data in until we trigger
        for i, val in enumerate(signal):
            if (yield dut.triggered) == 1:
                # Test passed!
                return

            # Load in data, set valid
            (yield dut.data.eq(int(val)))
            (yield dut.data_valid.eq(1))
            yield # Tick

        assert False, "No trigger, test has failed..."

    run_simulation(dut, test_fn(), vcd_name="peak_detector.vcd")