MicroPython IR remote dimmer on a Pico: keys 0 to 3

# Dim an LED from the remote: keys 0 to 3 set four brightness levels for
# the LED on GP14 (PWM), and each key beeps the buzzer behind GP15.
from machine import Pin, PWM
import time
from ir_nec import NEC, code

remote = NEC(16)
led = PWM(Pin(14))
led.freq(10000)
led.duty_u16(0)
buzzer = Pin(15, Pin.OUT, value=0)

LEVELS = {0xFF6897: ("0", 0), 0xFF30CF: ("1", 6000), 0xFF18E7: ("2", 20000), 0xFF7A85: ("3", 65535)}

while True:
    frame = remote.read()
    if frame is None or frame == "repeat":
        continue
    key = LEVELS.get(code(frame))
    if key:
        name, duty = key
        buzzer.value(1)
        led.duty_u16(duty)
        print("key", name, "brightness", duty * 100 // 65535, "%")
        time.sleep_ms(100)
        buzzer.value(0)

# ir_nec.py: read an NEC infrared remote from a receiver's output.
# The receiver pulls its output low while it sees the remote's 38 kHz light.
# A frame is a 9 ms low leader, a 4.5 ms gap, then 32 bits, each a 0.56 ms
# low followed by a short (0) or long (1) high. A held button repeats with a
# 2.25 ms gap and no bits.
from machine import Pin, time_pulse_us

class NEC:
    def __init__(self, pin):
        self.pin = Pin(pin, Pin.IN, Pin.PULL_UP)

    def read(self, wait_us=200000):
        """A frame's 32 bits (first bit lowest), 'repeat', or None."""
        if time_pulse_us(self.pin, 0, wait_us) < 8000:
            return None
        gap = time_pulse_us(self.pin, 1, 6000)
        if gap < 0:
            return None
        if gap < 3000:
            return "repeat"
        bits = 0
        for i in range(32):
            if time_pulse_us(self.pin, 0, 2000) < 0:
                return None
            high = time_pulse_us(self.pin, 1, 3000)
            if high < 0:
                return None
            if high > 1000:
                bits |= 1 << i
        return bits

def reverse8(b):
    out = 0
    for _ in range(8):
        out = (out << 1) | (b & 1)
        b >>= 1
    return out

def code(bits):
    """A frame as the familiar 0xFF.... code: the bits read in arrival order."""
    command = (bits >> 16) & 0xFF
    return 0xFF0000 | (reverse8(command) << 8) | reverse8(command ^ 0xFF)