Retune neopixel timings on SAMD51. They were too slow.

[tannewt]

Test the timings a reference PWM output because CPU clock isn't perfect.

import neopixel_write
import digitalio
import time
import board
import pulseio

pwm = pulseio.PWMOut(board.D10)
pwm.duty_cycle = 2 ** 15

pin = digitalio.DigitalInOut(board.D12)
pin.direction=digitalio.Direction.OUTPUT
pixel_off=bytearray([0,0,0,0])
pixel_on=bytearray([0,255,0,0])
while True:
    neopixel_write.neopixel_write(pin,pixel_off)
    time.sleep(1)
    neopixel_write.neopixel_write(pin,pixel_on)
    time.sleep(1)

Fixes #1083

[dhalbert]

Great!

[dhalbert]

Will wait for @jerryneedell to test, if he has time.

[jerryneedell]

@dhalbert Sorry, I may not be able to test it for a week or so.

[jerryneedell]

I downloaded and tested https://adafruit-circuit-python.s3.amazonaws.com/index.html?prefix=bin/itsybitsy_m4_express/ commit 2e80f37
-- it works as before when conencted to 3V power and a 3V GPIO pin (D13) but it still fails is powered via VUSB and the 5V D5 pin?

can you verify that I used the correct build?
it shows up as

Adafruit CircuitPython 3.0.0-4-g2e80f37 on 2018-08-08; Adafruit ItsyBitsy M4 Express with samd51g19