pico-python/ws2811.py

from machine import Pin
from rp2 import PIO, StateMachine, asm_pio
from time import sleep_ms, sleep_us
from random import randint

LEDS = 5
PIN = Pin(16)
DELAY = 5

"""
inspired by https://github.com/raspberrypi/pico-micropython-examples/blob/master/pio/pio_ws2812.py
I made this for no other purpose than learning
took me a few hours to understand pio, but if I did it you can too

ws2811 has different timing:
0 - 250ns, then 1000ns
1 - 600ns, then 650ns
rpi cpu cycle = 8ns

to make things easier, we can split timing:
0 -> 250ns high + 350 low  + 650 low
1 -> 250ns high + 350 high + 650 low

p1 -> 250ns = 31.25 cycles
p2 -> 350ns = 43.75 cycles
p3 -> 650ns = 81.25 cycles
decimal, but it's fine if it's off by some, so we can round
"""

@asm_pio(sideset_init=PIO.OUT_LOW,
         out_shiftdir=PIO.SHIFT_LEFT,
         autopull=True, pull_thresh=24)
def prog():
    label("loop")
    
    # 3rd part
    nop().side(0).delay(14) # 15
    nop().side(0).delay(14) # 30
    nop().side(0).delay(14) # 45 
    nop().side(0).delay(14) # 60
    nop().side(0).delay(14) # 75
    out(x, 1).side(0).delay(5) # 81. get one bit of color
    
    # 1st part
    nop().side(1).delay(15) # 16
    jmp(not_x, "zero").side(1).delay(14) # 31. check if zero
    
    # 2nd part for 1 bit
    nop().side(1).delay(14) # 15
    nop().side(1).delay(14) # 30
    jmp("loop").side(1).delay(12) # 43
    
    # 2nd part for 0 bit
    label("zero")
    nop().side(0).delay(14) # 15
    nop().side(0).delay(14) # 30
    nop().side(0).delay(12) # 43

sm = StateMachine(0, prog, sideset_base=PIN)
sm.active(1)

def transition_step(src_hex: int, tgt_hex: int, prog: float):
    src_hex += int(( (tgt_hex >> 16) - (src_hex >> 16) ) * prog) << 16
    src_hex += int(( (tgt_hex >> 8 & 0xFF) - (src_hex >> 8 & 0xFF) ) * prog) << 8
    src_hex += int(( (tgt_hex & 0xFF) - (src_hex & 0xFF) ) * prog)
    
    return src_hex

cols = [randint(0, 0xFFFFFF) for i in range(LEDS)]
cols_new = cols[1:] + [randint(0, 0xFFFFFF)]

while True:
    cols.pop(0)
    cols.append(cols_new[-1])
    cols_new.pop(0)
    cols_new.append(randint(0, 0xFFFFFF))
    
    for i in range(0, 100):
        for l in range(LEDS):
            cold = transition_step(cols[l], cols_new[l], i / 100)
            sm.put(cold, 8) # I don't know why 8 not 24
        sleep_ms(DELAY)