Projects~PIO~pico.txt
  see fadeLed.pio
      sigGen.pio

  also see Article 164, 193

Source 01: https://ephotocaption.com/a/186/MagPi119.pdf
            pp54 by Ben Everard July 2022

Source 02: Article S166:03 PicoMite (MMBASIC)

who writes

Fortunately, RP2040 has a little trick up its sleeve:
Programmed input/output (PIO). This lets you attach
a state machine (basically a very simple processor)
to some I/O pins and do some simple processing.
Crucially for us, they have very accurate timings.
We've looked at PIO a few times before, so we
won't cover it in detail, but the program we load into
the state machine is:

@asm_pio(out_init=(PIO.OUT_LOW, PIO.OUT_LOW,PIO.
OUT_LOW,PIO.OUT_LOW,PIO.OUT_LOW,PIO.OUT_LOW,PIO.
OUT_LOW,), out_shiftdir=PIO.SHIFT_RIGHT
def seven_bit_dac():

 label("loop")
 pull()
 out(pins, 7) [2]
 out(pins, 7) [2]
 out(pins, 7) [2]
 out(pins, 7)
 jmp("loop")

etc

/Projects~PIO~pico.txt