display refresh causes static sounds

[FoamyGuy]

This might ultimately be a displayio/core issue, or some combination of those and audiobusio rather than something specific to this library, but this is where I've noticed first it and created a reproducer.

Refreshing the display seems to cause static if it's done during the while audio.playing loop. This code illustrates the issue:

It uses this bmp: https://github.com/FoamyGuy/Adafruit_CircuitPython_FruitJam_Animation/blob/main/f_spritesheet.bmp
And this wav file: https://cdn-learn.adafruit.com/assets/assets/000/057/463/original/StreetChicken.wav?1531255658

import adafruit_imageload
import adafruit_ticks
import board
from audiocore import WaveFile
import audiobusio
import adafruit_tlv320
import supervisor
from displayio import Group, TileGrid


display = supervisor.runtime.display
display.auto_refresh = False
i2c = board.I2C()
dac = adafruit_tlv320.TLV320DAC3100(i2c)
dac.configure_clocks(sample_rate=22050, bit_depth=16)
dac.headphone_output = True
dac.headphone_volume = -60  # dB
wave_file = open("StreetChicken.wav", "rb")
wave = WaveFile(wave_file)
audio = audiobusio.I2SOut(board.I2S_BCLK, board.I2S_WS, board.I2S_DIN)

main_group = Group()
display.root_group = main_group

bmp, palette = adafruit_imageload.load("f_spritesheet.bmp")

tgs = []
for i in range(5):
    tgs.append(TileGrid(bitmap=bmp, pixel_shader=palette, tile_width=32, tile_height=39))
    tgs[-1].y = 42 * i
    main_group.append(tgs[-1])

index_count = bmp.width // tgs[0].tile_width

interval = 1/30
last_update = adafruit_ticks.ticks_ms() / 1000
cur_x = 0
while True:
    audio.play(wave)

    while audio.playing:
        now = adafruit_ticks.ticks_ms() / 1000
        if last_update + interval < now:
            last_update = now
            cur_x = (cur_x + 1) % 200
            for tg in tgs:
                tg.x = cur_x
                tg[0] = (tg[0] + 1) % index_count
            display.refresh()

    print("Done!")

The amount of static and interference seems correlated to how many pixels on the display need updated. If all of the code making visually changes is commented out the sound plays clearly. If the number of TileGrids is lowered by using something smaller than 5 in for i in range(5): the interference lessens, I don't notice any issues with 1 or 2 TileGrids, I can start to hear some with 3, and by 4 and 5 the interference is very apparent.

Testing performed on:

Adafruit CircuitPython 9.2.5 on 2025-03-19; Adafruit Fruit Jam with rp2350b

With the version of the library from #2 at commit 08a9a85

[BlitzCityDIY]

hihi @FoamyGuy - i'm trying to test this with a max98357a i2s dac but i keep hitting attribute errors for the display. i've tried 9.2.5 and 9.2.6 on both rev a and rev b fruit jams. is there a different build out there?

Traceback (most recent call last):
  File "code.py", line 17, in <module>
AttributeError: can't set attribute 'auto_refresh'

tried commenting out display.auto_refresh = False and then:

Traceback (most recent call last):
  File "code.py", line 24, in <module>
AttributeError: can't set attribute 'root_group'

do you have that dac to see if the same behavior occurs? i'm leaning towards it being an i2s issue since this library only takes care of configuration of the dac and then any audio playback is handled by the core

[BlitzCityDIY]

i was able to use picodvi to init the display:

fb = picodvi.Framebuffer(720, 400, clk_dp=board.CKP, clk_dn=board.CKN,
                                   red_dp=board.D0P, red_dn=board.D0N,
                                   green_dp=board.D1P, green_dn=board.D1N,
                                   blue_dp=board.D2P, blue_dn=board.D2N,
                                   color_depth=8)
display = framebufferio.FramebufferDisplay(fb)

and can recreate the issue with the max i2s DAC too. i notice the difference between setting the TileGrid number from 2 to 5. i tried having the wav file on the sdcard to see if that made a difference but it was the same.

[FoamyGuy]

@BlitzCityDIY Attribute error on the Display stuff I think is when it does not find a display on supervisor.runtime.display as far as I am aware both 9.2.5 and 9.2.6 should automatically initialize that display on the fruit jam. Maybe it requires that the display be plugged in when the board boots up, I'm not sure if I tested booting without a display and then plugging in after.

The other thing that could factor in is the display size. I've noticed that the display I'm using doesn't seem to support the new default display configuration. I've added CIRCUITPY_DISPLAY_WIDTH=320 to my settings.toml file to get the display into a configuration that the display supports.

[BlitzCityDIY]

oh do display settings need to be in settings.toml now?

[FoamyGuy]

Only certain devices support it I think, it's pretty new I believe. The Metro RP2350 / Fruit Jam are the only ones I know of that do for sure.

It's documented here: https://docs.circuitpython.org/en/latest/docs/environment.html#circuitpy-display-width-circuitpy-display-height-and-circuitpy-display-color-depth-rp2350-boards-with-dvi-or-hstx-connector

It's quite convenient for my situation where the default resolution of CircuitPython isn't supported by the display it's plugged in to.

[FoamyGuy]

This gets considerably better using WAV files with lower sample rate and bit_depth. I re-exported StreetChicken.wav at 8k sample rate and 8 bit depth and it is able to run cleanly to my ear with the animations from this reproducer.

The fruit jam boot jingle + animation is still a bit too much for it to handle though. It's a lot better sounding than it was, but still with noticeable extra static.

I attempted overclocking the CPU but I either did that wrong, or there is something about the Fruit Jam making that not work the same. I tried microcontroller.cpu.frequency = 200_000_000 and it led to weird characters being output and then hard crash and reboot into safe mode.