i2s stereo is reversed in Raspberry Pi Pico

[VinceParsons]

CircuitPython version and board name

Verified on 8.x, 9.x, and even the 10 pre-releases. raspberry_pi_pico_w, but also verified on a pico 2w.

Code/REPL

import board
import audiobusio
import audiocore
import time

audioOut = audiobusio.I2SOut(bit_clock=board.GP8, word_select=board.GP9, data=board.GP7)
sound = audiocore.WaveFile("leftright.wav")
audioOut.play(sound)

while audioOut.playing:
	time.sleep(1)
	
print("done")

Behavior

No error messages, but left and right channels are reversed. The same code (pins adjusted, of course) on a WaveShare ESP32-S3-Zero works correctly.

Description

Only tried on i2s, not PWM audio. Is reversed whether or not a mixer is used, or whether file is .wav or .mp3.

Additional information

No response

[tannewt]

We can probably modify the PIO I2SOutput code to change the word select polarity and it'll be fixed. I'm not sure we ever checked this.

[dhalbert]

I tested with a Metro RP2040 and a two-channel I2S audio amp (Adafruit Pi Speaker Bonnet). The channels are swapped most of the time but not quite all the time. There are actually four different PIO programs in the code: two for left_justified or not, and two for swapping the order of bit_clock and word_select or not. Those two pins must be consecutive, but we allow them to be in either order.

bit_clock	word_select	left_justified	Left/Right swapped	using swapped bit_clock/word_select pins program
D2	D3	False	swapped	-
D3	D2	False	correct	swapped-pin program
D2	D3	True	swapped	-
D3	D2	True	swapped	swapped-pin program

It is not clear to me what left_justified is actually doing, because the output sounds the same. There are PIO program differences, though.

(Side comment: At first I tested with a UDA1134 stereo amp, and got terrible noise on one channel when there was any signal on that channel. This is odd and is a completely separate issue. The problem was confined to RP2040 + UDA1334. The UDA1334 worked OK with a SAMD51 doing I2S. Maybe this is a missing pull or something like that.)