USB Audio Testing Plan

usb-plan.md

USB Audio Testing Plan

Platform × Direction (core tests)

#	Platform	Mode	Key settings	Test
1	ESP32	TX	defaults (enable_multi_sample_rate=false)	Record 5s with arecord, play back, verify clean sine
2	ESP32	RX	defaults	Play test.wav with aplay, verify rxXfer > 0, MeasuringStream output
3	ESP32	RXTX	enable_ep_in=true, enable_ep_out=true	Record AND play simultaneously
4	RP2040	TX	defaults	Record with arecord, verify clean sine
5	RP2040	RX	defaults	Play with aplay, verify data received
6	RP2040	RXTX	both directions	Simultaneous record + play

Audio format variations

#	Setting	Values to test	Verify
7	sample_rate	44100, 48000	Correct playback speed, frame matches rate
8	channels	1 (mono), 2 (stereo)	lsusb shows correct bNrChannels, arecord -c N works
9	bits_per_sample	16, 24	lsusb shows correct bSubslotSize, arecord -f S16/S24_3LE

Feature flags

#	Flag	Test with true	Test with false	Verify
10	enable_feedback_ep	TX only (no effect), RX with feedback	RX without feedback	lsusb shows/hides feedback EP, aplay works
11	enable_multi_sample_rate	Host can change rate, 14 rates in GET_RANGE	Fixed rate, single rate in GET_RANGE	lsusb clock type (fixed vs programmable), no dmesg errors
12	enable_interrupt_ep	AC interface has interrupt EP	No interrupt EP	lsusb shows/hides interrupt EP, device enumerates
13	enable_ep_in_flow_control	Frame sizes vary (176/180 for 44100)	Fixed frame size	frame diagnostic matches expectation
14	volume_active	processVolume scales audio	Volume/mute info only, no processing	Set volume to 50% via amixer, verify level change (true) or no change (false)

Composite device (CDC + Audio)

#	Configuration	Verify
15	ESP32: USBCDC USBSerial + Audio TX	Both CDC serial and audio work, no EP conflicts
16	ESP32: USBCDC USBSerial + Audio RX	Both CDC serial and audio work
17	RP2040: Audio only (no CDC)	Enumeration, TX/RX work

Buffering

#	Setting	Values	Verify
18	fifo_packets	8, 16, 32	Audio quality (smaller = more glitch-prone), RAM usage
19	ESP32 SynchronizedNBufferRTOS	default (5ms write wait)	No write failures, clean audio
20	RP2040 RingBuffer	default	Write retry loop works, clean audio

Volume / Mute controls

#	Test	Verify
21	amixer -c Audio shows Mic/Speaker controls	Volume range -100dB to 0dB, mute on/off
22	Host changes volume via amixer	setVolumeCallback fires, getVolume() returns new value
23	Host changes mute via amixer	setMuteCallback fires, isMute() returns new value
24	Device changes volume via setVolume(0.5)	Host sees updated value on next GET_CUR

Edge cases

#	Test	Verify
25	USB disconnect/reconnect during streaming	No crash, streaming resumes after reconnect
26	Start/stop streaming repeatedly (open/close Audacity 5×)	No memory leak, active toggles correctly
27	begin() called twice	No crash, second call is no-op
28	aplay with wrong format (-f S32_LE)	Clean error, no crash

Host-side test commands

# Record (TX mode test)
arecord -D hw:Audio -f S16_LE -r 44100 -c 2 -d 5 test.wav && aplay test.wav

# Play (RX mode test)
aplay -D hw:Audio -f S16_LE -r 44100 -c 2 test.wav

# Check descriptor
lsusb -v -d cafe:4002

# Check mixer controls
amixer -c Audio

# Check for USB errors
dmesg | tail -20

# List audio devices
aplay -l | grep Audio
arecord -l | grep Audio

Sketch-side diagnostics

// TX diagnostics
MySerial.print("xfer="); MySerial.print(out.getTxXferCount());
MySerial.print(" rd="); MySerial.print(out.getTxFifoReadTotal());
MySerial.print(" avail="); MySerial.print(out.availableForWrite());
MySerial.print(" frame="); MySerial.print(out.getTxFrameBytesLast());
MySerial.print(" bps="); MySerial.println(out.getTxBytesPerSample());

// RX diagnostics
MySerial.print("active="); MySerial.print(in.isStreamingActiveRx());
MySerial.print(" rxXfer="); MySerial.print(in.getRxXferCount());
MySerial.print(" rxBytes="); MySerial.print(in.getRxTotalBytes());
MySerial.print(" bufRx="); MySerial.print(in.bufferRx().available());
MySerial.print(" avail="); MySerial.println(in.available());

Priority order

1. Core tests (1, 2, 4, 5) — TX/RX on both platforms
2. Format variations (7–9) — sample rate, channels, bit depth
3. Feature flags (10–14) — feedback, multi-rate, interrupt EP, flow control, volume
4. Composite (15–17) — CDC + Audio
5. Buffering (18–20) — FIFO depth, buffer types
6. Volume/Mute (21–24) — control requests
7. Edge cases (25–28) — robustness