shawn
0ae2ca6e8e
Custom I2S HAT for Pi Multi-FX Pedal — full hardware package: - KiCad project: schematic (kicad_sch), PCB layout (kicad_pcb), project file - Custom DT overlay: pcm1808-pcm5102-overlay.dts (no upstream overlay exists for PCM1808) - docs/hardware-bom.md: BOM (9.25 HAT + 1.75 with enclosure), wiring diagram, PCB design notes - docs/config-audio.md: DT overlay build, ALSA config, JACK integration, troubleshooting - scripts/install_hat.sh: One-command install + test suite (6 tests) - hardware/gerber/: JLCPCB fab instructions and assembly notes Circuit: Guitar input → TL072 preamp (gain ~20dB) → PCM1808 ADC → RPi I2S → PCM5102 DAC → RC filter → output jack I2S: BCLK/GPIO18, LRCLK/GPIO19, DIN/GPIO20, DOUT/GPIO21 Stacking header passes all 40 GPIO pins for footswitches/LEDs/display
294 lines
7.0 KiB
Markdown
294 lines
7.0 KiB
Markdown
# Audio Configuration — PCM1808+PCM5102 I2S HAT
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> **HAT:** Custom PCM1808 ADC + PCM5102 DAC I2S audio HAT
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> **RPi:** 4B, Raspberry Pi OS (Bookworm, 64-bit)
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> **Kernel:** rpi-6.6.y (upstream Raspberry Pi kernel)
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> **Last updated:** 2026-06-07
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---
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## Device Tree Overlay
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The PCM1808 ADC has **no upstream overlay** in the rpi-6.6.y kernel tree. A custom overlay is provided at:
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```
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hardware/pcm1808-pcm5102-overlay.dts
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```
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### Build & Install
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```bash
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# Install device-tree-compiler if not present
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sudo apt-get install device-tree-compiler
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# Compile overlay
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dtc -@ -I dts -O dtb -o pcm1808-pcm5102-overlay.dtbo \
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hardware/pcm1808-pcm5102-overlay.dts
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# Copy to boot overlays directory
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sudo cp pcm1808-pcm5102-overlay.dtbo /boot/firmware/overlays/
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# On older Pi OS: /boot/overlays/
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```
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This compiles to `/boot/firmware/overlays/pcm1808-pcm5102-overlay.dtbo`.
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### Enable Overlay
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Edit `/boot/firmware/config.txt` (or `/boot/config.txt` on older installs):
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```ini
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# ── Custom I2S HAT: PCM1808 ADC + PCM5102 DAC ─────────
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dtoverlay=pcm1808-pcm5102-overlay
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# Disable onboard audio to free I2S pins
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dtparam=audio=off
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# Optional: force I2S pins if overlay doesn't set them
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# dtparam=i2s=on
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```
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### Verify Overlay Loads
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```bash
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# Check overlay is loaded
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dmesg | grep -i "pcm1808\|pcm5102\|i2s"
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# Check ALSA sees both devices
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aplay -l
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arecord -l
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# Expected output for playback:
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# card 0: pcm1808pcm5102hat [pcm1808-pcm5102-hat], device 0: ... []
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# Subdevices: 1/1
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# Expected output for capture:
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# card 0: pcm1808pcm5102hat [pcm1808-pcm5102-hat], device 0: ... []
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# Subdevices: 1/1
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# Check /proc device tree
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cat /proc/device-tree/sound/name # should show "pcm1808-pcm5102-hat"
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```
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---
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## ALSA Configuration
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### Default Card Setup
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Create `/etc/asound.conf` (system-wide) or `~/.asoundrc` (per-user):
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```conf
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# ── PCM1808+PCM5102 I2S HAT ─────────────────────────
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# Default playback device
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pcm.!default {
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type asym
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playback.pcm {
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type hw
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card 0
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device 0
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}
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capture.pcm {
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type hw
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card 0
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device 0
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}
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}
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# Hardware device aliases
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pcm.i2s_playback {
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type hw
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card 0
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device 0
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}
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pcm.i2s_capture {
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type hw
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card 0
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device 0
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}
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# Software volume control (PCM1808/PCM5102 have no HW volume)
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pcm.softvol_playback {
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type softvol
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slave.pcm "i2s_playback"
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control {
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name "Master Playback Volume"
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card 0
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}
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min_dB -50.0
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max_dB 0.0
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}
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# 48kHz upsampler for 44.1kHz sources (like YouTube/Spotify)
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pcm.rate_convert {
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type plug
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slave {
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pcm "softvol_playback"
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rate 48000
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format S24_3LE
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channels 2
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}
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}
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# Default: use rate conversion + softvol
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pcm.!default {
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type plug
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slave.pcm "rate_convert"
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}
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# Control device
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ctl.!default {
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type hw
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card 0
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}
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```
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### Test Audio
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```bash
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# --- Playback test ---
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# Sine wave at 440Hz (A4)
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speaker-test -t sine -f 440 -l 1 -c 2
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# Play a WAV file
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aplay /usr/share/sounds/alsa/Front_Center.wav
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# --- Capture test ---
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# Record 3 seconds from ADC
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arecord -d 3 -f cd -t wav test_record.wav
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# Play back the recording
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aplay test_record.wav
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# --- Full loopback test ---
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# Play tone while recording (connect DAC output to ADC input)
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# Check latency: <10ms at 48kHz/128 frames
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arecord -d 5 -f S24_3LE -r 48000 -c 2 loopback_test.wav &
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speaker-test -t sine -f 440 -l 2
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wait
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aplay loopback_test.wav
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```
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---
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## JACK Audio Configuration
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The pedal DSP runs under JACK. The existing JACK config in `main.py` uses `hw:1,0` (USB). Swap to `hw:0,0` for I2S:
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### JACK Start
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```bash
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# Kill PulseAudio (conflicts with JACK on RPi)
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pulseaudio --kill
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# Start JACK at 48kHz/128 frames (recommended target: ~5.3ms buffer)
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jackd -R -d alsa \
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-d hw:0,0 \
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-r 48000 \
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-p 128 \
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-n 3
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# For low-latency mode (risky, check xruns):
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jackd -R -d alsa -d hw:0,0 -r 48000 -p 64 -n 2
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```
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### Update main.py Config
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In `/home/oplabs/projects/pi-multifx-pedal/main.py`, change:
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```python
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# FROM (USB Audio):
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# config = {
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# "input_device": "hw:1,0",
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# "output_device": "hw:1,0",
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# }
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# TO (I2S HAT):
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config = {
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"input_device": "hw:0,0", # PCM1808 ADC
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"output_device": "hw:0,0", # PCM5102 DAC
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"sample_rate": 48000,
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"period_size": 128, # 2.6ms buffer
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"num_periods": 3, # triple-buffered
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}
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```
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---
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## Integration with NAM DSP
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The I2S HAT uses the **same block size** as the NAM DSP engine (256 samples):
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| Parameter | Value | Note |
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|-----------|-------|------|
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| Sample rate | 48,000 Hz | Both JACK and NAM |
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| Block size | 256 frames | NAM internal block |
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| JACK period | 128 frames | 2 × periods per block |
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| Round-trip (target) | <8ms | 128fr × 2 + codec delay + DSP |
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At 48kHz/128 frames × 3 periods = ~8ms round-trip, well within the 10ms target for NAM DSP. The 256-sample NAM block fits exactly into 2 JACK periods.
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---
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## Troubleshooting
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### No card 0 detected
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```bash
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# Check if I2S is enabled in pin controller
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dmesg | grep -i i2s
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# Check loaded overlays
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vcgencmd get_config dtov
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# Should show: pcm1808-pcm5102-overlay
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# Rebuild overlay if kernel was updated
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sudo dtc -@ -I dts -O dtb -o /boot/firmware/overlays/pcm1808-pcm5102-overlay.dtbo \
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/home/oplabs/projects/pi-multifx-pedal/hardware/pcm1808-pcm5102-overlay.dts
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```
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### No capture device
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PCM1808 has no upstream overlay — the custom overlay provides the `pcm1808` codec binding. If capture isn't showing:
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```bash
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# Verify the overlay node compiled
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dtc -I dtb -O dts /boot/firmware/overlays/pcm1808-pcm5102-overlay.dtbo | grep -i pcm1808
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# Check I2S pin muxing is correct
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raspi-gpio get 18 19 20 21
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# Expect: GPIO 18: level=0 func=ALT5 (I2S BCLK)
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# GPIO 19: level=0 func=ALT5 (I2S LRCLK)
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# GPIO 20: level=0 func=ALT5 (I2S DIN)
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# GPIO 21: level=0 func=ALT5 (I2S DOUT)
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```
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### PCM5102 hiss
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- Add 330Ω + 10µF RC filter on DAC output (R5, C10 in BOM)
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- Ensure XSMT (pin 17) is pulled to 3.3V, not floating
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- Check 3.3V rail noise with oscilloscope (<50mV ripple at audio frequencies)
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### JACK xruns
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- Increase period size: `-p 256` (5.3ms, safer)
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- Increase num periods: `-n 3` (triple buffer)
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- Isolate RPi 4B from USB power noise
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- Check `cat /proc/asound/card0/pcm0p/sub0/status` for xrun count
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---
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## Pinout Reference
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| Signal | BCM GPIO | Physical Pin | ALT Function | Direction |
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|--------|----------|:------------:|:------------:|:---------:|
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| BCLK | GPIO18 | Pin 12 | ALT5 (I2S) | RPi → HAT |
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| LRCLK | GPIO19 | Pin 35 | ALT5 (I2S) | RPi → HAT |
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| DIN | GPIO20 | Pin 38 | ALT5 (I2S) | HAT → RPi |
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| DOUT | GPIO21 | Pin 40 | ALT5 (I2S) | RPi → HAT |
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| 3.3V | — | Pins 1, 17 | Power | RPi → HAT |
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| 5V | — | Pins 2, 4 | Power | RPi → HAT |
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| GND | — | Pins 6, 9, 14, 25, 30, 34, 39 | Ground | — |
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The I2S HAT uses a **stacking header** (2×20 female socket) to pass through all 40 GPIO pins so footswitches, LEDs, and display are accessible from the top of the HAT. |