Two independent bugs silenced the digital audio path from Si4684 into the
ADAU1701 even after the FM/DAB tune fix produced a real RF lock:
1. Si4684Driver::configureAfterBoot() wrote PIN_CONFIG_ENABLE (0x0800) as
0x0003, enabling both I2SOUTEN and DACOUTEN. AN649: "only I2SOUTEN or
DACOUTEN can be enabled at a time. If both enabled, only analog audio
output is enabled" — the chip silently fell back to its unused analog
DAC output on every boot. Fixed to 0x8002 (I2SOUTEN + INTBOUTEN),
matching the value hitech95/si468x_dab_receiver's working ALSA codec
driver uses (SI468X_PROP_I2S_ENABLED); I2SOUTEN alone (0x0002) was not
sufficient on this hardware. Also fixed AUDIO_OUTPUT_CONFIG (0x0302),
which was being written with a stray I2S-enable bit that property does
not have (its only real field is bit0 MONO).
2. Even with the chip correctly outputting I2S, the ADAU1701 received only
static. Traced with SIGMA_WRITE_REGISTER_BLOCK live overrides of
SerialInputRegister (0x081F, baked into the compiled SigmaStudio export
at ILP=0/IBP=0): IBP=1 (input data clocked on the opposite BCLK edge)
produced real, recognizable music instead of static on a locked, strong
FM signal — first confirmed end-to-end audio in this project's history.
ILP=1 made it worse and was reverted; IBP=1 kept as a runtime override
in Adau1701Driver::boot().
Remaining noise on top of the music is attributed to antenna quality
(RSSI/SNR fluctuated significantly between retunes of the same station on
the current improvised antenna) — not yet confirmed with a proper antenna.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0178rASQ6ZETPMUamvpoR2KR
micheleandClaude Sonnet 5
6974095f35