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Fix Si4684 I2S audio: PIN_CONFIG_ENABLE conflict + ADAU1701 BCLK polarity

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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
This commit is contained in:
michele
2026-08-16 01:12:57 +02:00
co-authored by Claude Sonnet 5
parent f5fe92f93e
commit 6974095f35
3 changed files with 104 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files
Software/components/drivers/si4684/src/Si4684Driver.cpp
+15 -5
View File
@@ -56,8 +56,11 @@ constexpr std::uint16_t kPropPinConfigEnable = 0x0800U;
constexpr std::uint16_t kPropAudioVolume = 0x0300U;
constexpr std::uint16_t kPropAudioMute = 0x0301U;
constexpr std::uint16_t kPropAudioOutputConfig = 0x0302U;
/** AN649 AUDIO_OUTPUT_CONFIG bit1 I2SOUTEN — required for I2S to ADAU1701. */
constexpr std::uint16_t kSi4684I2sOutEnable = 0x0002U;
/** AN649 PIN_CONFIG_ENABLE bit1 I2SOUTEN + bit15 INTBOUTEN — matches the
* value used by hitech95/si468x_dab_receiver's working ALSA codec driver
* (SI468X_PROP_I2S_ENABLED = 0x8002); INTBOUTEN alone (0x0002) was not
* sufficient to produce audio on real hardware in this project. */
constexpr std::uint16_t kSi4684I2sOutEnable = 0x8002U;
/** Si4684 volume: 0=mute, 63=max (AN649 AUDIO_ANALOG_VOLUME). */
constexpr std::uint8_t kSi4684VolumeMax = 63U;
constexpr std::uint16_t kPropFmRdsConfig = 0x3C02U;
@@ -560,14 +563,21 @@ std::expected<void, Si4684Error> Si4684Driver::configureAfterBoot(
!rate) {
return rate;
}
if (auto pins = setProperty(kPropPinConfigEnable, 0x0003U); !pins) {
// AN649 Property 0x0800 PIN_CONFIG_ENABLE bit1=I2SOUTEN, bit0=DACOUTEN:
// "only I2SOUTEN or DACOUTEN can be enabled at a time. If both enabled,
// only analog audio output is enabled." We only wire I2S to the
// ADAU1701 (no DAC pins connected), so DACOUTEN must stay 0 or the chip
// silently falls back to analog-only and the I2S bus carries silence.
if (auto pins = setProperty(kPropPinConfigEnable, kSi4684I2sOutEnable);
!pins) {
return pins;
}
if (auto mute = setProperty(kPropAudioMute, 0x0000U); !mute) {
return mute;
}
if (auto outCfg = setProperty(kPropAudioOutputConfig, kSi4684I2sOutEnable);
!outCfg) {
// AN649 Property 0x0302 AUDIO_OUTPUT_CONFIG bit0=MONO (all other bits
// reserved, must be 0). Not an I2S enable — that lives at 0x0800 above.
if (auto outCfg = setProperty(kPropAudioOutputConfig, 0x0000U); !outCfg) {
return outCfg;
}
if (auto vol = setProperty(kPropAudioVolume, kSi4684VolumeMax); !vol) {