Fix Si4684 pitch distortion: uncalibrated crystal (CTUN/XTAL_FREQ)
Root cause of FM/DAB "stonata" audio: xtalCtun=31/nominal XTAL_FREQ defaults were never measured against this board's actual crystal (Abracon ABM8-19.200MHZ-10-1-U-T, CL=10pF, two external 15pF load caps). Fixed via CTUN trim by ear (31->0) plus a new live calibration loop that reads the Si4684's own FM_RSQ FREQOFF field (broadcast carriers are GPS-locked, so it's a free precision frequency reference) to trim XTAL_FREQ with no lab equipment. Converged to CTUN=0, XTAL_FREQ=19199750 Hz, residual -3/-4 ppm cross-checked on two stations. New tools/infrastructure (kept, not one-off): - Si4684Driver::recalibrateXtal() + POST /api/tuner/xtal-calibrate: live crystal re-trim without an ESP32 reflash. - FM_RSQ FREQOFF exposed as "freqoff_ppm" in GET /api/tuner/status. - tools/si4684_xtal_calibration.py: automates the trim loop. - tools/si4684_antenna_calibration.py: AN851 Appendix A ANTCAP/VARM/VARB sweep tool (same session, separate calibration). - CONFIG_ESP32_I2S_TEST_TONE (off by default): isolates Si4684-specific audio issues from shared-downstream ones by writing a tone directly over the I2S bus the Si4684 also uses. - SIGMA_WRITE_REGISTER_BLOCK/sigma_safeload_block now retry on NACK and verify via read-back instead of firing I2C writes blind. - FM de-emphasis set to European 50us (was left at the US 75us default). - DAB_ACF_ENABLE restored to its previous 0x0000 with a citation explaining why (tested the datasheet default of 0x0003, made things audibly worse). See docs/si4684-rf-investigation-report.md's 2026-08-23 entry for the full elimination chain and docs/TODO.md for follow-up work (persisting calibration results to EEPROM instead of requiring a firmware edit). Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
This commit is contained in:
Claude Sonnet 5
@@ -8,6 +8,7 @@ idf_component_register(
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"antenna_calibration.cpp"
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"$<$<BOOL:${CONFIG_TEST_FIRMWARE}>:test_firmware.cpp>"
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"$<$<BOOL:${CONFIG_I2S_SDATA_PROBE}>:i2s_sdata_probe.cpp>"
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"$<$<BOOL:${CONFIG_ESP32_I2S_TEST_TONE}>:esp32_i2s_test_tone.cpp>"
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INCLUDE_DIRS "."
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REQUIRES core net secure_store adau1701 si4684 tuner audio bt1035 bluetooth station integration ota eeprom24aa webradio driver
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PRIV_REQUIRES esp_timer esp_http_client
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@@ -17,4 +17,17 @@ config I2S_SDATA_PROBE
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input trace (or an equivalent test point) -- enabling this without the
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rewire just reads whatever GPIO16 happens to be floating/connected to.
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config ESP32_I2S_TEST_TONE
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bool "ESP32-generated sine tone over the shared I2S TX channel"
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default n
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help
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Continuously writes a sine wave to esp32_i2s_sink (the same shared
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BCLK/LRCLK the Si4684 uses on its own SDATA_IN0 pin, but over
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SDATA_IN1). Diagnostic: if this sounds clean while FM/DAB is
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distorted, the ADAU1701's I2S input receiving is fine in general and
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the problem is specific to the Si4684 side. Remember the ESP32
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mixer channel is muted (-96 dB) by default in the stored audio
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profile -- raise it via PUT /api/audio/profile to actually hear
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this.
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endmenu
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@@ -11,14 +11,28 @@
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#include "antenna_calibration.hpp"
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#include "hardware_bootstrap.hpp"
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#include "si4684/Si4684Tuner.hpp"
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namespace antenna_calibration {
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namespace {
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/** Diagnostic-only, 2026-08-23: see net::AntennaCalibration::recalibrateXtal. */
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bool recalibrateXtal(std::uint8_t ibias, std::uint8_t ctun,
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std::uint32_t xtalFreqHz)
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{
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return static_cast<bool>(hardware::HardwareBootstrap::si4684Tuner()
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.recalibrateXtal(ibias, ctun, xtalFreqHz));
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}
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} // namespace
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net::AntennaCalibration& bridge() noexcept
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{
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static net::AntennaCalibration instance{
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.save = &hardware::HardwareBootstrap::saveFmAntCapCalibration,
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.saveDab = &hardware::HardwareBootstrap::saveDabAntCapCalibration,
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.recalibrateXtal = &recalibrateXtal,
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};
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return instance;
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}
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@@ -0,0 +1,57 @@
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/**
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* @file esp32_i2s_test_tone.cpp
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* @brief esp32_i2s_test_tone implementation.
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*
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* DigiRadio firmware — https://github.com/manvalan/DigiRadio
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*
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* Copyright 2026 Michele Bigi
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* SPDX-License-Identifier: Apache-2.0
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*/
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#include "esp32_i2s_test_tone.hpp"
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#include "esp32_i2s_sink.hpp"
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#include <cmath>
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#include <cstdint>
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#include <numbers>
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namespace esp32_i2s_test_tone {
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namespace {
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constexpr int kSampleRateHz = 48000;
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constexpr int kFramesPerBlock = 256;
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/** writeSamples() wants top-aligned 24-bit in a 32-bit slot -- 8-bit shift. */
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constexpr int kTopAlignShift = 8;
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/** Modest amplitude: audible but not a full-scale blast. */
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constexpr float kAmplitude = 0.4F * 8388607.0F;
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constexpr float kTwoPi = 2.0F * std::numbers::pi_v<float>;
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} // namespace
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[[noreturn]] void run(float freqHz)
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{
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esp32_i2s_sink::tryAcquire();
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const float phaseStep = kTwoPi * freqHz / static_cast<float>(kSampleRateHz);
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float phase = 0.0F;
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std::int32_t buf[kFramesPerBlock * 2];
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for (;;)
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{
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for (int i = 0; i < kFramesPerBlock; ++i)
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{
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phase += phaseStep;
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if (phase > kTwoPi)
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{
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phase -= kTwoPi;
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}
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const auto sample =
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static_cast<std::int32_t>(std::sin(phase) * kAmplitude)
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<< kTopAlignShift;
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buf[(i * 2) + 0] = sample;
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buf[(i * 2) + 1] = sample;
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}
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esp32_i2s_sink::writeSamples(buf, kFramesPerBlock * 2);
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}
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}
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} // namespace esp32_i2s_test_tone
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@@ -0,0 +1,28 @@
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/**
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* @file esp32_i2s_test_tone.hpp
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* @brief Continuous sine tone over the shared ESP32 -> ADAU1701 I2S TX
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* channel, for isolating ADAU1701 I2S-input problems from the
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* Si4684 specifically.
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*
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* DigiRadio firmware — https://github.com/manvalan/DigiRadio
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*
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* Copyright 2026 Michele Bigi
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* SPDX-License-Identifier: Apache-2.0
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*/
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#pragma once
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namespace esp32_i2s_test_tone {
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/**
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* Generate and write a sine-wave tone over esp32_i2s_sink forever. Intended
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* to run as its own FreeRTOS task (never returns). Unlike the ADAU1701's
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* internal Beep cell (POST /api/audio/beep), this tone travels over the
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* physical SDATA_IN1 wire and the shared BCLK/LRCLK the Si4684 also uses on
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* SDATA_IN0 -- if it sounds clean while FM/DAB is distorted, the problem is
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* specific to the Si4684 side, not the ADAU1701's I2S input path in general.
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*
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* @param freqHz Tone frequency in Hz.
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*/
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[[noreturn]] void run(float freqHz);
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} // namespace esp32_i2s_test_tone
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@@ -160,7 +160,21 @@ std::expected<void, HardwareBootError> HardwareBootstrap::boot()
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return {};
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}
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if (auto tunerResult = gSi4684.boot(si4684::Si4684Band::Dab); !tunerResult) {
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// xtalCtun=0, xtalFreqHz=19199750 (2026-08-23): the compiled-in
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// defaults (ctun=31, xtal=19200000 nominal) were never measured
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// against this board's actual crystal (Abracon ABM8-19.200MHZ-10-1-U-T,
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// CL=10pF per part number, plus two external 15pF load caps per the
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// schematic). CTUN=0 was found audibly best via A/B listening (0/5/31),
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// then xtalFreqHz was trimmed properly using the chip's own FM_RSQ
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// FREQOFF measurement (tools/si4684_xtal_calibration.py) against two
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// real, GPS-locked broadcast carriers 87.6/105.1 MHz -- converged to
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// -3 to -4 ppm residual on both (cross-check confirms it's the
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// crystal, not something frequency-dependent), down from +70 ppm
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// uncorrected. See POST /api/tuner/xtal-calibrate to re-trim live if
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// this ever needs revisiting (e.g. after a board/crystal change).
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if (auto tunerResult =
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gSi4684.boot(si4684::Si4684Band::Dab, 72U, 0U, 19199750U);
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!tunerResult) {
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ESP_LOGE(kTag, "Si4684 boot failed: error %d", static_cast<int>(tunerResult.error()));
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return std::unexpected(HardwareBootError::Si4684BootFailed);
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}
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@@ -45,6 +45,10 @@
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#include "i2s_sdata_probe.hpp"
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#endif
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#if CONFIG_ESP32_I2S_TEST_TONE
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#include "esp32_i2s_test_tone.hpp"
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#endif
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namespace {
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constexpr char kTag[] = "digiradio";
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@@ -133,6 +137,14 @@ void heartbeatTask(void* arg)
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}
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}
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#if CONFIG_ESP32_I2S_TEST_TONE
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[[noreturn]] void i2sTestToneTask(void* arg)
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{
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(void)arg;
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esp32_i2s_test_tone::run(440.0F);
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}
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#endif
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} // namespace
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/**
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@@ -213,6 +225,13 @@ extern "C" void app_main()
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"streaming will be unavailable");
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}
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#if CONFIG_ESP32_I2S_TEST_TONE
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if (xTaskCreate(i2sTestToneTask, "i2s_test_tone", 4096, nullptr, 4,
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nullptr) != pdPASS) {
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ESP_LOGW(kTag, "ESP32 I2S test tone task create failed");
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}
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#endif
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auto netResult = net::NetBootstrap::start(
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store,
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tunerService,
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