Add BT1035 driver with manual chapter and expand Si4684 tuning docs.

Implement Bt1035Driver AT init (AT+AUXCFG=1), core AT parser with host tests,
wire boot into HardwareBootstrap, and document DAB/FM tuning workflows in ch-si4684.

Co-authored-by: Cursor <cursoragent@cursor.com>

Software/components/core/CMakeLists.txt

@@ -22,6 +22,7 @@ idf_component_register(
         "src/EnhancementsDesign.cpp"
         "src/AudioProfile.cpp"
         "src/AudioProfileJson.cpp"
+        "src/Bt1035At.cpp"
     INCLUDE_DIRS "include"
 )
 

Software/components/core/include/core/Bt1035At.hpp

@@ -0,0 +1,99 @@
+/**
+ * @file    Bt1035At.hpp
+ * @brief   Typed AT command builder and response parser for FSC-BT1035.
+ *
+ * DigiRadio firmware — https://github.com/manvalan/DigiRadio
+ *
+ * Copyright 2026 Michele Bigi
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * @author  Michele Bigi
+ * @date    2026-07-06
+ */
+#pragma once
+
+#include "core/ParseError.hpp"
+
+#include <array>
+#include <cstddef>
+#include <expected>
+#include <string>
+#include <string_view>
+
+namespace core {
+
+/**
+ * @brief    Bt1035AtCommand — supported AT commands (enumerated subset).
+ *
+ * @dname    Bt1035AtCommand
+ * @return   n/a (type)
+ * @pubstate Each variant maps to one line via buildBt1035AtLine().
+ *
+ * @author   Michele Bigi
+ * @date     2026-07-06
+ */
+enum class Bt1035AtCommand {
+    Ping,      ///< AT — link check.
+    AuxLineIn, ///< AT+AUXCFG=1 — wired Line-In from ADAU1701 (mandatory).
+};
+
+/**
+ * @brief    Bt1035AtResponseKind — parsed module reply class.
+ *
+ * @dname    Bt1035AtResponseKind
+ * @return   n/a (type)
+ * @pubstate Unknown payloads map to Unexpected, never ignored.
+ *
+ * @author   Michele Bigi
+ * @date     2026-07-06
+ */
+enum class Bt1035AtResponseKind {
+    Ok,
+    Error,
+    Unexpected,
+};
+
+/** Number of commands in bootInitSequence(). */
+inline constexpr std::size_t kBt1035BootInitCommandCount = 2U;
+
+/**
+ * @brief    buildBt1035AtLine — serialise a command with CRLF terminator.
+ *
+ * @dname    buildBt1035AtLine
+ * @param    command  Typed AT command.
+ * @return   Full line including \r\n suffix.
+ * @pubstate none
+ *
+ * @author   Michele Bigi
+ * @date     2026-07-06
+ */
+[[nodiscard]] std::string buildBt1035AtLine(Bt1035AtCommand command);
+
+/**
+ * @brief    bootInitSequence — mandatory bring-up commands in order.
+ *
+ * @dname    bootInitSequence
+ * @return   Ping then AuxLineIn (AT+AUXCFG=1).
+ * @pubstate none
+ *
+ * @author   Michele Bigi
+ * @date     2026-07-06
+ */
+[[nodiscard]] std::array<Bt1035AtCommand, kBt1035BootInitCommandCount>
+bootInitSequence() noexcept;
+
+/**
+ * @brief    parseBt1035AtResponse — classify a single response line.
+ *
+ * @dname    parseBt1035AtResponse
+ * @param    line  Untrusted UART payload (may include whitespace).
+ * @return   Ok, Error, or Unexpected.
+ * @pubstate none
+ *
+ * @author   Michele Bigi
+ * @date     2026-07-06
+ */
+[[nodiscard]] Bt1035AtResponseKind parseBt1035AtResponse(
+    std::string_view line) noexcept;
+
+} // namespace core

Software/components/core/src/Bt1035At.cpp

@@ -0,0 +1,68 @@
+/**
+ * @file    Bt1035At.cpp
+ * @brief   Bt1035At implementation.
+ *
+ * DigiRadio firmware — https://github.com/manvalan/DigiRadio
+ *
+ * Copyright 2026 Michele Bigi
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * @author  Michele Bigi
+ * @date    2026-07-06
+ */
+
+#include "core/Bt1035At.hpp"
+
+namespace core {
+
+namespace {
+
+[[nodiscard]] std::string_view trimAscii(std::string_view text) noexcept
+{
+    while (!text.empty()
+           && (text.front() == ' ' || text.front() == '\r'
+               || text.front() == '\n' || text.front() == '\t')) {
+        text.remove_prefix(1U);
+    }
+    while (!text.empty()
+           && (text.back() == ' ' || text.back() == '\r' || text.back() == '\n'
+               || text.back() == '\t')) {
+        text.remove_suffix(1U);
+    }
+    return text;
+}
+
+} // namespace
+
+std::string buildBt1035AtLine(Bt1035AtCommand command)
+{
+    switch (command) {
+    case Bt1035AtCommand::Ping:
+        return "AT\r\n";
+    case Bt1035AtCommand::AuxLineIn:
+        return "AT+AUXCFG=1\r\n";
+    }
+    return "AT\r\n";
+}
+
+std::array<Bt1035AtCommand, kBt1035BootInitCommandCount> bootInitSequence() noexcept
+{
+    return std::array<Bt1035AtCommand, kBt1035BootInitCommandCount>{
+        Bt1035AtCommand::Ping,
+        Bt1035AtCommand::AuxLineIn,
+    };
+}
+
+Bt1035AtResponseKind parseBt1035AtResponse(std::string_view line) noexcept
+{
+    const std::string_view trimmed = trimAscii(line);
+    if (trimmed == "OK") {
+        return Bt1035AtResponseKind::Ok;
+    }
+    if (trimmed == "ERROR" || trimmed.starts_with("ERROR")) {
+        return Bt1035AtResponseKind::Error;
+    }
+    return Bt1035AtResponseKind::Unexpected;
+}
+
+} // namespace core

Software/components/core/test/CMakeLists.txt

@@ -34,6 +34,7 @@ add_library(digiradio_core STATIC
     "${CORE_SRC_DIR}/EnhancementsDesign.cpp"
     "${CORE_SRC_DIR}/AudioProfile.cpp"
     "${CORE_SRC_DIR}/AudioProfileJson.cpp"
+    "${CORE_SRC_DIR}/Bt1035At.cpp"
 )
 target_include_directories(digiradio_core PUBLIC
     "${CMAKE_CURRENT_SOURCE_DIR}/../include"
@@ -70,3 +71,7 @@ add_test(NAME audio_profile_json_test COMMAND audio_profile_json_test)
 add_executable(enhancements_design_test enhancements_design_test.cpp)
 target_link_libraries(enhancements_design_test PRIVATE digiradio_core)
 add_test(NAME enhancements_design_test COMMAND enhancements_design_test)
+
+add_executable(bt1035_at_test bt1035_at_test.cpp)
+target_link_libraries(bt1035_at_test PRIVATE digiradio_core)
+add_test(NAME bt1035_at_test COMMAND bt1035_at_test)

Software/components/core/test/bt1035_at_test.cpp

@@ -0,0 +1,71 @@
+/**
+ * @file    bt1035_at_test.cpp
+ * @brief   Host tests for FSC-BT1035 AT command builder and parser.
+ *
+ * DigiRadio firmware — https://github.com/manvalan/DigiRadio
+ *
+ * Copyright 2026 Michele Bigi
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * @author  Michele Bigi
+ * @date    2026-07-06
+ */
+
+#include "core/Bt1035At.hpp"
+
+#include <cstdlib>
+#include <iostream>
+#include <string>
+
+namespace {
+
+[[nodiscard]] int runInitSequenceTest()
+{
+    const auto sequence = core::bootInitSequence();
+    if (sequence.size() != core::kBt1035BootInitCommandCount) {
+        std::cerr << "init sequence size mismatch\n";
+        return EXIT_FAILURE;
+    }
+    if (sequence[1U] != core::Bt1035AtCommand::AuxLineIn) {
+        std::cerr << "AUXCFG=1 must be in init sequence\n";
+        return EXIT_FAILURE;
+    }
+    const std::string aux = core::buildBt1035AtLine(core::Bt1035AtCommand::AuxLineIn);
+    if (aux != "AT+AUXCFG=1\r\n") {
+        std::cerr << "AUXCFG command line mismatch\n";
+        return EXIT_FAILURE;
+    }
+    return EXIT_SUCCESS;
+}
+
+[[nodiscard]] int runParseTest()
+{
+    if (core::parseBt1035AtResponse("OK\r\n") != core::Bt1035AtResponseKind::Ok) {
+        std::cerr << "OK parse failed\n";
+        return EXIT_FAILURE;
+    }
+    if (core::parseBt1035AtResponse("ERROR\r\n")
+        != core::Bt1035AtResponseKind::Error) {
+        std::cerr << "ERROR parse failed\n";
+        return EXIT_FAILURE;
+    }
+    if (core::parseBt1035AtResponse("garbage")
+        != core::Bt1035AtResponseKind::Unexpected) {
+        std::cerr << "unexpected parse failed\n";
+        return EXIT_FAILURE;
+    }
+    return EXIT_SUCCESS;
+}
+
+} // namespace
+
+int main()
+{
+    if (runInitSequenceTest() != EXIT_SUCCESS) {
+        return EXIT_FAILURE;
+    }
+    if (runParseTest() != EXIT_SUCCESS) {
+        return EXIT_FAILURE;
+    }
+    return EXIT_SUCCESS;
+}