Sign ITS messages on the ESP32-C5 with vanetza-idf, over USB or BLE

obu-firmware is now a port of the colleague's standalone VRU station
(microbu-esp32c5/firmware, kept beside this repository and gitignored): the
vanetza-idf C-ITS stack with the TS 103 097 security entity, credentials in
NVS, the station-link v1 protocol over the native USB port (frame type 0x10
in the existing 0xAA55 framing) and over a BLE GATT peripheral, and its
ITS-G5 radio adapter. The phone still builds CAM and VAM; the board adds
GeoNetworking/BTP and signs with the provisioned authorization ticket. The
private key never leaves the board. Builds with ESP-IDF 6.0.2 only, which
vanetza-idf pins for the radio's private driver ABI. The previous C firmware
stays on disk unbuilt; a full-flash backup of the bench board is kept in
firmware-backups/ (gitignored).

Changed against the colleague's firmware, marked MicrOBU: in the sources:
- Reception unchanged for the app. vanetza-idf drops what it cannot verify
  (unsigned traffic, every RSU), so each captured frame also goes through the
  previous gn_unwrap.c and reaches the phone as link opcode V2X_RX (0x85),
  whose body is the old SERIAL_MSG_V2X_RX payload.
- Unsigned transmission still possible, with the previous geonet.c header;
  the phone chooses per message.
- Console on UART0 (CH343 port); the native USB port carries only link frames.
- BLE advertising pauses while the USB link is in use: BLE and ITS-G5 share
  one RF front end.
- NVS 80 KB (app at 0x20000). At 24 KB, with Wi-Fi settings the previous
  firmware left behind, the BLE bond could not be stored and the phone had to
  pair on every connection.
- Bench fixes: the radio queue is drained before the first PoTi (no RX and
  ~177 queue drops before); the station loop waited pdMS_TO_TICKS(5) = 0
  ticks at 100 Hz and starved the idle task; the 2.4 KB RX capture buffer is
  off the Wi-Fi task stack; BLE notifications longer than the MTU are dropped
  instead of cut short, MTU 517; serial writes are skipped with no USB host.
- Manual country policy and TX-power read-back from the previous radio setup;
  logs for BLE encryption changes and the number of stored bonds.

Verified on the bench board (COM3) with the phone over USB and BLE: CAM and
VAM, signed and unsigned, go out; reception of the sim car and the RSU's
CAM/SPATEM/MAPEM continues; the board survives app restarts and reconnects.
See docs/06-signed-its-vam-ble.md.

obu-firmware/CMakeLists.txt

@@ -1,9 +1,62 @@
-cmake_minimum_required(VERSION 3.16)
+cmake_minimum_required(VERSION 3.22)
+# obu-firmware: the ESP32-C5 half of the MicrOBU station, on the vanetza-idf C-ITS stack.
+#
+# Since 2026-09-23 this is a port of the colleague's standalone VRU station
+# (microbu-esp32c5/firmware, its own git repository beside this one and gitignored here). From it:
+# BTP/GeoNetworking and the TS 103 097 security entity (vanetza-idf), the station-link message
+# layer over native USB Serial/JTAG and BLE GATT, the NVS credential store, and the C5 radio adapter.
+# Added here for this project: the raw receive path of the previous firmware (gn_unwrap.c, forwarded
+# as link opcode V2X_RX) so unsigned and non-demo-signed traffic still reaches the phone, the
+# unsigned transmit path of the previous firmware (geonet.c), and BLE pausing while USB is in use.
+# See NOTES.md.
+#
+# ESP-IDF 6.0.2 exactly: the C5 radio's private Wi-Fi driver ABI (otm_tx_custom.c) is pinned to it
+# by vanetza-idf's radio_c5.cmake and has only been validated there. The previous C firmware was
+# built with IDF 6.1; see FLASHING.md for the export script of each.
+#
+# vanetza-idf is taken from the colleague's tree rather than vendored (it is ~90 MB). Override with
+# -DVANETZA_IDF_DIR=... if it lives elsewhere.
+if(NOT VANETZA_IDF_DIR)
+    set(VANETZA_IDF_DIR "${CMAKE_CURRENT_LIST_DIR}/../microbu-esp32c5/external/vanetza-idf")
+endif()
+if(NOT EXISTS "${VANETZA_IDF_DIR}/idf_component.yml")
+    message(FATAL_ERROR "vanetza-idf not found at ${VANETZA_IDF_DIR}: clone microbu-esp32c5 beside this "
+                        "repository or pass -DVANETZA_IDF_DIR=<path to external/vanetza-idf>")
+endif()
+
+# Provenance guard for main/otm_tx_custom.c, copied unchanged from microbu-esp32c5/firmware/CMakeLists.txt:
+# this checked-in copy is what microbu::C5Radio::request() links against for every transmission.
+# Fail configure if either the pinned upstream or this file drifts from the reviewed revision.
+set(_otm_upstream "${VANETZA_IDF_DIR}/ports/esp_idf/third_party/otm/main/tx_custom.c")
+if(EXISTS "${_otm_upstream}")
+    file(READ "${_otm_upstream}" _otm_upstream_text)
+    string(REPLACE "\r\n" "\n" _otm_upstream_text "${_otm_upstream_text}")
+    string(SHA256 _otm_upstream_hash "${_otm_upstream_text}")
+    if(NOT _otm_upstream_hash STREQUAL "cb1dccfef96912ca59275e8a9102f41f56925b94a19d4a4629082aaeb779be1b")
+        message(FATAL_ERROR "OpenTrafficMap upstream tx_custom.c differs from the reviewed source revision (674e3412) -- review before updating main/otm_tx_custom.c and this hash")
+    endif()
+endif()
+set(_otm_checked_in "${CMAKE_CURRENT_LIST_DIR}/main/otm_tx_custom.c")
+file(READ "${_otm_checked_in}" _otm_checked_in_text)
+string(REPLACE "\r\n" "\n" _otm_checked_in_text "${_otm_checked_in_text}")
+string(SHA256 _otm_checked_in_hash "${_otm_checked_in_text}")
+if(NOT _otm_checked_in_hash STREQUAL "114693af99ce3866cfc767066d484e45822eaf15335d94a03626b60ac5777277")
+    message(FATAL_ERROR "main/otm_tx_custom.c differs from the reviewed copy -- review the change, then update this hash")
+endif()
+
+list(APPEND EXTRA_COMPONENT_DIRS "${VANETZA_IDF_DIR}")
+set(SDKCONFIG_DEFAULTS "${CMAKE_CURRENT_LIST_DIR}/sdkconfig.defaults")
+set(COMPONENTS main)
 include($ENV{IDF_PATH}/tools/cmake/project.cmake)
-
-# No longer need -Wl,-zmuldefs here - that was only for main/wifi_patches.c's
-# symbol-override attempt (which didn't work anyway; see docs/04-transmit-setup.md),
-# and that file is no longer part of the build. Superseded by main/tx_custom.c,
-# which bypasses the gate at a different layer instead of trying to override it.
-
 project(obu_firmware)
+add_compile_options(-Wno-error -Wno-cpp -Wno-error=implicit-function-declaration)
+idf_component_get_property(vanetza_lib vanetza-idf COMPONENT_LIB)
+if(vanetza_lib)
+    target_compile_options(${vanetza_lib} PRIVATE -Wno-error=implicit-function-declaration -Wno-error=cpp)
+endif()
+# GCC 15's stricter -Warray-bounds false-positives on NimBLE's fixed-size bond-store arrays
+# (upstream Apache Mynewt code); demote to a warning so the component still builds.
+idf_component_get_property(bt_lib bt COMPONENT_LIB)
+if(bt_lib)
+    target_compile_options(${bt_lib} PRIVATE -Wno-error=array-bounds)
+endif()