Reduce IMU BLE payloads in firmware 2.3.0

[TobiasRoeddiger]

Reduce IMU BLE samples from 36 to 24 bytes: recover the six original int16 accelerometer/gyroscope counts and retain all three calibrated magnetometer floats. The 2.3.x library restores the exact existing float32 values and units. Nine samples fit in one 244-byte notification, up from six.

Acquisition, timestamps, parsing metadata, SD recording, and .oe files keep their existing formats. Encoding rejects values that cannot be reconstructed losslessly. Depends on OpenEarable/protocol#3; stacked on #355 so the firmware version changes with the transport.

Validation: FOTA build passes; seven transport tests pass, including all 65,536 signed counts, unchanged input/SD bytes, batch boundaries and invalid values. Hardware release validation will follow integration.

[github-actions]

✅ Unit tests passed

4 passed, 0 failed/error, 0 skipped — view workflow run

Test scenario	Platform	Result
openearable.unit.sensor_component	native_sim/native/64	✅ passed
openearable.unit.sensor_transport	native_sim/native/64	✅ passed
openearable.unit.ring_buffer	native_sim/native/64	✅ passed
openearable.unit.audio_startup	native_sim/native/64	✅ passed

Download the unit-test-results artifact for full Twister reports and logs.

[github-actions]

Compiler warnings

The extended-warning build completed successfully.

Application compiler warnings

Show warnings

unicast_server/main.cpp:78:33: warning: 'int usb_enable(usb_dc_status_callback)' is deprecated [-Wdeprecated-declarations]
src/SensorManager/Baro.cpp:93:34: warning: implicit conversion from 'float' to 'double' to match other operand of binary expression [-Wdouble-promotion]

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[github-actions]

Build output available:
openearable_v2_firmware.zip
openearable_v2_fota.zip

[github-actions]

CodeChecker static analysis (advisory)

Note

This report is informational. It does not block merging and does not change code.

At a glance

Scope	Result
Findings on lines changed by this PR	0
Findings in the complete codebase	8
Analyzer invocations completed	180
Analyzer invocations failed	0

Findings on changed lines

No non-style findings were reported on lines changed by this PR.

Analyzer coverage

Analyzer	Completed	Failed
clangsa	90	0
cppcheck	90	0

Complete-codebase summary

Severity: 2 high, 6 low
Reported by analyzer: clangsa: 8

Complete-codebase findings

Each finding includes source context. The > line and carets identify the expression reported by the analyzer.

Show detailed findings with source context (8 of 8)

HIGH — src/audio/audio_datapath.c:1002 — Null pointer passed as 1st argument to memory set function

  1001 | 
> 1002 |             memset(tx_buf, 0, BLK_MULTI_CHAN_SIZE_OCTETS);
       |                    ^^^^^^
  1003 |         }

HIGH — src/audio/sw_codec_select.c:220 — Assigned value is garbage or undefined

  219 | 
> 220 |         meta_out->bytes_per_location = bytes_written;
      |                                        ^^^^^^^^^^^^^
  221 |         meta_out->locations &= meta_in->locations;

LOW — src/audio/audio_system.c:238 — Value stored to 'audio_q_num_used' is never read

  237 |         if (unlikely(++debug_trans_count >= DEBUG_INTERVAL_NUM)) {
> 238 |             audio_q_num_used = k_msgq_num_used_get(&audio_q_in);
      |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  239 |             LOG_DBG(COLOR_CYAN "IN filled: %d" COLOR_RESET, audio_q_num_used);

LOW — src/audio/audio_system.c:745 — Value stored to 'num_ch' during its initialization is never read

  744 | 
> 745 |     int num_ch = POPCOUNT(locations);
      |         ^^^^^^
  746 | 

LOW — src/audio/le_audio_rx.c:125 — Value stored to 'bad_frame_percentage' during its initialization is never read

  124 |                 rx_stats[location_index].bad_or_empty_frame_cnt;
> 125 |     double bad_frame_percentage =
      |            ^^^^^^^^^^^^^^^^^^^^
  126 |         (total_frames > 0) ? (((double)rx_stats[location_index].bad_or_empty_frame_cnt /

LOW — src/audio/le_audio_rx.c:160 — Value stored to 'ret' is never read

  159 |         /* FIFO buffer is full, swap out oldest frame for a new one */
> 160 |         ret = k_msgq_get(&ble_q_rx, (void *)&stale_buf, K_NO_WAIT);
      |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  161 |         /* Checking return value of k_msgq_get() is not necessary here,

LOW — src/bluetooth/bt_management/scanning/bt_mgmt_scan.c:58 — Value stored to 'scan_param' during its initialization is never read

  57 | 
> 58 |     struct bt_le_scan_param *scan_param =
     |                              ^^^^^^^^^^
  59 |         BT_LE_SCAN_PARAM(NRF_AUDIO_GATEWAY_SCAN_TYPE, BT_LE_SCAN_OPT_FILTER_DUPLICATE,

LOW — src/modules/audio_sync_timer.c:138 — Value stored to 'cc_get_calls' is never read

  137 | 
> 138 |     cc_get_calls = 0;
      |                    ^
  139 | 

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