Skip to main content
BlueBus provides full hands-free telephony capabilities by integrating with your BMW’s factory telephone controls and emulating the original BMW phone system on the I-Bus.

​
Hands-Free Profile (HFP)

The Bluetooth module implements the Hands-Free Profile to enable calling features.

​
HFP features

  • Answer and end calls via vehicle controls
  • Caller ID display on all supported screens
  • Outgoing call support with number entry
  • Redial last number
  • Voice recognition (Siri/Google Assistant)
  • Microphone integration with factory telephone microphone
You can enable or disable HFP through the vehicle’s configuration menu (CONFIG_SETTING_HFP). When enabled, BlueBus establishes both A2DP and HFP profiles with your phone (firmware/application/lib/bt.c:183).

​
Call control

​
Answering calls

Incoming calls can be answered using:
  • Telephone button on BMBT (Board Monitor)
  • Telephone button on MID (Multi-Information Display)
  • Steering wheel telephone button (MFL)
The BTCommandCallAccept function (firmware/application/lib/bt.c:72) sends the appropriate command to the Bluetooth module (BM83_CMD_MMI_ACTION_ACCEPT_CALL).

​
Ending calls

Active calls can be terminated using:
  • Same telephone controls used to answer
  • BTCommandCallEnd function sends BM83_CMD_MMI_ACTION_END_CALL

​
Making calls

You can initiate calls through several methods:1. Dial from phonebook
  • Access downloaded contacts via PBAP
  • Select contact and dial
2. Manual number entry
  • Enter number using vehicle’s input controls
  • Cleaned and validated per ITU-T V.250 standard
  • Supports +, comma (,), #, *, digits 0-9, and A-C
3. Redial last number
  • Quick access via redial function
  • Uses phone’s last dialed number memory
The BTCommandDial function (firmware/application/lib/bt.c:110) handles number validation and sends properly formatted dial commands.

​
Redial functionality

The redial feature uses the phone’s native last number redial: 
BTCommandRedial(bt)  // firmware/application/lib/bt.c:150
This sends either the BC127 AT+BLDN command or the BM83 redial command depending on your Bluetooth module variant.

​
Caller ID display

Incoming and outgoing call information is displayed on your vehicle’s screen.

​
Caller ID information

  • Phone number for unknown callers
  • Contact name from phone’s contact list
  • Call status indicators
The caller ID is stored in the bt.callerId field (BT_CALLER_ID_FIELD_SIZE) and displayed using telephone UI commands.

​
Display formats

BMBT (Board Monitor):
  • Full graphical telephone interface
  • Caller name and number
  • On-call indicators (IBUS_TEL_CHAR_ON_CALL_LEFT, IBUS_TEL_CHAR_ON_CALL_RIGHT)
  • Handsfree icon (IBUS_TEL_CHAR_HANDSFREE_ICON)
MID (Multi-Information Display):
  • Caller information on single line display
  • Scrolling for long names/numbers
IKE (Instrument Cluster):
  • Basic caller information on check control display
  • Call status notifications

​
Telephone LED control

BlueBus controls the factory telephone LED to indicate system status:
LED StateMeaning
RedBluetooth device disconnected
GreenDevice connected and ready
Green BlinkingIncoming call
YellowCall in progress
LED control uses IBUS_TEL_CMD_LED_STATUS (0x2B) with states defined in firmware/application/lib/ibus.h:424-431.

​
Voice recognition

Activate your phone’s voice assistant (Siri or Google Assistant) using the vehicle’s voice button.

​
Activation

  • Press and hold the voice/telephone button on the steering wheel
  • BTCommandToggleVoiceRecognition (firmware/application/lib/bt.c:624) sends the command
  • Voice recognition status tracked: BT_VOICE_RECOG_ON / BT_VOICE_RECOG_OFF
When voice recognition is active, the caller ID field displays “Voice Assistant” and the system enters voice recognition mode for audio routing.

​
Microphone configuration

BlueBus uses your vehicle’s factory telephone microphone with configurable gain settings.

​
Microphone settings

Gain control:
  • Adjustable gain levels (CONFIG_SETTING_MIC_GAIN)
  • Preamp settings (CONFIG_SETTING_MIC_PREAMP)
  • Bias voltage (CONFIG_SETTING_MIC_BIAS)
Gain adjustment:
  • BM83CommandMicGainUp / BM83CommandMicGainDown functions
  • Multiple gain levels in BTBM83MicGainTable
  • Stored in EEPROM for persistence

​
Audio routing

During calls, audio is routed through:
  • Input: Factory telephone microphone
  • Output: Vehicle speakers (with volume control)
  • Mode: SCO (Synchronous Connection-Oriented) link for voice
The bt.scoStatus field tracks SCO connection state (BT_CALL_SCO_CLOSE / BT_CALL_SCO_OPEN).

​
Telephone modes

BlueBus supports multiple telephone operation modes:

​
Available modes

Default mode (CONFIG_SETTING_TEL_MODE_DEFAULT):
  • Standard HFP operation
  • Audio muting during calls
  • Full integration with vehicle systems
TCU mode (CONFIG_SETTING_TEL_MODE_TCU):
  • Emulates BMW Assist TCU module
  • Compatible with factory TCU wiring
  • Special volume handling
No-mute mode (CONFIG_SETTING_TEL_MODE_NO_MUTE):
  • Disables automatic audio muting
  • For custom audio setups
Analog mode (CONFIG_SETTING_TEL_MODE_ANALOG):
  • Direct analog audio path
  • Bypasses digital processing

​
Volume control

Telephone audio volume is independently adjustable:
  • Separate volume setting from music audio
  • Volume offset configuration (CONFIG_SETTING_TEL_VOL)
  • Offset range: 0 to CONFIG_SETTING_TEL_VOL_OFFSET_MAX (0x0F)
  • TCU mode volume (CONFIG_SETTING_DAC_TEL_TCU_MODE_VOL)

​
Call status tracking

The system tracks detailed call states: 
// Call status values (firmware/application/lib/bt.h:33)
BT_CALL_INACTIVE      // No active call
BT_CALL_INCOMING      // Ringing
BT_CALL_OUTGOING      // Dialing
BT_CALL_ACTIVE        // Connected call
Call status from BM83 module (firmware/application/lib/bt/bt_bm83.h:254-260):
  • BM83_DATA_CALL_STATUS_IDLE
  • BM83_DATA_CALL_STATUS_VR (voice recognition)
  • BM83_DATA_CALL_STATUS_INCOMING
  • BM83_DATA_CALL_STATUS_OUTGOING
  • BM83_DATA_CALL_STATUS_ACTIVE
  • BM83_DATA_CALL_STATUS_ACTIVE_CALL_WAITING
  • BM83_DATA_CALL_STATUS_ACTIVE_CALL_HOLD

​
Phonebook access (PBAP)

BlueBus can download contacts from your phone using the Phone Book Access Profile.

​
PBAP features

  • Download contacts from phone memory
  • Access call history (incoming, outgoing, missed calls)
  • Support for favorites and speed dial
  • Multiple phonebook objects supported

​
Phonebook objects

The BTCommandPBAPGetPhonebook function (firmware/application/lib/bt.c:334) supports:
  • BT_PBAP_OBJ_PHONEBOOK - Main contact list
  • BT_PBAP_OBJ_INCOMING - Incoming call history
  • BT_PBAP_OBJ_OUTGOING - Outgoing call history
  • BT_PBAP_OBJ_MISSED - Missed calls
  • BT_PBAP_OBJ_COMBINED - Combined call history
  • BT_PBAP_OBJ_SPEEDDIAL - Speed dial entries
  • BT_PBAP_OBJ_FAVORITES - Favorite contacts
PBAP session management includes open (BTCommandPBAPOpen), close (BTCommandPBAPClose), and abort (BTCommandPBAPAbort) functions for reliable phonebook access.

Build docs developers (and LLMs) love

Get started for freeTalk to us