STM32WB BLE MESH Sensor Model

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1. STM32WB - Fast Firmware Update Over The Air

This is a description how to improve the data throughput while updating the STM32WB Application or Wireless Stack thanks to wireless STM32WB BLE protocol. The current implementation of "BLE_ota" application is described with the following Application Note:

AN-5247- Over-the-air application and wireless firmware update for STM32WB Series microcontrollers

1.1. Limitation with current implementation

The OTA RAW Data Characteristic is limited to 20 bytes
So ATT Packet data transmitted is limited.

The following figure is an air capture of the raw data characteristic sent by the ST BLE Sensor application

ATT Write - 20 bytes
File:OTA Raw data characteristic - 20 bytes.png

1.2. How to increase the data throughput

by increasing the size of the OTA RAW data characteristic to 248 - done with CubeWB 1.12.0 release

#define OTAS_STM_RAW_DATA_SIZE    (248)                                                //otas_stm.h
#define OTA_RAW_DATA_CHAR_SIZE    OTAS_STM_RAW_DATA_SIZE      //otas_stm.c

 /**
   *  Add Raw Data Characteristic
   */
  aci_gatt_add_char(OTAS_Context.OTAS_SvcHdle,
                    OTA_UUID_LENGTH,
                    (Char_UUID_t *)OTA_RAW_DATA_CHAR_UUID,
                    OTA_RAW_DATA_CHAR_SIZE,
                    CHAR_PROP_WRITE_WITHOUT_RESP,
                    ATTR_PERMISSION_NONE,
                    GATT_NOTIFY_ATTRIBUTE_WRITE | GATT_NOTIFY_WRITE_REQ_AND_WAIT_FOR_APPL_RESP,
                    10,
                    1,
                    &(OTAS_Context.OTAS_Raw_Data_CharHdle));

by increasing the size of ATT Maximum Transmission Unit (MTU) which is the maximum length of an ATT packet

/**
 * Maximum supported ATT_MTU size
 * This parameter is ignored by the CPU2 when CFG_BLE_OPTIONS is set to 1"
 */
#define CFG_BLE_MAX_ATT_MTU             (251)

by managing with GATT Client remote application the negotiation of the ATT MTU to increase the data payload for the transmitted packets

ATT MTU Exchange
File:ATT MTU Exchange.png

1.3. ANDROID - ST BLE Sensor v4.12.0 - How to

The version v4.12.0 is available on Google Play https://play.google.com/store/apps/details?id=com.st.bluems&hl=en&gl=US