BLE central example

(See the README.md file in the upper level 'examples' directory for more information about examples.)

This example creates GATT client and performs passive scan, it then connects to peripheral device if the device advertises connectability and the device advertises support for the Alert Notification service (0x1811) as primary service UUID.

It performs three GATT operations against the specified peer:

• Reads the ANS Supported New Alert Category characteristic.

• After the read operation is completed, writes the ANS Alert Notification Control Point characteristic.

• After the write operation is completed, subscribes to notifications for the ANS Unread Alert Status characteristic.

If the peer does not support a required service, characteristic, or descriptor, then the peer lied when it claimed support for the alert notification service! When this happens, or if a GATT procedure fails, this function immediately terminates the connection.

It uses ESP32's Bluetooth controller and NimBLE stack based BLE host.

This example aims at understanding BLE service discovery, connection and characteristic operations.

To test this demo, use any BLE GATT server app that advertises support for the Alert Notification service (0x1811) and includes it in the GATT database.

How to use example

Configure the project

make menuconfig

• Set serial port under Serial Flasher Options.

• Select 'Enable NimBLE host stack' under 'Component config > Bluetooth'.

Build and Flash

Build the project and flash it to the board, then run monitor tool to view serial output:

make -j4 flash monitor

(To exit the serial monitor, type Ctrl-].)

See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.

Example Output

There is this console output on successful connection:

I (202) BTDM_INIT: BT controller compile version [0b60040]
I (202) system_api: Base MAC address is not set, read default base MAC address from BLK0 of EFUSE
W (212) phy_init: failed to load RF calibration data (0xffffffff), falling back to full calibration
I (422) phy: phy_version: 4007, 9c6b43b, Jan 11 2019, 16:45:07, 0, 2
I (722) NimBLE_BLE_CENT: BLE Host Task Started
GAP procedure initiated: stop advertising.
GAP procedure initiated: discovery; own_addr_type=0 filter_policy=0 passive=1 limited=0 filter_duplicates=1 duration=forever
GAP procedure initiated: connect; peer_addr_type=1 peer_addr=xx:xx:xx:xx:xx:xx scan_itvl=16 scan_window=16 itvl_min=24 itvl_max=40 latency=0 supervision_timeout=256 min_ce_len=16 max_ce_len=768 own_addr_type=0
Connection established
GATT procedure initiated: discover all services
GATT procedure initiated: discover all characteristics; start_handle=1 end_handle=3
GATT procedure initiated: discover all characteristics; start_handle=20 end_handle=26
GATT procedure initiated: discover all characteristics; start_handle=40 end_handle=65535
GATT procedure initiated: discover all descriptors; chr_val_handle=42 end_handle=43
GATT procedure initiated: discover all descriptors; chr_val_handle=49 end_handle=65535
Service discovery complete; status=0 conn_handle=0
GATT procedure initiated: read; att_handle=45
GATT procedure initiated: write; att_handle=47 len=2
GATT procedure initiated: write; att_handle=43 len=2
Read complete; status=0 conn_handle=0 attr_handle=45 value=0x02
Write complete; status=0 conn_handle=0 attr_handle=47
Subscribe complete; status=0 conn_handle=0 attr_handle=43

There is this console output on failure (or peripheral does not support New Alert Service category):

I (180) BTDM_INIT: BT controller compile version [8e87ec7]
I (180) system_api: Base MAC address is not set, read default base MAC address from BLK0 of EFUSE
I (250) phy: phy_version: 4000, b6198fa, Sep  3 2018, 15:11:06, 0, 0
I (480) NimBLE_BLE_CENT: BLE Host Task Started
GAP procedure initiated: stop advertising.
GAP procedure initiated: discovery; own_addr_type=0 filter_policy=0 passive=1 limited=0 filter_duplicates=1 duration=forever
GAP procedure initiated: connect; peer_addr_type=1 peer_addr=xx:xx:xx:xx:xx:xx scan_itvl=16 scan_window=16 itvl_min=24 itvl_max=40 latency=0 supervision_timeout=256 min_ce_len=16 max_ce_len=768 own_addr_type=0
Connection established
GATT procedure initiated: discover all services
GATT procedure initiated: discover all characteristics; start_handle=1 end_handle=3
GATT procedure initiated: discover all characteristics; start_handle=20 end_handle=26
GATT procedure initiated: discover all characteristics; start_handle=40 end_handle=65535
GATT procedure initiated: discover all descriptors; chr_val_handle=42 end_handle=43
GATT procedure initiated: discover all descriptors; chr_val_handle=47 end_handle=65535
Service discovery complete; status=0 conn_handle=0
Error: Peer doesn't support the Supported New Alert Category characteristic
GAP procedure initiated: terminate connection; conn_handle=0 hci_reason=19
disconnect; reason=534