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esp-idf/examples/bluetooth/nimble/blecent/README.md

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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.

A Python based utility blecent_test.py is also provided (which will run as a BLE GATT server) and can be used to test this example.

Note :

  • Make sure to run python -m pip install --user -r $IDF_PATH/requirements.txt -r $IDF_PATH/tools/ble/requirements.txt to install the dependency packages needed.
  • Currently this Python utility is only supported on Linux (BLE communication is via BLuez + DBus).

How to use example

Configure the project

idf.py menuconfig
  • Set serial port under Serial Flasher Options.

Build and Flash

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

idf.py -p PORT 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

This is the 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

This is the 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

Running Python Utility

python blecent_test.py

Python Utility Output

This is this output seen on the python side on successful connection:

discovering adapter...
bluetooth adapter discovered
powering on adapter...
bluetooth adapter powered on
Advertising started
GATT Data created
GATT Application registered
Advertising data created
Advertisement registered
Read Request received
 	SupportedNewAlertCategoryCharacteristic
	Value: 	 [dbus.Byte(2)]
Write Request received
 	AlertNotificationControlPointCharacteristic
	Current value: 	 [dbus.Byte(0)]
	New value: 	 [dbus.Byte(99), dbus.Byte(100)]

Notify Started
New value on write: 	 [dbus.Byte(1), dbus.Byte(0)]
	Value on read: 	 [dbus.Byte(1), dbus.Byte(0)]

Notify Stopped

exiting from test...
GATT Data removed
GATT Application unregistered
Advertising data removed
Advertisement unregistered
Stop Advertising status:  True
disconnecting device...
device disconnected
powering off adapter...
bluetooth adapter powered off
Service discovery passed
	Service Discovery Status: 0
Read passed
	SupportedNewAlertCategoryCharacteristic
	Read Status: 0
Write passed
	AlertNotificationControlPointCharacteristic
	Write Status: 0
Subscribe passed
	ClientCharacteristicConfigurationDescriptor
	Subscribe Status: 0