Low-power reference design central application

1 - overview

Please see the section overview of the peripheral application readme for the common description lowpower_peripheral

The low-power central reference design application is based on the temperature collector example that acts as a GAP central. In addition, it has the low-power feature enabled and optimized. The user can easily configure features such as Bluetooth scanning parameters, and other parameters related to the application, so that they can customize the application according to their eventual needs.

2 - Features

The low-power Central reference design application provides the following low-power features:

  • Application core in Deep Sleep mode during scan and connection with selective RAM retention.

  • Wake-up from Low Power mode with wake-up source such as Radio, Low-power timers, and IO.

The lp central application supports a Shell to output information from the device on LPUART interface. However, the shell is not source of wake-up when in Low-Power modes.

The Low-power reference design peripheral application supports up to 8 simultaneous connections: 7 lp central and one smartphone, or 8 lp central devices. However, the temperature service only supports one subscriber at a time.

By default, the first connected device is subscribed to temperature service and battery service. Only then, the other devices are subscribed to the battery service. The Low power central reference design is improved to also support battery notifications. Now, Low power central reference design also looks for battery service, enables its notifications and gets notified. It makes it not only a temperature_collector clone, as it can read battery level of the peripheral. No tweaking is needed, this feature is available by default.

3 - Running the low-power central reference design application

Supported boards:

  • KW45B41Z-EVK

  • K32W148-EVK

  • FRDM-MCXW71

  • KW47-EVK

  • MCX-W72-EVK

Features/Use cases

The application behavior is as follows:

At POR, start scanning immediately, scanning stops in the following cases:

  • On SW2 button press. When scanning is stopped, the device enters the Low Power mode.

  • On 30 sec timer expiration, then goes to Deep Sleep mode.

  • On connection establishment.

It establishes automatically a connection with a low-power reference design application (lp refdes app) or a temperature sensor by checking the temperature sensor service’s UUID in the advertising message and retrieves the temperature value. Note that Low Power Reference Design disconnects immediately after temperature is received.

On disconnect, the Application core and radio core go to Deep Sleep mode with full RAM retention. If gAppRestartScanAfterConnect is set to 1, the radio core restarts the scan activity. Application core still goes to Deep Sleep mode between messages from CM3. SW2 button has no effect.

Shell over LPUART peripheral outputs scanning, connection information, and temperature value.

3.1 - Application configuration

Details on the Application configuration parameters are directly described in the app_preinclude.h file of the project.

Some highlights on the parameters in app_preinclude.h that can be changed for this application are given here:

  • gDebugConsoleEnable_d to 1: Enables PRINTF.

  • gAppUseBonding_d and gAppUsePairing_d to 0: Must be aligned to the same configuration as the peripheral device.

  • gAppUsePrivacy_d to 0: must be aligned with the peripheral device.

  • gAppExtAdvEnable_d to 1: enables the capability to scan and print scanned Extended Advertisements (requires OPT host lib).

  • gAppRestartScanAfterConnect to 1: when connection ends, the device switches back to Scan mode.

  • gPLATFORM_DisableNbuLowpower_d to 1: prevents Radio domain to go to Low Power mode.

  • gAppLowpowerEnabled_d to 0: disables Low Power (for sanity test without low power).

3.2 - Expected data output on console

Copyright  2024  NXP

BLE Lowpower Central>
trying to connect to a lowpower peripheral refdes application
Short press SW2 to start/stop scanning
Short press SW3 to enable/disable low power
Long press SW3 to print a message

Scanning...

Scanning stopped!

Going into lowpower (RAMOFF)

Shen connected to a low power peripheral reference design application, following output should be displayed:

Copyright  2024  NXP

BLE Lowpower Central>
trying to connect to a lowpower peripheral refdes application
Short press SW2 to start/stop scanning
Short press SW3 to enable/disable low power
Long press SW3 to print a message

Scanning...

Found device:
NXP_TEMP
00:60:37:96:BE:12
Scanning stopped!

Connected!
Temperature: 24 C
Battery: 100 %

Disconnected!

Going into lowpower (RAMOFF)

Notes :

  • When plugging the USB cable to power ON the board, you may miss the first characters until your terminal is fully connected to your device. Press power ON reset button to have full display.

  • When paired and bounded, the message paired will no longer be displayed. You may see Privacy’s ready instead.