Low-power reference design peripheral application

1 - overview

Two low-power reference design applications are provided in the reference_design folder:

  • Low power peripheral application demonstrating the low power feature on an advertiser peripheral Bluetooth LE device.

  • Low power central application demonstrating the low power feature on a scanner central Bluetooth LE device. Refer to the readme of refernce design central application lowpower_central

These applications aim at providing:

  • reference code for low power/timing optimization on a Bluetooth Low Energy application. These can be used in first intent for porting a new application with low power functionality.

  • A way for measuring the power consumption, wake-up time, and active time in various low power modes. The default low-power mode used in different modes are shown as follows:

BLE state

App core

Radio core

Advertise mode

Deep sleep mode

Deep sleep mode

Connected mode

Deep Sleep mode

Deep Sleep mode

Scanning mode

Deep Sleep mode

WFI or Deep Sleep mode

No BLE activity

Deep power down mode

Deep power down mode

Running the demo

Toolchain supported

  • IAR Embedded Workbench (IDE version details are in the Release Notes)

  • MCUXpresso IDE (IDE version details are in the Release Notes)

  • GCC ARM Embedded (IDE version details are in the Release Notes)

Hardware requirements

  • Type-C USB cable

  • KW47-EVK Board

  • Personal Computer

Prepare the demo:

  1. Connect the USB cable between the PC host and the OpenSDA USB port on the board.

  2. Download the program to the target board.

  3. Download the NBU firmware to the target board. See the Release Note about details

  4. Open a serial terminal application and use the following settings with the detected serial device:

    • 115200 baud rate

    • 8 data bits

    • No parity

    • One stop bit

    • No flow control

  5. Eventually, press the reset button on your board to restart the demo.

Supported boards:

  • KW45B41Z-EVK

  • K32W148-EVK

  • FRDM-MCXW71

  • KW47-EVK

  • MCX-W72-EVK

Features/Use cases

The low-power peripheral reference design application is based on the temperature sensor example and has all Bluetooth services that the temperature sensor offers. In addition, it has the low-power feature enabled and optimized. The user can easily configure features such as Bluetooth advertising parameters, and other parameters related to the application, so that they can customize the application according to their eventual needs.

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

  • Low-power modes in advertising and connected modes: Application core goes to Deep Sleep and wakes up only when the radio core sends a message to the host stack. The radio core goes to Deep Sleep between each Bluetooth LE event.

  • Wake-up from Low Power modes with wake-up sources such as Radio, Low-power timers, and IOs.

  • In ble_conn_manager.h file, the user can set the preferred LE PHY setting (1M/2M/Coded) with the definition of gConnDefaultTxPhySettings_c, gConnDefaultRxPhySettings_c, and gConnInitiatePhyUpdateRequest_c.

  • ADV in various configurations:

    • Connectable / not connectable,

    • ADV payload, Scan Response Payload,

    • Extended ADV

2 - Implemented Bluetooth LE profiles and services

The low-power reference design peripheral application is based on the Temperature Sensor application. It implements a GATT server, a custom profile, and the following services.

  • Temperature Service (UUID: 01ff0200-ba5e-f4ee-5ca1-eb1e5e4b1ce0)

  • Battery Service v1.0

  • Device Information Service v1.1

The application behaves as a GAP peripheral node. It enters GAP General Discoverable Mode and waits for a GAP central node to connect and configure notifications for the temperature value.

The Temperature service is a custom service that implements the Temperature characteristic (UUID: 0x2A6E) with a Characteristic Presentation Format descriptor (UUID: 0x2904), both defined by the Bluetooth SIG.

The default advertisement message is the same as the temperature sensor demo:

Length

Type

Value

2

x01(AdFlag)

0x06

17

0x07(AdComplete128bitServiceList)

0xE01C4B5E1EEBA15CEEF45EBA0002FF01

9

0x08(AdShortenedLocalName)

0x4E58505F54454D50

The scan response is empty by default. The advertisement message length is 2+17+9+3 (number of bytes for “length” information) = 31 bytes.

The advertising interval is set to 500 ms by default, it advertises on all 3 ADV channels. and it is connectable. Users can establish a connection with the device by using either another KW45 board programmed with a low-power central device, “temperature_collector” demo, or with a smartphone compatible with Bluetooth 4.2 or above.

3 - Running the low-power reference design peripheral application

Once the Kinetis device is programmed with the low-power reference design demo project, and after a power cycle, it starts to advertise every 500 ms as soon as the hardware and software initializations are completed. This allows users to measure the start-up time from Power-On-Reset to the first TX. The power consumption for one advertising event, as well as the current between two advertising events can also be measured. The same applies to the case when the device is connected to another Bluetooth central device where it allows the measurement of the power consumption of the connection event.

A low-power timer of 30 seconds is set at the beginning of advertising, so the device stops advertising when this timer expires. The user can also stop the advertisement by pressing the button SW2. When advertising stops, the user can easily perform power consumption measurement of the state where the main domain is in Deep Power Down mode and the Radio domain is also in this mode.

The MCU stays in this mode until the wake-up from one of the wake up sources. By default, the wake up sources are WUU pins (including the SW2 button). At wake-up, the device starts to advertise immediately, just like waking up from a Power-On-Reset. This allows the user to measure the wake-up time.

The low-power reference design freertos application by default will wake up from lowpower 8 seconds after stopping any activity to demonstrate the tickless mode feature. You can adjust the timeout with the gAppTaskWaitTimeout_ms_c flag in the app_preinclude.h file, its value in our demo is 8000ms. If this flag is not defined in the application its value will be osaWaitForever_c and there will be no OS wake up.

The graph below illustrates the default behavior of the low-power reference design application:

The user can connect to the device anytime when this last is in advertising state. The connection automatically disconnects when the temperature value is sent to the peer device, or after 10 seconds timer (started from connection establishment).

3.1 - Software configurations

To make the power measurement simpler for different use cases and hardware configurations, the low-power reference design offers options to configure the EVK board and the application.

3.2 - Application configuration

The Low Power service is initialized in app_services_init(). By default, both domains enter Deep Sleep mode whenever it is possible.

New APIs at application level are introduced to simplify the usage of the low power module:

    1. BleApp_SetLowPowerModeConstraint: The developer sets its parameter according to its state: gAppLowPowerConstraintInAdvertising_c, gAppLowPowerConstraintInConnected_c or gAppLowPowerConstraintInNoBleActivity_c, and the Low Power manager automatically enters the suitable Low Power mode.

    1. BleApp_ReleaseLowPowerModeConstraint: When the constraints change and the application needs to go to a different Low Power mode, this API is called to release the previous constraints.

The application configuration parameters are directly described in the app_preinclude.h file in the project. Some highlights on the parameters available:

  • gAppExtAdvEnable_d to 1: enables the capability to perform extended advertising event (requires OPT host lib).

  • gAppRestartAdvAfterConnect to 1: when connection ends, the device restarts advertising mode. The device goes in deep sleep mode between advertising intervals.

  • gPlatformDcdcBuckMode_d: allows to disable the DCDC if it is set to 0 (requires HW changes).

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

3.3 - Expected data output on console

Connect with a Lowpower Central or Temperature collector device
Short press SW2 to start/stop advertising
Short press SW3 to enable/disable low power
Long press SW3 to print a message

Advertising...

Advertising stopped

Wake up from RAMOFF

Advertising...

When connected to a low power central reference design application, the following output should be displayed:

Connect with a Lowpower Central or Temperature collector device
Short press SW2 to start/stop advertising
Short press SW3 to enable/disable low power
Long press SW3 to print a message

Advertising...
Connected
Paired
Temperature sent: 25 C
Battery level sent: 100%
Disconnected

Advertising...

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 to have full display.

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