Power Management

All power-managment functionality is handled by the TI power driver and are used by the peripheral drivers (e.g. UART, SPI, I2C, etc..). Applications can prevent, if they choose, the CC13xx or CC26xx from entering low power modes by setting a power constraint.

By default, all the examples in SimpleLink CC13xx/CC26xx SDK will put the CC13xx or CC26xx in standby mode if there is no task running. This is achieved by configuring the TI power driver and the kernel to do so, as shown in the following step.

  1. In the FreeRTOSConfig.h, set following define:

    Listing 26. FreeRTOS Kernel Power Management Configuration
    #define configUSE_TICKLESS_IDLE         1

    This means we use a built-in FreeRTOS functionality to get the number of ticks until the next tasks need to be executed. Please refer to FreeRTOS Low Power Support. for more information.

  2. When there is no task running within 2 ticks from the future, then the vPortSuppressTicksAndSleep(TickType_t xExpectedIdleTime) will be called, which returns the number of ticks until next task occurs. The function can be found in {SDK_INSTALL_DIR}\kernel\freertos\dpl\PowerCCxxxx_freertos.c

  3. In vPortSuppressTicksAndSleep, we can see the tick is saved to a global variable and Power_idleFunc() gets called.

    Listing 27. PowerCCxxxx_freertos.c:: vPortSuppressTicksAndSleep
     1void vPortSuppressTicksAndSleep(TickType_t xExpectedIdleTime)
 2{
 3    /* Stash FreeRTOS' expected idle time */
 4    PowerCCxxxx_idleTimeOS = xExpectedIdleTime;
 5
 6    /*
 7     * call Power-driver-specified idle function, to conditionally invoke the
 8     * Power policy
 9     */
10    Power_idleFunc();
11}

  4. Power_idleFunc takes in policyFxn and policyFxn is defined using SysConfig tool Figure 64.. By default, TI sets the PowerCCxxxx_standbyPolicy as policyFxn. Power_idleFunc is defined in {SDK_INSTALL_DIR}\source\ti\drivers\power\PowerCCxxxx.c and PowerCCxxxx_standbyPolicy can be found in {SDK_INSTALL_DIR}\kernel\freertos\dpl\PowerCCxxxx_freetos.c

    ../_images/freertos_sysconfig_power_policy.png

    Figure 64. Configure Power Policy for Idle Function.

  5. In the sysconfig generated files, you will find the following example in ti_drivers_config.c.

    Listing 28. ti_drivers.c
    1const PowerCCXXXX_Config PowerCCxxxx_config = {
2      .policyInitFxn            = NULL,
3      .policyFxn                = PowerCCxxxx_standbyPolicy,
4};

With BLE5-Stack applications, the power contraint is set in main() by defining the POWER_SAVINGS preprocessor symbol. When defined, enabled, the device enters and exits sleep as required for BLE5-Stack events, peripheral events, application timers, and so forth. When undefined, the device stays in active mode.

Also see Measuring Bluetooth Smart Power Consumption for steps to analyze the system power consumption and battery life.