TI-RTOS Overview

TI-RTOS is the operating environment for BLE5-Stack projects on CC26x2 devices. The TI-RTOS kernel is a tailored version of the legacy SYS/BIOS kernel and operates as a real-time, preemptive, multi-threaded operating system with drivers, tools for synchronization and scheduling.

Threading Modules

The TI-RTOS kernel manages four distinct context levels of thread execution as shown in Figure 2. The list of thread modules are shown below in a descending order in terms of priority.

• A Hwi or Hardware interrupt
• A Swi or Software interrupt
• Tasks
• The Idle Task for background idle functions

Figure 2. TI-RTOS Execution Threads

This section describes these four execution threads and various structures used throughout the TI-RTOS for messaging and synchronization.

In most cases, the underlying TI-RTOS functions have been abstracted to higher-level functions in util.c (Util). The lower-level TI-RTOS functions are described in the TI-RTOS Kernel API Guide found here TI-RTOS Kernel User Guide. This document also defines the packages and modules included with the TI-RTOS.

Hardware Interrupts (Hwi)

Hwi threads (also called Interrupt Service Routines or ISRs) are the threads with the highest priority in a TI-RTOS application. Hwi threads are used to perform time critical tasks that are subject to hard deadlines. They are triggered in response to external asynchronous events (interrupts) that occur in the real-time environment. Hwi threads always run to completion but can be preempted temporarily by Hwi threads triggered by other interrupts, if enabled. Specific information on the nesting, vectoring, and functionality of interrupts can be found in the CC26x2 Technical Reference Manual.

Generally, interrupt service routines are kept short as not to affect the hard real-time system requirements. Also, as Hwis must run to completion, no blocking APIs may be called from within this context.

TI-RTOS drivers that require interrupts will initialize the required interrupts for the assigned peripheral.

Note

Debugging provides an example of using GPIOs and Hwis. While the SDK includes a peripheral driver library to abstract hardware register access, it is suggested to use the thread-safe TI-RTOS drivers.

The Hwi module for the CC26x2 also supports Zero-latency interrupts. These interrupts do not go through the TI-RTOS Hwi dispatcher and therefore are more responsive than standard interrupts, however this feature prohibits its interrupt service routine from invoking any TI-RTOS kernel APIs directly. It is up to the ISR to preserve its own context to prevent it from interfering with the kernel’s scheduler.

For the Bluetooth low energy protocol stack to meet RF time-critical requirements, all application-defined Hwis execute at the lowest priority. TI does not recommend modifying the default Hwi priority when adding new Hwis to the system. No application-defined critical sections should exist to prevent breaking TI-RTOS or time-critical sections of the Bluetooth low energy protocol stack. Code executing in a critical section prevents processing of real-time interrupt-related events.

Software Interrupts (Swi)

Patterned after hardware interrupts (Hwi), software interrupt threads provide additional priority levels between Hwi threads and Task threads. Unlike Hwis, which are triggered by hardware interrupts, Swis are triggered programmatically by calling certain Swi module APIs. Swis handle threads subject to time constraints that preclude them from being run as tasks, but whose deadlines are not as severe as those of hardware ISRs. Like Hwis, Swi threads always run to completion. Swis allow Hwis to defer less critical processing to a lower-priority thread, minimizing the time the CPU spends inside an interrupt service routine, where other Hwis can be disabled. Swis require only enough space to save the context for each Swi interrupt priority level, while Tasks use a separate stack for each thread.

Similar with Hwis, Swis should be kept to short and may not include any blocking API calls. This allows high priority tasks such as the wireless protocol stack to execute as needed. It is suggested to _post() some TI-RTOS synchronization primitive to allow for further post processing from within a Task context. See Figure 3. to illustrate such a use-case.

Figure 3. Preemption Scenario

The commonly used Clock module operates from within a Swi context. It is important that functions called by a Clock object do not invoke blocking APIs and are rather short in execution.

Task

Task threads have higher priority than the background (Idle) thread and lower priority than software interrupts. Tasks differ from software interrupts in that they can wait (block) during execution until necessary resources are available. Tasks require a separate stack for each thread. TI-RTOS provides a number of mechanisms that can be used for inter-task communication and synchronization. These include Semaphores, Event, Message queues, and Mailboxes.

Idle Task

Idle threads execute at the lowest priority in a TI-RTOS application and are executed one after another in a continuous loop (the Idle Loop). After main returns, a TI-RTOS application calls the startup routine for each TI-RTOS module and then falls into the Idle Loop. Each thread must wait for all others to finish executing before it is called again. The Idle Loop runs continuously except when it is preempted by higher-priority threads. Only functions that do not have hard deadlines should be executed in the Idle Loop.

For CC26x2 devices, the Idle Task allows the Power Policy Manager to enter the lowest allowable power savings.

Kernel Configuration

A TI-RTOS application configures the TI-RTOS kernel using a configuration (.cfg file) that is found within the project. In IAR and CCS projects, this file is found in the application project workspace under the TOOLS folder.

The configuration is accomplished by selectively including or using RTSC modules available to the kernel. To use a module, the .cfg calls xdc.useModule() after which it can set various options as defined in the TI-RTOS Kernel User Guide.

Some of the option that can be configured in the .cfg file include but are not limited to:

• Boot options
• Number of Hwi, Swi, and Task priorities
• Exception and Error handling
• The duration of a System tick (the most fundamental unit of time in the TI-RTOS kernel).
• Defining the application’s entry point and interrupt vector
• TI-RTOS heaps and stacks
• Including pre-compiled kernel and TI-RTOS driver libraries
• System providers (for System_printf())

Whenever a change in the .cfg file is made, you will rerun the XDCTools’ configuro tool. This step is already handled for you as a pre-build step in the provided IAR and CCS examples.

For the CC26x2, a TI-RTOS kernel exists in ROM. Typically for flash footprint savings, the .cfg will include the kernel’s ROM module as shown in Listing 1.

Listing 1. How to include the TI-RTOS kernel in ROM

/* ================ ROM configuration ================ */
/*
 * To use BIOS in flash, comment out the code block below.
 */
var ROM = xdc.useModule('ti.sysbios.rom.ROM');
if (Program.cpu.deviceName.match(/CC26/)) {
    ROM.romName = ROM.CC26X2;
}
else if (Program.cpu.deviceName.match(/CC13/)) {
    ROM.romName = ROM.CC13X2;
}

The TI-RTOS kernel in ROM is optimized for performance. If additional instrumentation is required in your application (typically for debugging), you must include the TI-RTOS kernel in flash which will increase flash memory consumption. Shown below is a short list of requirements to use the TI-RTOS kernel in ROM.

• BIOS.assertsEnabled must be set to false
• BIOS.logsEnabled must be set to false
• BIOS.taskEnabled must be set to true
• BIOS.swiEnabled must be set to true
• BIOS.runtimeCreatesEnabled must be set to true
• BIOS must use the ti.sysbios.gates.GateMutex module
• Clock.tickSource must be set to Clock.TickSource_TIMER
• Semaphore.supportsPriority must be false
• Swi, Task, and Hwi hooks are not permitted
• Swi, Task, and Hwi name instances are not permitted
• Task stack checking is disabled
• Hwi.disablePriority must be set to 0x20
• Hwi.dispatcherAutoNestingSupport must be set to true

For additional documentation in regards to the list described above, see the TI-RTOS Kernel User Guide.

Creating vs. Constructing

Most TI-RTOS modules commonly have _create() and _construct() APIs to initialize primitive instances. The main runtime differences between the two APIs are memory allocation and error handling.

Create APIs perform a memory allocation from the default TI-RTOS heap before initialization. As a result, the application must check the return value for a valid handle before continuing.

Listing 2. Creating a Semaphore

Semaphore_Handle sem;
Semaphore_Params semParams;

Semaphore_Params_init(&semParams);
sem = Semaphore_create(0, &semParams, NULL); /* Memory allocated in here */

if (sem == NULL) /* Check if the handle is valid */
{
    System_abort("Semaphore could not be created");
}

Construct APIs are given a data structure with which to store the instance’s variables. As the memory has been pre-allocated for the instance, error checking may not be required after constructing.

Listing 3. Constructing a Semaphore

Semaphore_Handle sem;
Semaphore_Params semParams;
Semaphore_Struct structSem; /* Memory allocated at build time */

Semaphore_Params_init(&semParams);
Semaphore_construct(&structSem, 0, &semParams);

/* It's optional to store the handle */
sem = Semaphore_handle(&structSem);

Thread Synchronization

The TI-RTOS kernel provides several modules for synchronizing tasks such as Semaphore, Event, and Queue. The following sections discuss these common TI-RTOS primitives.

Semaphores

Semaphores are commonly used for task synchronization and mutual exclusions throughout TI-RTOS applications. Figure 4. shows the semaphore functionality. Semaphores can be counting semaphores or binary semaphores. Counting semaphores keep track of the number of times the semaphore is posted with Semaphore_post(). When a group of resources are shared between tasks, this function is useful. Such tasks might call Semaphore_pend() to see if a resource is available before using one. Binary semaphores can have only two states: available (count = 1) and unavailable (count = 0). Binary semaphores can be used to share a single resource between tasks or for a basic-signaling mechanism where the semaphore can be posted multiple times. Binary semaphores do not keep track of the count; they track only whether the semaphore has been posted.

Figure 4. Semaphore Functionality

Initializing a Semaphore

The following code depicts how a semaphore is initialized in TI-RTOS. Semaphores can be created and constructed as explained in Creating vs. Constructing.

See Listing 2. on how to create a Semaphore.

See Listing 3. on how to construct a Semaphore.

Pending on a Semaphore

Semaphore_pend() is a blocking function call. This call may only be called from within a Task context. A task calling this function will allow lower priority tasks to execute, if they are ready to run. A task calling Semaphore_pend() will block if its counter is 0, otherwise it will decrement the counter by one. The task will remain blocked until another thread calls Semaphore_post() or if the supplied system tick timeout has occurred; whichever comes first. By reading the return value of Semaphore_pend() it is possible to distinguish if a semaphore was posted or if it timed out.

Listing 4. Pending on a Semaphore

bool isSuccessful;
uint32_t timeout = 1000 * (1000/Clock_tickPeriod);

/* Pend (approximately) up to 1 second */
isSuccessful = Semaphore_pend(sem, timeoutInTicks);

if (isSuccessful)
{
    System_printf("Semaphore was posted");
}
else
{
    System_printf("Semaphore timed out");
}

Note

The default TI-RTOS system tick period is 1 millisecond. This default is reconfigured to 10 microseconds for CC26x2 by setting Clock.tickPeriod = 10 in the .cfg file.

Given a system tick of 10 microseconds, timeout in Listing 4. will be approximately 1 second.

Posting a Semaphore

Posting a semaphore is accomplished via a call to Semaphore_post(). A task that is pending on a posted semaphore will transition from a blocked state to a ready state. If no higher priority thread is ready to run, it will allow the previously pending task to execute. If no task is pending on the semaphore, a call to Semaphore_post() will increment its counter. Binary semaphores have a maximum count of 1.

Listing 5. Posting a Semaphore

Semaphore_post(sem);

Event

Semaphores themselves provide rudimentary synchronization between threads. There are cases just the Semaphore itself is enough to understand on what process needs to be triggered. Often however, a specific causes for the synchronization need to be passed across threads as well. To help accomplish this, one can utilize the TI-RTOS Event module.

Events are similar to Semaphores in a sense that each instance of an Event object actually contains a Semaphore. The added advantage of using Events lie in the fact that tasks can be notified of specific events in a thread-safe manner.

Initializing an Event

Creating and constructing Events follow the same guidelines as explained in Creating vs. Constructing. Shown in Listing 6. is an example on how to construct an Event instance.

Listing 6. Constructing an Event

Event_Handle event;
Event_Params eventParams;
Event_Struct structEvent; /* Memory allocated at build time */

Event_Params_init(&eventParams);
Event_construct(&structEvent, 0, &eventParams);

/* It's optional to store the handle */
event = Event_handle(&structEvent);

Pending on an Event

Similar to Semaphore_pend(), a Task thread would typically block on an Event_pend() until an event is posted via an Event_post() or if the specified timeout expired. Shown in Listing 7. is a snippet of a task pending on any of the 3 sample event IDs shown below. BIOS_WAIT_FOREVER is used to prevent a timeout from occurring. As a result, Event_pend() will have one or more events posted in the returned bit-masked value.

Each event returned from Event_pend() has been automatically cleared within the event instance in a thread-safe manner. Therefore, it is only necessary to keep a local copy of posted events. For full details on how to use Event_pend(), see the TI-RTOS Kernel User Guide.

Listing 7. Pending on an Event

#define START_ADVERTISING_EVT         Event_Id_00
#define START_CONN_UPDATE_EVT         Event_Id_01
#define CONN_PARAM_TIMEOUT_EVT        Event_Id_02

void TaskFxn(..)
{
    /* Local copy of events that have been posted */
    uint32_t events;

    while(1)
    {
        /* Wait for an event to be posted */
        events = Event_pend(event,
                            Event_Id_NONE,
                            START_ADVERTISING_EVT |
                            START_CONN_UPDATE_EVT |
                            CONN_PARAM_TIMEOUT_EVT,
                            BIOS_WAIT_FOREVER);

        if (events & START_ADVERTISING_EVT)
        {
            /* Process this event */
        }

        if (events & START_CONN_UPDATE_EVT)
        {
            /* Process this event */
        }

        if (events & CONN_PARAM_TIMEOUT_EVT)
        {
            /* Process this event */
        }
    }
}

Note

The default TI-RTOS system tick period is 1 millisecond. This default is reconfigured to 10 microseconds for CC26xx and CC13xx devices by setting Clock.tickPeriod = 10 in the .cfg file.

Given a system tick of 10 microseconds, timeout in Listing 4. will be approximately 1 second.

Posting an Event

Events may be posted from any TI-RTOS kernel contexts and is simply done by calling Event_post() of the Event instance and the Event ID. Listing 8. shows how a high priority thread such as a Swi could post a specific event.

Listing 8. Posting an Event

#define START_ADVERTISING_EVT         Event_Id_00
#define START_CONN_UPDATE_EVT         Event_Id_01
#define CONN_PARAM_TIMEOUT_EVT        Event_Id_02

void SwiFxn(UArg arg)
{
    Event_post(event, START_ADVERTISING_EVT);
}

Queues

The TI-RTOS Queue module provides a thread-safe unidirectional message passing module operating in a first in, first out (FIFO) basis. Queues are commonly used to allow high priority threads to pass messages to lower priority tasks for deferred processing; therefore allowing low priority tasks to block until necessary to run.

In Figure 5. a queue is configured for unidirectional communication from task A to task B. Task A “puts” messages into the queue and task B “gets” messages from the queue.

Figure 5. Queue Messaging Process

In BLE5-Stack, TI-RTOS Queue functions have been abstracted into functions in util.c See the Queue module documentation in the TI-RTOS Kernel User Guide for the underlying functions. The functions in util.c combine a queue from the Queue module with an event from the Event module to pass messages between threads.

In CC26x2 software, ICall uses queues and events from their respective modules to pass messages between the application and stack tasks. An example of this can be seen in SimpleCentral_enqueueMsg(). A high priority Task, Swi, or Hwi queues a message to the application task. The application task will then process this message in its own context when no other high priority threads are running.

The util module contains a set of abstracted TI-RTOS Queue functions as shown here:

• Util_constructQueue() creates a queue.
• Util_enqueueMsg() puts items into the queue.
• Util_dequeueMsg() gets items from the queue.

Functional Example

Figure 6. and Figure 7. illustrate how a queue is used to enqueue a button press message from a Hwi (to a Swi in the Board Key module) to be post-processed within a task context. This example is taken from the from the simple_central project in BLE5-Stack.

Figure 6. Sequence diagram for enqueuing a message

With interrupts enabled, a pin interrupt can occur asynchronously within a Hwi context. To keep interrupts as short as possible, the work associated to the interrupt is deferred to tasks for processing. In the simple_central example found in BLE5-Stack, pin interrupts are abstracted via the Board Key module. This module notifies registered functions via a Swi callback. In this case, SimpleCentral_keyChangeHandler is the registered callback function.

Step 1 in Figure 6. shows the callback to SimpleCentral_keyChangeHandler when a key is pressed. This event is placed into the application’s queue for processing.

Listing 9. Defining SimpleCentral_keyChangeHandler()

void SimpleCentral_keyChangeHandler(uint8 keys)
{
  SimpleCentral_enqueueMsg(SC_KEY_CHANGE_EVT, keys, NULL);
}

Step 2 in Figure 6. shows how this key press is enqueued for simple_central task. Here, memory is allocated via ICall_malloc() so the message can be added to the queue. Once added, Util_enqueueMsg() will generate a UTIL_QUEUE_EVENT_ID event to signal the application for processing.

Listing 10. Defining SimpleCentral_enqueueMsg()

static uint8_t SimpleCentral_enqueueMsg(uint8_t event, uint8_t state, uint8_t *pData)
{
  scEvt_t *pMsg = ICall_malloc(sizeof(scEvt_t));

  // Create dynamic pointer to message.
  if (pMsg)
  {
    pMsg->hdr.event = event;
    pMsg->hdr.state = state;
    pMsg->pData = pData;

    // Enqueue the message.
    return Util_enqueueMsg(appMsgQueue, syncEvent, (uint8_t *)pMsg);
  }

  return (false);
}

Figure 7. Sequence diagram for dequeuing a message

Step 3 in Figure 7., the simple_central application is unblocked by the posted UTIL_QUEUE_EVENT_ID event where it proceeds to check if messages have been placed in the queue for processing.

Listing 11. Processing application messages

// If RTOS queue is not empty, process app message
if (events & SC_QUEUE_EVT)
{
    scEvt_t *pMsg;
    while (pMsg = (scEvt_t *)Util_dequeueMsg(appMsgQueue))
    {
        // Process message
        SimpleCentral_processAppMsg(pMsg);

        // Free the space from the message
        ICall_free(pMsg);
    }
}

Step 4 in Figure 7., the simple_central application takes the dequeued message and processes it.

Listing 12. Processing key interrupt message

static void SimpleCentral_processAppMsg(sbcEvt_t *pMsg)
{
  switch (pMsg->hdr.event)
  {
    case SC_KEY_CHANGE_EVT:
      SimpleCentral_handleKeys(pMsg->hdr.state);
      break;
    //...
  }
}

Step 5 in Figure 7., the simple_central application can now free the memory allocated in Step 2.

Tasks

TI-RTOS Tasks are equivalent to independent threads that conceptually execute functions in parallel within a single C program. In reality, switching the processor from one task to another helps achieve concurrency. Each Task is always in one of the following modes of execution:

• Running: task is currently running
• Ready: task is scheduled for execution
• Blocked: task is suspended from execution
• Terminated: task is terminated from execution
• Inactive: task is on inactive list

One (and only one) task is always running, even if it is only the Idle Task (see Figure 2.). The current running task can be blocked from execution by calling certain Task module functions, as well as functions provided by other modules like Semaphores. The current task can also terminate itself. In either case, the processor is switched to the highest priority task that is ready to run. See the Task module in the package ti.sysbios.knl section of the TI-RTOS Kernel User Guide for more information on these functions.

Numeric priorities are assigned to tasks, and multiple tasks can have the same priority. Tasks are readied to execute by highest to lowest priority level; tasks of the same priority are scheduled in order of arrival. The priority of the currently running task is never lower than the priority of any ready task. The running task is preempted and rescheduled to execute when there is a ready task of higher priority.

In the simple_peripheral application, the Bluetooth low energy protocol stack task is given the highest priority (5) and the application task is given the lowest priority (1).

Initializing a Task

When a task is initialized, it has its own runtime stack for storing local variables as well as further nesting of function calls. All tasks executing within a single program share a common set of global variables, accessed according to the standard rules of scope for C functions. This set of memory is the context of the task. The following is an example of the application task being constructed.

Listing 13. A TI-RTOS task

#include <xdc/std.h>
#include <ti/sysbios/BIOS.h>
#include <ti/sysbios/knl/Task.h>

/* Task's stack */
uint8_t sbcTaskStack[TASK_STACK_SIZE];

/* Task object (to be constructed) */
Task_Struct task0;

/* Task function */
void taskFunction(UArg arg0, UArg arg1)
{
    /* Local variables. Variables here go onto task stack!! */

    /* Run one-time code when task starts */

    while (1) /* Run loop forever (unless terminated) */
    {
        /*
         * Block on a signal or for a duration. Examples:
         *  ``Sempahore_pend()``
         *  ``Event_pend()``
         *  ``Task_sleep()``
         *
         * "Process data"
         */
    }
}

int main() {

    Task_Params taskParams;

    // Configure task
    Task_Params_init(&taskParams);
    taskParams.stack = sbcTaskStack;
    taskParams.stackSize = TASK_STACK_SIZE;
    taskParams.priority = TASK_PRIORITY;

    Task_construct(&task0, taskFunction, &taskParams, NULL);

    BIOS_start();
}

The task creation is done in the main() function, before the TI-RTOS Kernel’s scheduler is started by BIOS_start(). The task executes at its assigned priority level after the scheduler is started.

TI recommends using an existing application task for application-specific processing. When adding an additional task to the application project, the priority of the task must be assigned a priority within the TI-RTOS priority-level range, defined in the TI-RTOS configuration file (.cfg).

Tip

Reduce the number of Task priority levels to gain additional RAM savings in the TI-RTOS configuration file (.cfg):

Task.numPriorities = 6;

Do not add a task with a priority equal to or higher than the Bluetooth low energy protocol stack task and related supporting tasks. See Standard Project Task Hierarchy for details on the system task hierarchy.

Ensure the task has a minimum task stack size of 512 bytes of predefined memory. At a minimum, each stack must be large enough to handle normal subroutine calls and one task preemption context. A task preemption context is the context that is saved when one task preempts another as a result of an interrupt thread readying a higher priority task. Using the TI-RTOS profiling tools of the IDE, the task can be analyzed to determine the peak task stack usage.

Note

The term created describes the instantiation of a task. The actual TI-RTOS method is to construct the task. See Creating vs. Constructing for details on constructing TI-RTOS objects.

A Task Function

When a task is initialized, a function pointer to a task function is passed to the Task_construct function. When the task first gets a chance to process, this is the function which the TI-RTOS runs. Listing 13. shows the general topology of this Task function.

In typical use cases, the task spends most of its time in the blocked state, where it calls a _pend() API such as Semaphore_pend(). Often, high priority threads such as Hwis or Swis unblock the task with a _post() API such as Semaphore_post().

Clocks

Clock instances are functions that can be scheduled to run after a certain number of system ticks. Clock instances are either one-shot or periodic. These instances start immediately upon creation, are configured to start after a delay, and can be stopped at any time. All clock instances are executed when they expire in the context of a Swi. The following example shows the minimum resolution is the TI-RTOS clock tick period set in the TI-RTOS configuration file (.cfg).

Note

The default TI-RTOS kernel tick period is 1 millisecond. For CC26x2 devices, this is reconfigured in the TI-RTOS configuration file (.cfg):

Clock.tickPeriod = 10;

Each system tick, which is derived from the real-time clock RTC, launches a Clock object that compares the running tick count with the period of each clock to determine if the associated function should run. For higher-resolution timers, TI recommends using a 16-bit hardware timer channel or the sensor controller. See the Clock module in the package ti.sysbios.knl section of the TI-RTOS Kernel User Guide for more information on these functions.

You can use the Kernel’s Clock APIs directly in your application and in addition the Util module also contains a set of abstracted TI-RTOS Clock functions as shown here:

• Util_constructClock() creates a Clock object.
• Util_startClock() starts an existing Clock object.
• Util_restartClock() stops, restarts an existing Clock object.
• Util_isActive() checks if a Clock object is running.
• Util_stopClock() stop an existing Clock object.
• Util_rescheduleClock() reconfigure an existing Clock object.

Functional Example

The following example was taken from the simple_peripheral project in BLE5-Stack.

Figure 8. Triggering Clock objects

Step 1 in Triggering Clock objects constructs the Clock object via Util_constructClock(). After the example entered a connected state, it will then start the Clock object via a Util_startClock().

Listing 14. Constructing periodicClock Clock object in simple_peripheral

// Clock instances for internal periodic events.
static Clock_Struct periodicClock;

// Create one-shot clocks for internal periodic events.
Util_constructClock(&periodicClock, SimplePeripheral_clockHandler,
    SP_PERIODIC_EVT_PERIOD, 0, false, SP_PERIODIC_EVT);

Step 2 in Triggering Clock objects, after the Clock object’s timer expired, it will execute SimplePeripheral_clockHandler() within a Swi context. As this call cannot be blocked and blocks all Tasks, it is kept short by invoking an Event_post(SP_PERIODIC_EVT) for post processing in simple_peripheral.

Listing 15. Defining SimplePeripheral_clockHandler()

static void SimplePeripheral_clockHandler(UArg arg)
{
    /* arg is passed in from Clock_construct() */
    Event_post(events, arg);
}

Attention

Clock functions must not call blocking kernel APIs or TI-RTOS driver APIs! Executing long routines will impact real-time constraints placed in high priority tasks allocated for wireless protocol stacks!

Step 3 in Triggering Clock objects, the simple_peripheral task is unblocked due the Event_post(SP_PERIODIC_EVT), where it proceeds to invoke the SimplePeripheral_performPeriodicTask() function. Afterwards, to restart the periodic execution of this function, it will restart the periodicClock Clock object.

Listing 16. Servicing the SP_PERIODIC_EVT event

if (events & SP_PERIODIC_EVT)
{
  // Perform periodic application task
  SimplePeripheral_performPeriodicTask();

  Util_startClock(&periodicClock);
}

Power Management

All power-managment functionality is handled by the TI-RTOS power driver and are used by the peripheral drivers (e.g. UART, SPI, I2C, etc..). Applications can prevent, if they choose, the CC26x2 from entering low power modes by setting a power constraint.

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 awake.

More information on power-management functionality, including the API and a sample use case for a custom UART driver, can be found in the TI-RTOS Power Management for CC26x2 included in the TI-RTOS install. These APIs are required only when using a custom driver.

Also see Measuring Bluetooth Smart Power Consumption (SWRA478) for steps to analyze the system power consumption and battery life.