Event Manager

Events
Modules
Configuration
Implementing events and modules
Event Manager extensions
- Tracing hooks
- Shell integration
API documentation

The Event Manager is a piece of software that supports development of consistent, modular, event-based applications. In an event-based application, parts of the application functionality are separated into isolated modules that communicate with each other using events. Events are submitted by modules and other modules can subscribe and react to them. The Event Manager acts as coordinator of the event-based communication.

For a usage example of the Event Manger module and event structure in the nRF Connect SDK, see the Common Application Framework (CAF).

See the Event Manager sample for a simple example of how to use the Event Manager.

Events 

Events are structured data types that are defined by the application and can contain additional data.

The Event Manager handles the events by processing and propagating all of them to the modules (listeners) that subscribe to a specific event. Multiple modules can subscribe to the same event. As part of this communication, listeners can process events differently based on their type.

The Event Manager provides API for defining, creating, and subscribing events. See Implementing an event type for details about how to create custom event types.

Modules 

Modules are separate source files that can subscribe to every defined event. You can use events for communication between modules.

There is no limitation as to how many events each module can subscribe to. An application can have as many modules as required.

The Event Manager provides an API for subscribing modules to specific events defined in the application. When a module subscribes to a specific event, it is called a listener module. Every listener is identified by a unique name.

Configuration 

To use Event Manager, enable it using the CONFIG_EVENT_MANAGER Kconfig option and initialize it in your main.c file. Initializing the Event Manager allows it to handle submitted events and deliver them to modules that subscribe to the specified event type.

Complete the following steps:

Enable the CONFIG_EVENT_MANAGER Kconfig option.
Include event_manager.h in your main.c file.
Call event_manager_init().

Implementing events and modules 

If an application module is supposed to react to an event, your application must implement an event type, submit the event, and register the module as listener. Read the following sections for details.

Implementing an event type 

If you want to easily create and implement custom event types, the Event Manager provides macros to add a new event type in your application. Complete the following steps:

Create a header file for the event type you want to define
Create a source file for the event type

Create a header file

To create a header file for the event type you want to define:

Make sure the header file includes the Event Manager header file:
```
#include <event_manager.h>
```
Define the new event type by creating a structure that contains an event_header named header as the first field.
Optionally, add additional custom data fields to the structure.
Declare the event type with the EVENT_TYPE_DECLARE macro, passing the name of the created structure as an argument.

The following code example shows a header file for the event type sample_event:

#include <event_manager.h>

struct sample_event {
        struct event_header header;

        /* Custom data fields. */
        int8_t value1;
        int16_t value2;
        int32_t value3;
};

EVENT_TYPE_DECLARE(sample_event);

In some use cases, the length of the data associated with an event may vary. You can use the EVENT_TYPE_DYNDATA_DECLARE macro instead of EVENT_TYPE_DECLARE to declare an event type with variable data size. In such case, add the data with the variable size as the last member of the event structure. For example, you can add variable sized data to the previously defined event by applying the following change to the code:

#include <event_manager.h>

struct sample_event {
        struct event_header header;

        /* Custom data fields. */
        int8_t value1;
        int16_t value2;
        int32_t value3;
        struct event_dyndata dyndata;
};

EVENT_TYPE_DYNDATA_DECLARE(sample_event);

In this example, the event_dyndata structure contains the following information:

A zero-length array that is used as a buffer with variable size (event_dyndata.data).
A number representing the size of the buffer (event_dyndata.size).

Create a source file

To create a source file for the event type you defined in the header file:

Include the header file for the new event type in your source file.
Define the event type with the EVENT_TYPE_DEFINE macro. Pass the name of the event type as declared in the header along with additional parameters. For example, you can provide a function that fills a buffer with a string version of the event data (used for logging).

The following code example shows a source file for the event type sample_event:

#include "sample_event.h"

static int log_sample_event(const struct event_header *eh, char *buf,
                            size_t buf_len)
{
        struct sample_event *event = cast_sample_event(eh);

        EVENT_MANAGER_LOG(eh, "val1=%d val2=%d val3=%d", event->value1,
                        event->value2, event->value3);
        return 0;
}

EVENT_TYPE_DEFINE(sample_event,      /* Unique event name. */
                  true,              /* Event logged by default. */
                  log_sample_event,  /* Function logging event data. */
                  NULL);             /* No event info provided. */

Note

There is a deprecated way of logging Event Manager events by writing a string to the provided buffer that will be supported until a future release of nRF Connect SDK.

Submitting an event 

To submit an event of a given type, for example sample_event:

Allocate the event by calling the function with the name new_event_type_name. For example, new_sample_event().
Write values to the data fields.
Use EVENT_SUBMIT to submit the event.

The following code example shows how to create and submit an event of type sample_event that has three data fields:

/* Allocate event. */
struct sample_event *event = new_sample_event();

/* Write data to datafields. */
event->value1 = value1;
event->value2 = value2;
event->value3 = value3;

/* Submit event. */
EVENT_SUBMIT(event);

If an event type also defines data with variable size, you must pass also the size of the data as an argument to the function that allocates the event. For example, if the sample_event also contains data with variable size, you must apply the following changes to the code:

/* Allocate event. */
struct sample_event *event = new_sample_event(my_data_size);

/* Write data to datafields. */
event->value1 = value1;
event->value2 = value2;
event->value3 = value3;

/* Write data with variable size. */
memcpy(event->dyndata.data, my_buf, my_data_size);

/* Submit event. */
EVENT_SUBMIT(event);

After the event is submitted, the Event Manager adds it to the processing queue. When the event is processed, the Event Manager notifies all modules that subscribe to this event type.

Note

Events are dynamically allocated and must be submitted. If an event is not submitted, it will not be handled and the memory will not be freed.

Registering a module as listener 

If you want a module to receive events managed by the Event Manager, you must register it as a listener and you must subscribe it to a given event type.

To turn a module into a listener for specific event types, complete the following steps:

Include the header files for the respective event types, for example, #include "sample_event.h".
Implement an Event handler function and define the module as a listener with the EVENT_LISTENER macro, passing both the name of the module and the event handler function as arguments.
Subscribe the listener to specific event types.

For subscribing to an event type, the Event Manager provides three types of subscriptions, differing in priority. They can be registered with the following macros:

EVENT_SUBSCRIBE_FIRST - notification as the first subscriber
EVENT_SUBSCRIBE_EARLY - notification before other listeners
EVENT_SUBSCRIBE - standard notification
EVENT_SUBSCRIBE_FINAL - notification as the last, final subscriber

There is no defined order in which subscribers of the same priority are notified.

The module will receive events for the subscribed event types only. The listener name passed to the subscribe macro must be the same one used in the macro EVENT_LISTENER.

Implementing an event handler function

The event handler function is called when any of the subscribed event types are being processed. Only one event handler function can be registered per listener. Therefore, if a listener subscribes to multiple event types, the function must handle all of them.

The event handler gets a pointer to the event_header structure as the function argument. The function should return true to consume the event, which means that the event is not propagated to further listeners, or false, otherwise.

To check if an event has a given type, call the function with the name is_event_type_name (for example, is_sample_event()), passing the pointer to the event header as the argument. This function returns true if the event matches the given type, or false otherwise.

To access the event data, cast the event_header structure to a proper event type, using the function with the name cast_event_type_name (for example, cast_sample_event()), passing the pointer to the event header as the argument.

Code example

The following code example shows how to register an event listener with an event handler function and subscribe to the event type sample_event:

#include "sample_event.h"

static bool event_handler(const struct event_header *eh)
{
        if (is_sample_event(eh)) {

                /* Accessing event data. */
                struct sample_event *event = cast_sample_event(eh);

                int8_t v1 = event->value1;
                int16_t v2 = event->value2;
                int32_t v3 = event->value3;

                /* Actions when received given event type. */
                foo(v1, v2, v3);

                return false;
        }

        return false;
}

EVENT_LISTENER(sample_module, event_handler);
EVENT_SUBSCRIBE(sample_module, sample_event);

The variable size data is accessed in the same way as the other members of the structure defining an event.

Event Manager extensions 

The Event Manager provides additional features that could be helpful when debugging event-based applications.

Tracing hooks 

Event Manager provides tracing hooks that you can use at run time to get information about Event Manager initialization, event submission, and event execution. The hooks are provided as weak functions. You can override them for interacting with a custom profiler or for other purposes.

The following weak functions are provided by Event Manager as hooks:

event_manager_trace_event_execution()
event_manager_trace_event_submission()
event_manager_trace_event_init()
event_manager_alloc()
event_manager_free()

For details, refer to API documentation.

Shell integration 

Shell integration is available to display additional information and to dynamically enable or disable logging for given event types.

The Event Manager is integrated with Zephyr’s Shell module. When the shell is turned on, an additional subcommand set (event_manager) is added.

This subcommand set contains the following commands:

show_listeners: Show all registered listeners.
show_subscribers: Show all registered subscribers.
show_events: Show all registered event types. The letters “E” or “D” indicate if logging is currently enabled or disabled for a given event type.
enable or disable: Enable or disable logging. If called without additional arguments, the command applies to all event types. To enable or disable logging for specific event types, pass the event type indexes, as displayed by show_events, as arguments.

API documentation 

Header file: include/event_manager.h

Source files: subsys/event_manager/

group event_manager

Event Manager.

Defines

EVENT_LISTENER(lname, cb_fn)

Create an event listener object.

Parameters

lname – Module name.
cb_fn – Pointer to the event handler function.

EVENT_SUBSCRIBE_FIRST(lname, ename)

Subscribe a listener to an event type as first module that is being notified.

Parameters

lname – Name of the listener.
ename – Name of the event.

EVENT_SUBSCRIBE_EARLY(lname, ename)

Subscribe a listener to the early notification list for an event type.

Parameters

lname – Name of the listener.
ename – Name of the event.

EVENT_SUBSCRIBE(lname, ename)

Subscribe a listener to the normal notification list for an event type.

Parameters

lname – Name of the listener.
ename – Name of the event.

EVENT_SUBSCRIBE_FINAL(lname, ename)

Subscribe a listener to an event type as final module that is being notified.

Parameters

lname – Name of the listener.
ename – Name of the event.

EVENT_TYPE_DECLARE(ename)

Declare an event type.

This macro provides declarations required for an event to be used by other modules.

Parameters

ename – Name of the event.

EVENT_TYPE_DYNDATA_DECLARE(ename)

Declare an event type with dynamic data size.

This macro provides declarations required for an event to be used by other modules. Declared event will use dynamic data.

Parameters

ename – Name of the event.

EVENT_TYPE_DEFINE(ename, init_log_en, log_fn, ev_info_struct)

Define an event type.

This macro defines an event type. In addition, it defines functions specific to the event type and the event type structure.

For every defined event, the following functions are created, where event_type is replaced with the given event type name ename (for example, button_event):

new_event_type - Allocates an event of a given type.
is_event_type - Checks if the event header that is provided as argument represents the given event type.
cast_event_type - Casts the event header that is provided as argument to an event of the given type.

Parameters

ename – Name of the event.
init_log_en – Bool indicating if the event is logged by default.
log_fn – Function to stringify an event of this type.
ev_info_struct – Data structure describing the event type.

ASSERT_EVENT_ID(id)

Verify if an event ID is valid.

The pointer to an event type structure is used as its ID. This macro validates that the provided pointer is within the range where event type structures are defined.

Parameters

id – ID.

EVENT_SUBMIT(event)

Submit an event.

This helper macro simplifies the event submission.

Parameters

event – Pointer to the event object.

EVENT_MANAGER_LOG(eh, ...)

Log event.

This helper macro simplifies event logging.

Parameters

eh – Pointer to the event header of the event that is processed by Event Manager.
... – printf- like format string and variadic list of arguments corresponding to the format string.

Functions

int event_manager_init(void)

Initialize the Event Manager.

Return values: 0 – If the operation was successful. Error values can be added by overwriting event_manager_trace_event_init function.

void event_manager_trace_event_execution(const struct event_header *eh, bool is_start)

Trace event execution. The behavior of this function depends on the actual implementation. The default implementation of this function is no-operation. It is annotated as weak and is meant to be overridden by layer adding support for profiling mechanism.

Parameters

eh – Pointer to the event header of the event that is processed by Event Manager.
is_start – Bool value indicating if this occurrence is related to start or end of the event processing.

void event_manager_trace_event_submission(const struct event_header *eh, const void *trace_info)

Trace event submission. The behavior of this function depends on the actual implementation. The default implementation of this function is no-operation. It is annotated as weak and is meant to be overridden by layer adding support for profiling mechanism.

Parameters

eh – Pointer to the event header of the event that is processed by Event Manager.
trace_info – Custom event description for profiling.

int event_manager_trace_event_init(void)

Initialize tracing in the Event Manager. The behavior of this function depends on the actual implementation. The default implementation of this function is no-operation. It is annotated as weak and is meant to be overridden by layer adding support for profiling mechanism.

Return values: 0 – If the operation was successful. Error values can be added by overwriting this function.

void *event_manager_alloc(size_t size)

Allocate event. The behavior of this function depends on the actual implementation. The default implementation of this function is same as k_malloc. It is annotated as weak and can be overridden by user.

Parameters

size – Amount of memory requested (in bytes).

Return values

Address – of the allocated memory if successful, otherwise NULL.

void event_manager_free(void *addr)

Free memory occupied by the event. The behavior of this function depends on the actual implementation. The default implementation of this function is same as k_free. It is annotated as weak and can be overridden by user.

Parameters

addr – Pointer to previously allocated memory.