Boost Embedded Performance with the Lightweight C Event Library lwevt

Overview

lwevt is a lightweight event‑management library written in C for embedded systems. It provides a platform‑independent mechanism for defining custom event types and associated data, with a simple API for registration and dispatch.

Key Features

Platform‑independent, no architecture‑specific code.

Customizable event types and associated data defined by the application.

Easy to use and maintain.

MIT license.

Getting Started

Clone the repository:

git clone --recurse-submodules https://github.com/MaJerle/lwevt

Basic Usage

#include <stdio.h>
#include <string.h>
#include "lwevt/lwevt.h"

static void prv_evt_fn_1(lwevt_t *e) {
    switch ((unsigned)e->type) {
        case LWEVT_TYPE_MY_EXT_1:
            printf("Event fn 1, LWEVT_TYPE_MY_EXT_1 - with data: a: %d, b: %d
",
                   (int)e->msg.a.a, (int)e->msg.a.b);
            break;
        default:
            break;
    }
}

static void prv_evt_fn_2(lwevt_t *e) {
    switch ((unsigned)e->type) {
        case LWEVT_TYPE_MY_EXT_2:
            printf("Event fn 2, LWEVT_TYPE_MY_EXT_2 - with data: a: %d, b: %d
",
                   (int)e->msg.b.a, (int)e->msg.b.b);
            break;
        default:
            break;
    }
}

int main(void) {
    lwevt_t *evt;
    lwevt_t evt_local;

    lwevt_init();
    lwevt_register(prv_evt_fn_1);
    lwevt_register(prv_evt_fn_2);

    evt = lwevt_get_handle();
    evt->msg.a.a = 1;
    evt->msg.a.b = 2;
    lwevt_dispatch(LWEVT_TYPE_MY_EXT_1);

    evt_local.msg.b.a = 3;
    evt_local.msg.b.b = 4;
    lwevt_dispatch_ex(&evt_local, LWEVT_TYPE_MY_EXT_2);
    return 0;
}

The library provides a global static event handle accessed via lwevt_get_handle(). Functions lwevt_dispatch() and lwevt_dispatch_ex() are available when LWEVT_CFG_ENABLE_DEFAULT_HANDLE is enabled.

Thread‑Safety

In multithreaded environments the caller must ensure that accesses to the default handle and dispatch functions are protected. Using local lwevt_t variables with lwevt_dispatch_ex() avoids global synchronization.

Event Type Definition (X‑Macro)

Event types and payload structures are defined in a user‑maintained lwevt_types.h using the X‑Macro technique, for example:

LWEVT_TYPE_BASIC(LWEVT_TYPE_MY_BASIC_1)
LWEVT_TYPE_BASIC(LWEVT_TYPE_MY_BASIC_2)

LWEVT_TYPE_EXT(LWEVT_TYPE_MY_EXT_1, struct { int a; int b; } a)
LWEVT_TYPE_EXT(LWEVT_TYPE_MY_EXT_2, struct { int a; int b; } b)

The main header lwevt.h expands these macros to generate the lwevt_type_t enum and the lwevt_t structure, which contains a type field and a union msg that holds the event data.

Generated Event Type Enum

typedef enum {
    #define LWEVT_TYPE_BASIC(name)     name,
    #define LWEVT_TYPE_EXT(name, data) name,
    #include "lwevt/lwevt_type.h"
    LWEVT_TYPE_LAST
} lwevt_type_t;

Event Structure

typedef struct {
    lwevt_type_t type;   /* Event type */
    union {
        #define LWEVT_TYPE_EXT(name, data) data;
        #include "lwevt/lwevt_type.h"
        const unsigned int dummy; /* Fallback */
    } msg;               /* Payload */
} lwevt_t;

Repository: https://github.com/MaJerle/lwevt