How to handle and receive messages

Message callbacks of services can be difficult to use when a project has high real-time constraints.

Luos engine provides two different configurations allowing you to choose the best way for you to deal with messages. The message handling configuration is set during the initialization of a service.

Configuration	execution type
Callback (default)	runtime callback
Polling	no callback

The following sections detail how the different configurations work.

Callback configuration

This configuration is the default and most common setup. In this configuration, Luos engine directly calls the service callback during runtime. The time between the physical reception of a message and the callback may vary depending on the Luos_loop() function execution frequency.

With this configuration you have no real constraints on the callback's time of execution, you can then reply to a message directly on the callback.

To setup this configuration, you have to simply setup the callback at service creation.

Here is a code example with a button:

void Button_MsgHandler(service_t *service, const msg_t *msg)
{
    if (msg->header.cmd == ASK_PUB_CMD)
    {
        // The message is filled with global variables with proper data
        msg_t pub_msg;
        pub_msg.header.cmd         = IO_STATE;
        pub_msg.header.target_mode = SERVICEID;
        pub_msg.header.target      = msg->header.source;
        pub_msg.header.size        = sizeof(char);
        pub_msg.data[0]            = HAL_GPIO_ReadPin(BTN_GPIO_Port, BTN_Pin);
        // Sending the message
        Luos_SendMsg(service, &pub_msg);
        return;
    }
}

void Button_Init(void)
{
    // service creation: (callback, service type, Default alias)
    service_t* service = Luos_CreateService(Button_MsgHandler, STATE_TYPE, "button");
}

void Button_Loop(void)
{
}

Polling configuration

This configuration is often used in Arduino libraries to receive information in a basic way. This method allows you to handle messages only when the user wants to do it in the loop of the service.

To set up this configuration, you have to create your service without any callbacks.

See the following code as an example, with a button:

service_t* service;
void Button_Init(void)
{
    service = Luos_CreateService(0, STATE_TYPE, "button");
}

void Button_Loop(void)
{
    if (Luos_NbrAvailableMsg())
    {
        msg_t *msg = Luos_ReadMsg(service);
        if (msg->header.cmd == ASK_PUB_CMD)
        {
            // The message is filled with global variables with proper data
            msg_t pub_msg;
            pub_msg.header.cmd         = IO_STATE;
            pub_msg.header.target_mode = SERVICEID;
            pub_msg.header.target      = msg->header.source;
            pub_msg.header.size        = sizeof(char);
            pub_msg.data[0]            = HAL_GPIO_ReadPin(BTN_GPIO_Port, BTN_Pin);
            // Sending the message
            Luos_SendMsg(service, &pub_msg);
        }
    }
}