Data Queue Vs MailBox: Refer status

① Difference between referring Data Queue and Mailbox

ref_dtq() returns the task id for waiting receive and send tasks and number of data elements in the data queue.

ref_mbx() has to return either the pointer to the message at the top of the message queue or the task ID which is waiting at the receive waiting queue.

② ITRON implementation of referring data queue

ER ref_dtq(ID dtqid, T_RDTQ *pk_rdtq)
{
        Sanity check on arguments;
        enter critical section;
        store the number of data elements in the data queue into the pk_rdtq->sdtqcnt;
        check the receive waiting task queue;
        if (any task exists) {
                store the task id into the pk_rdtq->stsk_id;
        }
        else {
                pk_rdtq->stsk_id = TSK_NONE;
        }
        check the send waiting task queue;
        if (any task exists) {
                store the task id into the pk_rdtq->rtsk_id;
        }
        else {
                pk_rdtq->rtsk_id = TSK_NONE;
        }
        exit critical section;
        return E_OK;
}

③ ITRON implementation of referring Mailbox

ER ref_mbx(ID mbxid, T_RMBX *pk_rmbx)
{
        Sanity check on arguments;
        enter critical section;
        /* Check for the pending message first */
        get the head of message queue;
        for (each priority level of the messages) {
                get the head pointer to the message queue for the particular level;
                if (there is message) {
                        store the pointer to the message into the pk_rmbx->pk_msg;
                        make pk_rmbx->wtskid = TSK_NONE;
                        return E_OK;
                }
        }
        /* No message; So, check for any waiting task */
        make the pk_rmbx->pk_msg =NULL;
        check for any waiting receive task over the queue;
        if (there is any task) {
                store the task id into the pk_rmbx->wtskid;
                return E_OK;
        }
        /* No task either */
        pk_rmbx->wtskid = TSK_NONE;
        return E_OK;
}
Enjoy embedded RTOS...