MSG_DEFAULT_SIZE
err = send_msg(mgr, request, MSG_DEFAULT_SIZE, 1, ¬if_event); /* send and mark the notification event pending */
err = send_msg(mgr, request, MSG_DEFAULT_SIZE, 0, &message_frame);
static u32 mixart_msg_data[MSG_DEFAULT_SIZE / 4];
((MSG_DEFAULT_SIZE - sizeof(u32)) / sizeof(struct mixart_sample_pos))