+void create_send(send_t *sleeping_sends, pheap_t *sleeps_heap,
+ uint32_t timestamp, u16_t seq);
+
+/* When do we next need to send something (in seconds since boot)?
+ * Returns -1 if there's nothing pending. */
+int32_t next_scheduled_send(send_t *sleeping_sends, pheap_t *sleeps_heap);
+