+/* usage:
+ * rpi_prop(RPI_TAG_WHATEVER, foo, bar);
+ * rpi_prop(RPI_TAG_XYZZY, 42);
+ * if(rpi_prop_send() != -1) {
+ * struct rpi_prop *prop;
+ * while((prop = rpi_prop_next())) {
+ * ... process response tags ...
+ * }
+ * }
+ */
+void rpi_prop(int id, ...);
+int rpi_prop_send(void);
+struct rpi_prop *rpi_prop_next(void);
+/* find specific tag in response */
+struct rpi_prop *rpi_prop_find(int id);
+