samples: mesh_badge: fix unknown sensor status message

When the value of an unknown sensor property ID is requested, the length
field should represent the value of zero, as explain in the comment in
sens_unknown_fill. However the marshalled representation of a zero
length is wrong in the code. The format A uses a 1-based uint4 length
value, so the range 0x0–0xF represents the range 1-16. The zero length
is represented by format B using the 0x7F value.

Signed-off-by: Aurelien Jarno <[email protected]>

Author: aurel32

samples/boards/reel_board/mesh_badge/src/mesh.c

@@ -223,16 +223,19 @@ static void sens_temperature_celsius_fill(struct net_buf_simple *msg)
 
 static void sens_unknown_fill(u16_t id, struct net_buf_simple *msg)
 {
-	struct sensor_hdr_a hdr;
+	struct sensor_hdr_b hdr;
 
 	/*
 	 * When the message is a response to a Sensor Get message that
 	 * identifies a sensor property that does not exist on the element, the
 	 * Length field shall represent the value of zero and the Raw Value for
-	 * that property shall be omitted. (Mesh model spec 1.0, 4.2.14)
+	 * that property shall be omitted. (Mesh model spec 1.0, 4.2.14).
+	 *
+	 * The length zero is represented using the format B and the special
+	 * value 0x7F.
 	 */
-	hdr.format = SENSOR_HDR_A;
-	hdr.length = 0U;
+	hdr.format = SENSOR_HDR_B;
+	hdr.length = 0x7FU;
 	hdr.prop_id = id;
 
 	net_buf_simple_add_mem(msg, &hdr, sizeof(hdr));