Sensor status message. Property length (NCS 1.6)

[ipshiv]

Good day!

I have a question about length in MPID. In current implementation size measures in uint16 size and this brings lot's of troubles when you try to decode values: 8 bit and 16 bit have same size, 24 bit and 32 bit does also.

Is it a bug and size should be calculated in bytes or I missed something in Mesh model specification?

[Elfving]

Hey Ivan!

Just letting you know that I am looking into it, but I will have to get back to you.

Best regards,

Elfving

[ipshiv]

Sorry for late response.

We had a sensor server \ client, more than a year ago, written for MESH SDK and it still working on legacy devices (new one use NCS).

We used next function to parse incoming data

typedef struct __attribute((packed))
{
	uint8_t a_b_format : 1;					/**< Format A tag, 0b0. The Format field is a 1-bit bit field that identifies the format of the Length and Property ID fields, as decribed 4.2.14 Sensor Status */
	uint8_t length : 4;					/**< Length of the Property Value */
	uint16_t prop_id : 11;					/**< Property identifying a sensor */
} generic_sensor_format_a_header_t;


static void parse_status_data(uint16_t src, uint16_t dst,
				const uint8_t *p_buff, uint16_t length)
{
	uint16_t shift = 0;
	generic_sensor_format_a_header_t *header;
	uint8_t i = 0;
	while (shift < length) {
		header = (generic_sensor_format_a_header_t *)(p_buff + shift);

		shift += (sizeof(generic_sensor_format_a_header_t));
		i++;
		__LOG(LOG_SRC_APP,
		      LOG_LEVEL_DBG3,
		      "%d >> ID:%d Length:%d, left %d\n",
		      i,
		      header->prop_id,
		      header->length,
		      length - header->length);
 		size_t data_size = header->length * sizeof(uint16_t);
		shift += data_size;
	}
}

And, for example, I receive data from NCS's sensor server with data

1 >> ID:82 Length:2, left 23

82 in decimal equals 0x0052

#define BT_MESH_PROP_ID_PRESENT_DEV_INPUT_POWER 0x0052
/** Present device input power
 *
 *  Channels:
 *  - Present Device Input Power
 *    - Unit: Watt
 *    - Encoding: 24 bit unsigned scalar (Resolution: 0.1 W)
 *    - Range: 0 to 1677721.4
 */
extern const struct bt_mesh_sensor_type bt_mesh_sensor_present_dev_input_power;

Of course it ruins all marshalled data