Synchronisation errors with Distance Measurement (DM)

RE: Synchronisation errors with Distance Measurement (DM)

ptejasv — Tue, 26 Sep 2023 13:57:25 GMT

I used the same method as the DM sample, connection oriented BLE with dm_request_add() triggered as part of the advertising callbacks.

On the initiator side, I called dm_request_add() in the callback for matching scan filters:

bool handle_adv(struct bt_data *data, void *user_data) {
	struct dm_request req;

    switch(data->type) {
		case BT_DATA_UUID128_ALL:
			bt_addr_le_copy(&req.bt_addr, user_data);
			req.role = DM_ROLE_INITIATOR;
			req.ranging_mode = DM_RANGING_MODE_MCPD;
			req.rng_seed = sys_cpu_to_le32(RNG_SEED);
			req.start_delay_us = 0;
			req.extra_window_time_us = 0;

			dm_request_add(&req); // this is where dm is triggered
			break;
	}

	return true;
}

static void scan_filter_match(struct bt_scan_device_info *device_info,
					struct bt_scan_filter_match *filter_match,
					bool connectable)
{
	bt_addr_le_t addr;

	bt_addr_le_copy(&addr, device_info->recv_info->addr);
	bt_data_parse(device_info->adv_data, handle_adv, &addr);
}

BT_SCAN_CB_INIT(scan_cb, scan_filter_match, NULL, NULL, NULL);

On the reflector side, it's called during the extended advertising callback for when the reflector's BLE advertisement is scanned:

static void adv_scanned_cb(struct bt_le_ext_adv *adv,
			struct bt_le_ext_adv_scanned_info *info) {
	struct dm_request req;

	bt_addr_le_copy(&req.bt_addr, info->addr);
	req.role = DM_ROLE_REFLECTOR;
	req.ranging_mode = DM_RANGING_MODE_MCPD;
	req.rng_seed = sys_cpu_to_le32(RNG_SEED);
	req.start_delay_us = 0;
	req.extra_window_time_us = 0;

	dm_request_add(&req);
}

const static struct bt_le_ext_adv_cb adv_cb = {
	.scanned = adv_scanned_cb,
};

adv_cb is just from the external advertisement creation in start_adv().

err = bt_le_ext_adv_create(adv_param, &adv_cb, &adv);

I stuck to what the sample used, but there might be other ways to do it.

RE: Synchronisation errors with Distance Measurement (DM)

syed_ — Tue, 26 Sep 2023 05:04:50 GMT

Hi,

ptejasv have you used connection oriented or connection less ble communication?

If Connection oriented, then can you please suggest when to trigger dm_add_request() on both sides.

Best regards,

syed

RE: Synchronisation errors with Distance Measurement (DM)

ptejasv — Thu, 01 Jun 2023 03:54:36 GMT

I tried that and everything seems to work fine now. I didn't realise it was that trivial of an error. Thanks for your help anyway!

RE: Synchronisation errors with Distance Measurement (DM)

Simonr — Wed, 31 May 2023 10:48:30 GMT

Let me know if you're still having trouble after setting the rng_seed values identical on initiator and reflector!

Best regards,

Simon

RE: Synchronisation errors with Distance Measurement (DM)

ptejasv — Wed, 31 May 2023 08:55:22 GMT

I just re-read the documentation and realised the rng seed should be the same on both initiator and reflector. Will update once I fix that issue.