Multiple Advertisements Using the Timeslot API

[Cory Mast]

Hello,

I am currently designing a project that will advertise as two different beacons simultaneously using the Timeslot API. I have successfully implemented the nRF51-multi-role-conn-observer-advertiser example on GitHub and by using the nRF Master Control Panel application on android I can successfully see both advertisements. The problem is that I am noticing some irregularities in the waveform when I run the Timeslot advertisement alongside the SoftDevice advertisement. If i make the call to sd_ble_gap_adv_start() by itself I get an ideal waveform and if I make the call to btle_hci_adv_enable(BTLE_ADV_ENABLE) by itself I again get the ideal waveform. If I make both calls together, I get the irregularity. I have attached a screen capture from my oscilloscope to show the irregularity.

I have set up my Timeslot advertisement to advertise at a rate of 100ms and my SoftDevice to advertise at a rate of 1285ms

static void timeslot_advertiser_init(void)
{
btle_cmd_param_le_write_advertising_parameters_t adv_params;

/* we use software interrupt 1 */
btle_hci_adv_init(SWI1_IRQn);

/* BLE on-air address */
static ble_gap_addr_t ble_addr;

uint32_t err_code = sd_ble_gap_address_get(&ble_addr);
   APP_ERROR_CHECK(err_code);


memcpy((void*) &adv_params.direct_address[0], (void*) &ble_addr.addr[0], BTLE_DEVICE_ADDRESS__SIZE);

/* want to maximize potential scan requests */
adv_params.channel_map = BTLE_CHANNEL_MAP_ALL;
adv_params.direct_address_type = BTLE_ADDR_TYPE_RANDOM;
adv_params.filter_policy = BTLE_ADV_FILTER_ALLOW_ANY;
adv_params.interval_min = BLE_ADV_INTERVAL_100MS;
adv_params.interval_max = BLE_ADV_INTERVAL_105MS;

adv_params.own_address_type = BTLE_ADDR_TYPE_RANDOM;

/* Only want non-connectable requests */
adv_params.type = BTLE_ADV_TYPE_NONCONN_IND;

btle_hci_adv_params_set(&adv_params);
}

The waveform irregularity appears to occur about once every second.I am having difficulty understanding where this irregularity comes from and how to remove it. Any help you could provide would be greatly appreciated.

I am using the S110 SoftDevice version 7.1.0 and SDK 7.2.0

Thank You,

Cory

[Cory Mast]

After much investigating I believe I finally understand the timeslot well enough to update with a response.

It appears that if the advertisement interval of the soft device and the timeslot interval are too close together, and even if they are spaced far apart, there is the chance that the soft device and the timeslot advertisement can collide. When this was happening, my event handler was aborting the timeslot and then ordering another timeslot advertisement. I believe the multiple advertisement burst was occurring when my code would order another timeslot advertisement while still being blocked by the soft device and attempt to abort and order and then abort and order until it finally wasn't being blocked any more. By using the extend functionality of the timeslot api i was able to overcome this problem.

Thank you for your help and great support!

[Ulrich Myhre]

Great that you found a solution! I wonder though, why isn't just changing the advertising data regularly enough for your implementation? Do you require very different advertising parameters for the two beacons?