BLE scan raw data (p_data) gives incomplete data.

[Neeraj Dhekale]

I am trying to display the p_data received data using below inside NRF_BLE_SCAN_EVT_NOT_FOUND case but I am receiving the below data.

2|1|6|1a|ff|4c|0|2|15|ff|ff|0|0|ff|ff|0|0|ff|ff|0|0|ff|ff|0|0|ff|11|2|a5|bf|6a|0|2c|39|0|20|1f|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|

instead of receiving

2|1|6|1a|ff|4c|0|2|15|ff|ff|0|0|ff|ff|0|0|ff|ff|0|0|ff|ff|0|0|ff|11|2|a5|bf|2|a|4|a|16|0|ff|55|ff|11|2|a5|41|88|9|9|54|43|5a|30|30|31|37|36

Note: above payload, HEX data is separated by '|' symbol.

In the above payload data type Type: a and Type: 16 is not getting displayed on the received data. But on the contrary, note even though we can't see it on raw data but we can fetch the data by using ble_advdata_parse() function. why this is happening ? why so?

I have even tried to increase NRF_BLE_SCAN_BUFFER value but no luck

Thanks and regards,

Neeraj Dhekale

[Kenneth]

Hi,

Have you tried setting a breakpoint in the NRF_BLE_SCAN_EVT_NOT_FOUND to check the content of p_data from a debugger? Alternatively, can you copy the content of p_data to a static array before outputting?

Kenneth

[Neeraj Dhekale]

Hi Kenneth 

Thank you so much for your reply.

I have tried to check but the length itself is showing 30.

And also tried the approach of the static array but no luck

Thanks and regards,

Neeraj Dhekale

[Kenneth]

Hello,

If you download the ibeacon specification:
https://developer.apple.com/ibeacon/ 

You can find that the advertisment packet should be 30bytes (see Table 2-1 in the spec document). 

So I am starting to think that part of the raw data you see here is not the advertisment packet, but the scan response packet (which should not be enabled by the ibeacon spec, but maybe they have anways). 

Best regards,
Kenneth

[Neeraj Dhekale]

Hello Kenneth

But here my question is if the nrfConnect app is able to get all these raw data without any connection to the beacon. why not our nrf52840 able to give?

Also, I have confirmed that ESP32 (Espressif using getPayload() function) controller also gives the complete raw data, unlike nrf52840.

Thanks and regards,

Neeraj Dhekale

[Kenneth]

Neeraj Dhekale said:

But here my question is if the nrfConnect app is able to get all these raw data without any connection to the beacon.

You don't need a connection, however it's likely the raw data is split into two packets here.

For a central device you can on the BLE_GAP_EVT_ADV_REPORT event check the p_ble_evt->evt.gap_evt.params.adv_report.type.scan_response field if the received packet is a scan response or not. When starting scanning you need to set the scan_params.active=1 to request scan response packets before calling sd_ble_gap_scan_start().

So, can you check if you get the remaing data in the scan_response?

Best regards,
Kenneth

[Neeraj Dhekale]

Hello Kenneth 

I have tried the way you suggested but getting the same result not getting the remaining data.

Thanks and regards,

Neeraj Dhekale

[Kenneth]

Please make an on-air sniffer log so I can see the actual data on-air here:
https://www.nordicsemi.com/Products/Development-tools/nrf-sniffer-for-bluetooth-le 
(direct link: https://infocenter.nordicsemi.com/pdf/nRF_Sniffer_BLE_UG_v4.1.x.pdf) 

Kenneth

[Neeraj Dhekale]

Hello Kenneth 

Kenneth said:

it's likely the raw data is split into two packets here.

I think you are right. I have tried to display only GAP_AD_TYPE during BLE scan and it seems that it is getting called 2 times in the same milliseconds. In below image you may see {1}  {ff} received first and the {a} {16} {9} received right after 1st data received. That means ble_evt_handler() function is getting called twice everytime.

Is there any option to get all in once. I have already set scan_params.active=1; or somewhere by setting in sdk_config.h file?

So due to this I need to save it somewhere all these GAP_AD_TYPE and then I need to pass it to ble_advdata_parse() function to get all raw data like show in the above nRF connect screenshot (1st main question of this thread)..

Thanks and regards,

Neeraj Dhekale

[Kenneth]

You are on the right track here, so you need to buffer that packets somehow if you need to parse both the advertisment and scan response to check for data.

Kenneth