Specify exact BLE advert packet bits in SW

RE: Specify exact BLE advert packet bits in SW

ytesfai — Tue, 11 Feb 2025 12:55:04 GMT

Hi Emil Lenngren , yes I agree - unfortunately I didn't include all the combinations I tried but I tried both with whitened access address (more in desperation) and with just PDU+CRC whitened. I also tried no pre-whitening and had the radio perform whitening.

RE: Specify exact BLE advert packet bits in SW

Emil Lenngren — Tue, 11 Feb 2025 12:46:01 GMT

You wrote "Whitened Adv Access Address (Whitened 0x8E89BED6)", but the access address is not part of the data that is whitened. Only the PDU+CRC is whitened. The whitening is performed after the CRC has been both calculated and appended to the PDU.

RE: Specify exact BLE advert packet bits in SW

ytesfai — Tue, 11 Feb 2025 12:35:00 GMT

Hi again,

I'm still stuck on this issue. I've tried various permutations of actual Base and Prefix registers to specify the access address, as well as header+PDU+CRC including inserting CRC from my code vs having the radio chip compute and insert the CRC block. I've also tried both pre-whitening the PDU+CRC in my application vs having the radio do the whitening and I still cannot receive the packet transmitted to be received by a BT sniffer. I suspect that I have:

- Bit ordering error
- Endianness issue
- Configuration issue
- Something else?

I received an email on 2/7 with the message that an Engineer has been assigned to look into this. Is this still the case? Any updates?

Thanks
Yohannes

RE: Specify exact BLE advert packet bits in SW

ytesfai — Fri, 07 Feb 2025 01:08:08 GMT

Emil Lenngren, hmolesworth thanks so much for the quick responses. I get now how to disable CRC as well as disable whitening in the radio and do both those in SW. So the composed packet I have now is:

[PREAMBLE (0xAA), Whitened Adv Access Address (Whitened 0x8E89BED6), Whitened PDU, Whitened CRC]

Then configure radio:

- RADIO_CRCCNF_LEN_Disabled (disable CRC)

- Set whiteen in nrf_radio_packet_conf_t to false (disable whitening)

I will try this and report back, but in the meantime any guidance you can provide from your experience would be great.

Thanks
Yohannes

RE: Specify exact BLE advert packet bits in SW

hmolesworth — Thu, 06 Feb 2025 22:29:35 GMT

You might find this discussion useful in addition to Emil's comments; I show a manually-constructed packet which is derived from multiple previous posts

radio-2-4ghz-length-field

RE: Specify exact BLE advert packet bits in SW

Emil Lenngren — Thu, 06 Feb 2025 22:24:09 GMT

If you read the specification at docs.nordicsemi.com/.../radio.html, you can see that it is possible to disable the crc and whitening in the corresponding configuration registers, but it's not possible to remove the preamble or access address. I think you need to set STATLEN to 3 if you want to send or receive the CRC raw.