Question about the CRC for nrf_802154_transmit_raw

[Glen M]

Hi,

I'm working on a product using an nRF52840 that must communicate with a custom 802.15.4 product created by my customer. Their product does something nonstandard - after they apply their upper layer AES-128 encryption, they throw out the encrypted CRC and instead insert the original unencrypted CRC in its place. They use this value as a part of the Initial Vector to decrypt the packet.

I'm using NCS/zephyr version 2.0.0.

In looking at the documentation for nrf_802154_transmit_raw function in nrf_802154.h, it says "The CRC is computed automatically by the radio hardware. Therefore, the FCS field can contain any bytes".

Does that mean that I won't be able to overwrite the CRC with my own value?

Do you know what CRC algorithm is used?

Thanks,

Glen

[JONATHAN LL]

Hi,

It will be calculated based on what is in CRCCNF, CRCPOLY and CRCINIT

see https://infocenter.nordicsemi.com/topic/ps_nrf52840/radio.html?cp=4_0_0_5_19_11_4#ieee802154_crc

Regards,
Jonathan