nrf52840 RADIO_MODE_MODE_Ble_LR125Kbit

[Ellison]

// CRC Config
    NRF_RADIO->CRCCNF = (RADIO_CRCCNF_LEN_Three << RADIO_CRCCNF_LEN_Pos); // Number of checksum bits
    if ((NRF_RADIO->CRCCNF & RADIO_CRCCNF_LEN_Msk) == (RADIO_CRCCNF_LEN_Two << RADIO_CRCCNF_LEN_Pos))
    {
        NRF_RADIO->CRCINIT = 0xFFFFUL;   // Initial value
        NRF_RADIO->CRCPOLY = 0x11021UL;  // CRC poly: x^16 + x^12^x^5 + 1
    }
    else if ((NRF_RADIO->CRCCNF & RADIO_CRCCNF_LEN_Msk) == (RADIO_CRCCNF_LEN_One << RADIO_CRCCNF_LEN_Pos))
    {
        NRF_RADIO->CRCINIT = 0xFFUL;   // Initial value
        NRF_RADIO->CRCPOLY = 0x107UL;  // CRC poly: x^8 + x^2^x^1 + 1
    }
    else if ((NRF_RADIO->CRCCNF & RADIO_CRCCNF_LEN_Msk) == (RADIO_CRCCNF_LEN_Three << RADIO_CRCCNF_LEN_Pos))
    {
        NRF_RADIO->CRCINIT = 0xFFFFFFUL;   // Initial value
        NRF_RADIO->CRCPOLY = 0x107UL;  // CRC poly: x^8 + x^2^x^1 + 1
    }

How should the CRCINIT and CRCPOLY be set?

Thanks

[Susheel Nuguru]

I am not an expert in the selection of polynomial for the packets but i can dig a bit more if needed. But before that, could i ask you what you are attempting to do?

Are you designing your own BLE stack on nRF52840? if so, why?

[Ellison]

hi,

Sorry for replying so late. Yes, I want to use the mode LR_125Kbit on NRF52840. The CRC check of this mode only supports Radio_CRCCNF_LEN_THREE, but I know how to set it CRC.

Thanks and Best regards.

[Dmitry]

Hi,

CRC parameters are the same for 1M and LR125. For BLE advertising channel, here is the right setup of CRC:

NRF_RADIO->CRCCNF  = (RADIO_CRCCNF_LEN_Three << RADIO_CRCCNF_LEN_Pos) | 
                       (RADIO_CRCCNF_SKIPADDR_Skip << RADIO_CRCCNF_SKIPADDR_Pos); // Skip Address when computing crc     
  NRF_RADIO->CRCINIT = 0x555555;    // Initial value of CRC
  NRF_RADIO->CRCPOLY = 0x00065B;    // CRC polynomial function

For data channel, CRCINIT is passed in CONNECT_IND message. If you are implementing some custom protocol, you're on your own.

[Ellison]

Thank you very much for your help.

Can I ask you another question?For 1M and LR125K, whether there is a big difference in the communication distance, LR125K will be much farther.I haven't tested this.

Thanks and Best regards.

[Dmitry]

You can look at this blog to estimate the difference, but it's better to make your own tests because results may vary in different conditions.