Radio configure as Rx with 802.15.4 mode receives more than 127 bytes

Question

Hi all,

I'm working with the reception of 802.15.4 packets on nRF52840 for which I have configure the radio as follows:

//PHR length in bits
#define PACKET_LENGTH_FIELD_SIZE  (8UL) 
//Max ota frame size for O-QPSK modulation
#define MAX_OTA_FRAME_SIZE            127

//Buffer for frames to be received: 127 MAX PSDU size + PHR size
static uint8_t  radioPacketBuffer[MAX_OTA_FRAME_SIZE + 1];   

void RADIO_IRQHandler(void)
{
    //Is the radio ready
    if(NRF_RADIO->EVENTS_READY == 1U)
    {
      NRF_RADIO->EVENTS_READY = 0;

      NRF_RADIO->EVENTS_END = 0U;
      // Start listening and wait for end of reception event
      NRF_RADIO->TASKS_START = 1U;
    }

    if(NRF_RADIO->EVENTS_END == 1U)
    {
      NRF_RADIO->EVENTS_END = 0;
      //Get the timestamp
      NRF_TIMER1->TASKS_CAPTURE[0] = 1;
      //Check if the checksum is correct
      if (NRF_RADIO->CRCSTATUS == 1U)
      {
        OTAFrameValidReceivedFlag = true;
      }
      StartRxRadioFlag = true;
    }
}

void radioInit(void)
{
    // Set radio configuration parameters
    NRF_RADIO->SHORTS = 0;   
    NRF_RADIO->TXPOWER = 0;
    NRF_RADIO->MODE      = (RADIO_MODE_MODE_Ieee802154_250Kbit << RADIO_MODE_MODE_Pos);

    // Packet configuration
    NRF_RADIO->PCNF0 = (PACKET_LENGTH_FIELD_SIZE << RADIO_PCNF0_LFLEN_Pos)    |
                       (RADIO_PCNF0_CRCINC_Include << RADIO_PCNF0_CRCINC_Pos) |  
                       (RADIO_PCNF0_PLEN_32bitZero << RADIO_PCNF0_PLEN_Pos) ; 

    // Packet configuration
    NRF_RADIO->PCNF1 = MAX_OTA_FRAME_SIZE;

    // Radio address config
    NRF_RADIO->BASE0 = 0;
    NRF_RADIO->BASE1 = 0;
    NRF_RADIO->PREFIX0 = 0;
    NRF_RADIO->PREFIX1 = 0;

    // CRC Config
    NRF_RADIO->CRCCNF = (RADIO_CRCCNF_LEN_Two << RADIO_CRCCNF_LEN_Pos)  |
                        (RADIO_CRCCNF_SKIPADDR_Ieee802154 << RADIO_CRCCNF_SKIPADDR_Pos); // Number of checksum bits

    NRF_RADIO->CRCINIT = 0;          // Initial value
    NRF_RADIO->CRCPOLY = 0x11021UL;  // CRC poly: x^16 + x^12^x^5 + 1


    NRF_RADIO->TIFS = 0;
    //NRF_RADIO->DATAWHITEIV = 0x40;  
    NRF_RADIO->BCC = 0x18;            
    NRF_RADIO->DACNF = 0;
    NRF_RADIO->MHRMATCHCONF = 0;          //This was taken from ZR on running state, not really sure what it does... nrf spec does not provide help about it...
    NRF_RADIO->MHRMATCHMAS = 0xff000700;  //This was taken from ZR on running state, not really sure what it does... nrf spec does not provide help about it...
    
    NRF_RADIO->MODECNF0 = (RADIO_MODECNF0_RU_Fast << RADIO_MODECNF0_RU_Pos)   |
                          (RADIO_MODECNF0_DTX_Center << RADIO_MODECNF0_DTX_Pos);

    //802.15.4 configration
    NRF_RADIO->SFD = 0xA7;
    NRF_RADIO->EDCNT = 0;
    NRF_RADIO->EDSAMPLE = 0;
    NRF_RADIO->CCACTRL = 0x02141400;  //From ZR configuration...
    NRF_RADIO->POWER = 1;
    
    NRF_RADIO->PACKETPTR = (uint32_t)&radioPacketBuffer;
    NRF_RADIO->FREQUENCY = 5UL;    



    NRF_RADIO->INTENSET = RADIO_INTENSET_READY_Enabled << RADIO_INTENSET_READY_Pos | 
                          RADIO_INTENSET_END_Enabled << RADIO_INTENSET_END_Pos;
    
    NVIC_SetPriority(RADIO_IRQn, 1);
    NVIC_ClearPendingIRQ(RADIO_IRQn);
    NVIC_EnableIRQ(RADIO_IRQn);
}

In the application loop we have:

      if(OTAFrameValidReceivedFlag)
      {
        timestamp = NRF_TIMER1->CC[0];
        OTAFrameValidReceivedFlag = false;

        /*  ...
        
        SOME CODE THAT PROCESS THE CONTENT OF radioPacketBuffer
        
        ... */
        
        memset(radioPacketBuffer,0,sizeof(radioPacketBuffer));
        
        //valid frame received!
        bsp_board_led_invert(0);
      }
      if(radioActive & StartRxRadioFlag)
      {
        // Start listening again
        NRF_RADIO->TASKS_START = 1U;
      }

we receive frames and transmit frames properly, but there is sometimes in which we receive frames in radioPacketBuffer, which payload is bigger than 127, this is readed in radioPacketBuffer[0].

According to 802.15.4 for O-QPSK the max payload is 127 bytes, all the frames we received seems fine, but as soon we start capturing on populated networks we see this kind of behavior which is causing the device to fail.

Has this happened to anyone?, do we have a wrong configuration to capture packets?