Low level 802.15.4 transmit code

RE: Low level 802.15.4 transmit code

DU_Radio — Fri, 20 Jun 2025 13:35:08 GMT

I have found the problem, it is a combination of two issues. 1. The code as written relies on an interrupt from the radio to clear a transmit flag. There are some rare cases where this interrupt is lost and the flag is never cleared. 2. The radio does indeed need full re-initialization in some cases but this is even rarer than #1.

Statistics: 700,000 messages, 1 reset needed, then a thunderstorm blew through and in 500,000 messages, 14 resets were needed. With a code change that clears the interrupt flag, and only resets of that did not work: 1,099,000 messages, flag cleared 6 times, reset once. I believe this resolves the issue.

Thank you for your help.

RE: Low level 802.15.4 transmit code

DU_Radio — Tue, 17 Jun 2025 12:34:40 GMT

In the4 second test it ran for 102,643 messages, then failed the CCA_busy. I had it do a radio_set_sniff() which initializes all the radio registers the same as powerup, but that did not recover. It does not hang, just always fails the CCA_busy.

while (!NRF_RADIO->EVENTS_CCAIDLE && !NRF_RADIO->EVENTS_CCABUSY && !sig_ccabusy && --timeout);

Clearly the channel is not 100% busy for hours so is there another reset sequence that I should use?

RE: Low level 802.15.4 transmit code

hmolesworth — Tue, 17 Jun 2025 00:15:57 GMT

I suggest adding a --timeout check to every while(..); instead of just a few of those; on timeout reset RADIO and start again. For example all whiles of the form:

    while (!NRF_RADIO->EVENTS_READY);

Most of us learn to adopt such defensive programming practices when dealing with hardware registers and devices which misbehave when least expected ..

RE: Low level 802.15.4 transmit code

DU_Radio — Mon, 16 Jun 2025 23:57:17 GMT

Susheel,

Thanks for the changes, they made a huge difference. It runs for over 100K message, but then stops and fails the CCA forever after. Is this a case where a full register-reload is needed? I am testing that now. Is it possible that some external event getting into the receiver, e.g. lightning, might flip a bit and require a register reload?

Darryl

RE: Low level 802.15.4 transmit code

Susheel Nuguru — Mon, 09 Jun 2025 07:38:53 GMT

I am no expert in this and also do not think that there is any flowchart readily available so I will try to write a template code for the suggestions I have provided below

Can you please modify your radio_send_custom in your radio.cpp as below

void radio_send_custom(uint8_t *pBuffer, uint8_t channel) {

  /* No shortcuts on disable. */
  NRF_RADIO->SHORTS = 0x0;

  /* Switch radio to TX. */
  radio_disable();

  for (size_t try_ = 0; try_ < MAX_RETRIES; try_++) 
  {
    /* Switch packet buffer to tx_buffer. */
    NRF_RADIO->PACKETPTR = (uint32_t)pBuffer;
    NRF_RADIO->INTENSET = (1 << RADIO_INTENSET_END_Pos);
    NVIC_ClearPendingIRQ(RADIO_IRQn);
    NVIC_EnableIRQ(RADIO_IRQn);

    NRF_RADIO->EVENTS_READY = 0;
    NRF_RADIO->TASKS_RXEN = 1;
    Serial.write("While 1 ");
    while (!NRF_RADIO->EVENTS_READY);

    NRF_RADIO->EVENTS_CCAIDLE = 0;
    NRF_RADIO->EVENTS_CCABUSY = 0;
    sig_ccabusy = false;
    NRF_RADIO->TASKS_CCASTART = 1;

    Serial.write("While 2 ");
    int timeout = 10000;
    while (!NRF_RADIO->EVENTS_CCAIDLE && !NRF_RADIO->EVENTS_CCABUSY && !sig_ccabusy && --timeout);
    Serial.write("While 3 ");

    if (timeout == 0 || sig_ccabusy || NRF_RADIO->EVENTS_CCABUSY) 
    {
      Serial.println("WARNING: retry for CCABUSY");
      sig_ccabusy = false;
      radio_disable();
      delay(100);
      continue;
    }

    NRF_RADIO->TXPOWER =
        (RADIO_TXPOWER_TXPOWER_Pos4dBm << RADIO_TXPOWER_TXPOWER_Pos);
    NRF_RADIO->FREQUENCY = channel_to_freq(channel);

    NRF_RADIO->EVENTS_DISABLED = 0;
    NRF_RADIO->TASKS_DISABLE = 1;
    while (!NRF_RADIO->EVENTS_DISABLED);

    NRF_RADIO->EVENTS_READY = 0;
    NRF_RADIO->TASKS_TXEN = 1;
    Serial.write("While 4\r\n");
    while (!NRF_RADIO->EVENTS_READY);
    NRF_RADIO->TASKS_START = 1;
    return;
  }

  Serial.println("ERROR: retry too many times");
}

Also ensure CCAIDLE and CCABUSY are cleared in the IRQ handler RADIO_IRQHandler

if (NRF_RADIO->EVENTS_CCABUSY) {
  NRF_RADIO->EVENTS_CCABUSY = 0;
  NRF_RADIO->TASKS_DISABLE = 1;
  while (!NRF_RADIO->EVENTS_DISABLED);
  sig_ccabusy = true;
}

if (NRF_RADIO->EVENTS_CCAIDLE) {
  NRF_RADIO->EVENTS_CCAIDLE = 0;
  sig_ccabusy = false;
}

RE: Low level 802.15.4 transmit code

DU_Radio — Thu, 05 Jun 2025 03:53:05 GMT

Do you have perhaps, a detailed flowchart of how to configure and operate the radio? Or perhaps someone who could correct the rather simple low-level radio software that I attached? Only radio.c access the hardware. The project can be build with Arduino 1.8 IDE, most college engineering students could handle that. Or are you suggesting that Nordic has lost the tribal knowledge to run their own hardware?

RE: Low level 802.15.4 transmit code

Susheel Nuguru — Tue, 03 Jun 2025 08:38:12 GMT

So DU_Radio,

We unfortunately do not have that as we are working with nRF Connect SDK now.

RE: Low level 802.15.4 transmit code

DU_Radio — Tue, 03 Jun 2025 03:12:10 GMT

Susheel,

If you have any low level transmit example code in C, for any platform, that would likely provide the quickest solution. There was some on the Nordic site at one time but it seems to have been taken down some years ago.

RE: Low level 802.15.4 transmit code

DU_Radio — Tue, 03 Jun 2025 02:03:27 GMT

Susheel,

Thank you for your advice on CCA cleanup. Does it need a full powerup init (and if so why?) or just the CCA threshold and clear events and re-enable the tasks? I ask because a full powerup init when CCA_IDLE was false did not help.

The code has most of the constants from the original GIT repo (not my project), these are the register addresses in the nRFD52840 datasheet so I thought they would be more meaningfull to the Nordic hardware folks. Also I was trying to avlod introducing more problems by incorrectly editing the register references. Yes it is certainly ugly. Once it is working I will do a major code cleanup.

Since this is a Nordic radio issue and not related to the platform it was built on, is there another forum that would be better suited to troubleshooting the radio?

Darryl

RE: Low level 802.15.4 transmit code

Susheel Nuguru — Mon, 02 Jun 2025 11:08:47 GMT

Hi DU_radio,

The repo looks lt uses PlatformIO and the API is a unknow to me. It is hard for us to review something that is using external SDKs, too many unknows to properly give you a proper debugging direction.

Regarding the radio handling, I can say one thing that you did not seem to have handled failed CCA scenario properly, it is wise to do a cleanup, deinit and reinit in that case. Also there are a lot of hardcoded values in your code, not very pleasant to read or review. I suggest you take this question to a proper forum API you are using here to implement this.

RE: Low level 802.15.4 transmit code

DU_Radio — Sat, 31 May 2025 04:25:55 GMT

My uploaded files went to some bit bucket. Here is the cleaned up code (3 files):

//Raw802.ino
#include <Arduino.h>
#include <stdint.h>
//#include <stdbool.h>
#include "radio.h"
#include <nrf52840.h>
#include <Adafruit_TinyUSB.h>// Seems to need this without Serial or USB. Maybe DFU boot loader needs it?

#define PIN_LEDX 22 // Red LED

// channel 
#define DEFAULT_INITIAL_CHANNEL 19

// read buffer  
uint8_t *rx_buffer;
uint8_t u8SeqNum = 0;
// the frame length in phy layer header 
uint8_t pkt_len = 0;
uint8_t u8PktBuf[100];

// has data transmitting
uint8_t bTransmitting = false;

// packets
#define MAX_PKTS_IN 12 // Maximum packets in the queue
struct __attribute__((packed)) packets_structure
{
  uint16_t size[MAX_PKTS_IN] = {0};
  uint8_t *pkt_buffer[MAX_PKTS_IN];
  uint8_t head = 0;
  uint8_t tail = 0;
} packets;

// channel
uint8_t radio_channel = DEFAULT_INITIAL_CHANNEL;


/**
 * nRF51822 RADIO handler.
 *
 * This handler is called whenever a RADIO event occurs (IRQ).
 **/
extern "C" void RADIO_IRQHandler(void)
{
  // if (NRF_RADIO->EVENTS_FRAMESTART)
  if (*(uint32_t *)(0x40001138)) //Events-FrameStart
  {
    *(uint32_t *)(0x40001138) = 0;
  }

  if (NRF_RADIO->EVENTS_READY)
  {
    NRF_RADIO->EVENTS_READY = 0;
    NRF_RADIO->TASKS_START = 1;
  }

  if (NRF_RADIO->EVENTS_END)
  {
    NRF_RADIO->EVENTS_END = 0;
    // NRF_RADIO->TASKS_START = 1;
    // If transmitt end
    if (bTransmitting)
    {
      bTransmitting = false;
      //Serial.write("SENDED ");
       //radio_tx_to_rx();
      //return;// maybe interrupt needs special return?
      goto exit;
    }
  }
  if (*(uint32_t *)(0x40001148))//CCA-Busy
  {
    Serial.println("CCABUSY");
    *(uint32_t *)(0x40001148) = 0;
    NRF_RADIO->TASKS_DISABLE = 1;
    while (NRF_RADIO->EVENTS_DISABLED == 0);
    //Serial.println("CCABUSY: disable the radio");
    sig_ccabusy = true;
  }
  if (*(uint32_t *)(0x4000114C))
  {
    Serial.println("CCASTOPPED");
  }
  if (*(uint32_t *)(0x40001144))//CCA-IDLE
  {
    Serial.println("CCAIDLE");
    sig_ccabusy = false;
    *(uint32_t *)(0x40001144) = 0;
    // NRF_RADIO->TASKS_CCASTART = 0
    //*(uint32_t *)(0x4000102c) = 1;
  }
  exit:
  {
  
  }
}

void setup()
{
  pinMode(LED_BUILTIN, OUTPUT);
  pinMode(PIN_LEDX, OUTPUT); // Going for the RED Led now
  Serial.begin(115200);
  rx_buffer = (uint8_t *)malloc(IEEE802154_FRAME_LEN_MAX + 3);

  radio_set_sniff(radio_channel, 0); // Setup the radio
}

uint32_t ctr = 0;
void loop()
{
  if (NRF_RADIO->EVENTS_READY)
  {
    NRF_RADIO->EVENTS_READY = 0;
    // NRF_RADIO->TASKS_START;
  }
  delay(1);
  ctr++;
  if(ctr > 900)// Transmit every 200mS
  {
    ctr = 0;
    pkt_len = 17; 
    memcpy(u8PktBuf, "\x11\x00\x00\x00\x11\x22\x33\x44\x55\x66\x77\x88\x99\xaa\xbb\xcc\xdd\xee\xff",19);
    u8PktBuf[3] = u8SeqNum++;
  }


  // memcpy pkt_buffer to tx_buffer
  if (!bTransmitting && pkt_len)
  {
    Serial.write(".");
    digitalWrite(PIN_LEDX, HIGH);
    bTransmitting = true;
    radio_send_custom(u8PktBuf, radio_channel);
    pkt_len = 0;
    digitalWrite(PIN_LEDX, LOW);
  }
}

//radio.cpp
#include "radio.h"
#include <Arduino.h>
#include <assert.h>

// signal for CCABUSY
volatile uint8_t sig_ccabusy = false;

/**
 * channel_to_freq(int channel)
 *
 * Convert a BLE channel number into the corresponding frequency offset
 * for the nRF51822.
 **/
uint8_t channel_to_freq(int channel) {
  assert(channel > 10);
  assert(channel < 27);
  return 5 * (channel - 10);
}

/**
 * radio_disable()
 *
 * Disable the radio.
 **/

void radio_disable(void) {
  if (NRF_RADIO->STATE > 0) {
    NVIC_DisableIRQ(RADIO_IRQn);

    NRF_RADIO->EVENTS_DISABLED = 0;
    NRF_RADIO->TASKS_DISABLE = 1;
    while (NRF_RADIO->EVENTS_DISABLED == 0);
  }
}

/**
 * @brief   Convert from dBm to the internal representation, when the
 *          radio operates as a IEEE802.15.4 transceiver.
 */
static inline uint8_t _dbm_to_ieee802154_hwval(int8_t dbm) {
  return ((dbm - ED_RSSIOFFS) / ED_RSSISCALE);
}

static int set_cca_threshold(int8_t threshold) {

  if (threshold < ED_RSSIOFFS) {
    return -1;
  }

  uint8_t hw_val = _dbm_to_ieee802154_hwval(threshold);

   NRF_RADIO->CCACTRL &= ~RADIO_CCACTRL_CCAEDTHRES_Msk;
  //*(uint32_t *)(0x4000166c) &= ~RADIO_CCACTRL_CCAEDTHRES_Msk;

   NRF_RADIO->CCACTRL |= hw_val << RADIO_CCACTRL_CCAEDTHRES_Pos;
  //*(uint32_t *)(0x4000166c) |= hw_val << RADIO_CCACTRL_CCAEDTHRES_Pos;
  return 0;
}

/**
 * radio_set_sniff(int channel)
 *
 * Configure the nRF51822 to sniff on a specific channel.
 **/

void radio_set_sniff(int channel, uint32_t access_address) {
  // Disable radio
  radio_disable();

  // Enable the High Frequency clock on the processor. This is a pre-requisite
  // for the RADIO module. Without this clock, no communication is possible.
  NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
  NRF_CLOCK->TASKS_HFCLKSTART = 1;
  while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0);

  // power should be one of: -30, -20, -16, -12, -8, -4, 0, 4
  NRF_RADIO->TXPOWER = RADIO_TXPOWER_TXPOWER_Neg20dBm;//Pos4dBm;
  NRF_RADIO->TXADDRESS = 0;

  /* Set 802154 data rate. */
  NRF_RADIO->MODE = RADIO_MODE_MODE_Ieee802154_250Kbit;
  /* Listen on channel . */
  NRF_RADIO->FREQUENCY = channel_to_freq(channel);

  /* set start frame delimiter */
   //NRF_RADIO->RESERVED12[4] = IEEE802154_SFD;// Gets a read-only error on ths
  *(uint32_t *)(0x40001660) = IEEE802154_SFD;

  /* set MHR filters */
   NRF_RADIO->MHRMATCHCONF = 0;         /* Search Pattern Configuration */
  //*(uint32_t *)(0x40001644) = 0;

   NRF_RADIO->MHRMATCHMAS = 0xff0007ff; /* Pattern mask */
  //*(uint32_t *)(0x40001648) = 0xff0007ff;

  /* and set some fitting configuration */
  NRF_RADIO->PCNF0 = ((8 << RADIO_PCNF0_LFLEN_Pos) |
                      (RADIO_PCNF0_PLEN_32bitZero << RADIO_PCNF0_PLEN_Pos) |
                      (RADIO_PCNF0_CRCINC_Include << RADIO_PCNF0_CRCINC_Pos));

  NRF_RADIO->PCNF1 = IEEE802154_FRAME_LEN_MAX;

  NRF_RADIO->MODECNF0 |=
      RADIO_MODECNF0_RU_Fast; // Enable fast mode for radio ramp up

  // Enable CRC
  NRF_RADIO->CRCCNF =
      ((RADIO_CRCCNF_LEN_Two << RADIO_CRCCNF_LEN_Pos) |
       (RADIO_CRCCNF_SKIPADDR_Ieee802154 << RADIO_CRCCNF_SKIPADDR_Pos));
  NRF_RADIO->CRCPOLY = 0x11021;
  NRF_RADIO->CRCINIT = 0;

  // DATAWHITE
  NRF_RADIO->DATAWHITEIV = 0x40;

  NRF_RADIO->PACKETPTR = (uint32_t)(rx_buffer);

  // configure CCA
  set_cca_threshold(CONFIG_IEEE802154_CCA_THRESH_DEFAULT);

  // Configure interrupts
  NRF_RADIO->INTENSET = RADIO_INTENSET_END_Msk | RADIO_INTENSET_FRAMESTART_Msk |
                        // RADIO_INTENSET_CCAIDLE_Msk |
                        RADIO_INTENSET_CCABUSY_Msk;
  // Enable NVIC Interrupt for Radio
  NVIC_SetPriority(RADIO_IRQn, IRQ_PRIORITY_LOW);
  NVIC_ClearPendingIRQ(RADIO_IRQn);
  NVIC_EnableIRQ(RADIO_IRQn);

  // Enable receiver hardware
  NRF_RADIO->EVENTS_READY = 0;
  NRF_RADIO->TASKS_RXEN = 1;
  while (NRF_RADIO->EVENTS_READY == 0);
  NRF_RADIO->EVENTS_END = 0;
  NRF_RADIO->TASKS_START = 1;
}

/**
 * Send raw data asynchronously.
 **/

void radio_send_custom(uint8_t *pBuffer, uint8_t channel) {

  /* No shortcuts on disable. */
  NRF_RADIO->SHORTS = 0x0;
  /* Switch radio to TX. */
  radio_disable();

  for (size_t try_ = 0; try_ < MAX_RETRIES; try_++) 
  {
    /* Switch packet buffer to tx_buffer. */
    NRF_RADIO->PACKETPTR = (uint32_t)pBuffer;
    NRF_RADIO->INTENSET = (1 << RADIO_INTENSET_END_Pos);
    NVIC_ClearPendingIRQ(RADIO_IRQn);
    NVIC_EnableIRQ(RADIO_IRQn);

    NRF_RADIO->EVENTS_READY = 0;
    NRF_RADIO->TASKS_RXEN = 1;
    Serial.write("While 1 ");// NEEDS THIS DELAY
    while (!NRF_RADIO->EVENTS_READY);

     NRF_RADIO->EVENTS_CCAIDLE = 0;
    //*(uint32_t *)(0x40001144) = 0;
    NRF_RADIO->TASKS_CCASTART = 1;
    //*(uint32_t *)(0x4000102c) = 1;

     Serial.write("While 2 "); // Needs this delay
    // while(!(NRF_RADIO->EVENTS_CCAIDLE || CCABUSY));
    while(!(NRF_RADIO->EVENTS_CCAIDLE || NRF_RADIO->EVENTS_CCABUSY));
    // wait for CCAIDLE or CCABUSY
    Serial.write("While 3 ");
    while (!(*(uint32_t *)(0x40001144) || sig_ccabusy));//CCA_IDLE
    if (sig_ccabusy) 
    {
      Serial.println("WARNING: retry for CCABUSY");
      sig_ccabusy = false;
      delay(100);
      continue;
    }

    /* Transmit with max power. */
    NRF_RADIO->TXPOWER =
        (RADIO_TXPOWER_TXPOWER_Pos4dBm << RADIO_TXPOWER_TXPOWER_Pos);
    NRF_RADIO->FREQUENCY = channel_to_freq(channel);

    // enable receiver
    NRF_RADIO->EVENTS_READY = 0;
    NRF_RADIO->TASKS_TXEN = 1;

     Serial.write("While 4\r\n");//needs this delay
    while (!NRF_RADIO->EVENTS_READY);
    NRF_RADIO->TASKS_START = 1;
    /* From now, radio will send data and notify the result to Radio_IRQHandler */
    return;
  }
  Serial.println("ERROR: retry too many times");
}

/**
 * Change radio from TX to RX, while keeping last configuration of
 *radio_send_custom or radio_set_sniff
 **/
void radio_tx_to_rx() {
  NRF_RADIO->PACKETPTR = (uint32_t)(rx_buffer);
  NVIC_DisableIRQ(RADIO_IRQn);
  NRF_RADIO->SHORTS = RADIO_SHORTS_READY_START_Msk;

  // NRF_RADIO->INTENSET = 0;
  NVIC_ClearPendingIRQ(RADIO_IRQn);
  NVIC_EnableIRQ(RADIO_IRQn);

  NRF_RADIO->EVENTS_DISABLED = 0;
  NRF_RADIO->TASKS_DISABLE = 1;

  while (NRF_RADIO->EVENTS_DISABLED == 0);

  NRF_RADIO->EVENTS_READY = 0;
  NRF_RADIO->TASKS_RXEN = 1;
}

//radio.h
/**
 * Radio module
 *
 * This module provides all the required functions to manage the nRF51822
 * transceiver.
 **/

#pragma once
#include <Arduino.h>

extern uint8_t *rx_buffer; /* Rx buffer used by RF to store packets. */

#define IRQ_PRIORITY_HIGHEST 0
#define IRQ_PRIORITY_HIGH 1
#define IRQ_PRIORITY_MEDIUM 2
#define IRQ_PRIORITY_LOW 3

#define RADIO_MODE_MODE_Ieee802154_250Kbit (15UL)


#define IEEE802154_FRAME_LEN_MAX (127U)   /**< maximum 802.15.4 frame length */
#define IEEE802154G_FRAME_LEN_MAX (2047U) /**< maximum 802.15.4g-2012 frame length */
#define IEEE802154_ACK_FRAME_LEN (5U)     /**< ACK frame length */
#define IEEE802154_FCS_LEN                  (2U)


#define RADIO_PCNF0_PLEN_32bitZero (2UL) /*!< 32-bit zero preamble - used for IEEE 802.15.4 */
#define RADIO_PCNF0_CRCINC_Include (1UL) /*!< LENGTH includes CRC */
#define RADIO_PCNF0_CRCINC_Pos (26UL) /*!< Position of CRCINC field. */
#define RADIO_CRCCNF_SKIPADDR_Ieee802154 (2UL) /*!< CRC calculation as per 802.15.4 standard. Starting at first byte after length field. */


#define RADIO_INTENSET_FRAMESTART_Pos (14UL) /*!< Position of FRAMESTART field. */
#define RADIO_INTENSET_FRAMESTART_Msk (0x1UL << RADIO_INTENSET_FRAMESTART_Pos) /*!< Bit mask of FRAMESTART field. */
#define RADIO_INTENSET_CCAIDLE_Pos (17UL) /*!< Position of CCAIDLE field. */
#define RADIO_INTENSET_CCAIDLE_Msk (0x1UL << RADIO_INTENSET_CCAIDLE_Pos) /*!< Bit mask of CCAIDLE field. */
#define RADIO_INTENSET_CCABUSY_Pos (18UL) /*!< Position of CCABUSY field. */
#define RADIO_INTENSET_CCABUSY_Msk (0x1UL << RADIO_INTENSET_CCABUSY_Pos) /*!< Bit mask of CCABUSY field. */


#define ED_RSSISCALE        (4U)    /**< RSSI scale for internal HW value */
#define ED_RSSIOFFS         (-92)   /**< RSSI offset for internal HW value */

/**
 * @brief IEEE802.15.4 default value for CCA threshold (in dBm)
 */
#ifndef CONFIG_IEEE802154_CCA_THRESH_DEFAULT
#define CONFIG_IEEE802154_CCA_THRESH_DEFAULT       (-70)
#endif

/* Bits 15..8 : CCA energy busy threshold. Used in all the CCA modes except CarrierMode. */
#define RADIO_CCACTRL_CCAEDTHRES_Pos (8UL) /*!< Position of CCAEDTHRES field. */
#define RADIO_CCACTRL_CCAEDTHRES_Msk (0xFFUL << RADIO_CCACTRL_CCAEDTHRES_Pos) /*!< Bit mask of CCAEDTHRES field. */

/**
 * @brief   Default start frame delimiter
 */
#define IEEE802154_SFD (0xa7)

// signal for CCABUSY
extern volatile uint8_t sig_ccabusy;
// max retries
#define MAX_RETRIES 5

// functions
uint8_t channel_to_freq(int channel);
void radio_disable(void);
void radio_set_sniff(int channel, uint32_t access_address);
void radio_send_custom(uint8_t *pBuffer, uint8_t channel);
void radio_tx_to_rx();