802.15.4 Packet Size

[Ted Herman]

Hello,

I've been testing 802.15.4 single PHY (no softdevice) and analyzing packets on a TI CC2531, just to check interoperability. Things seem to work well when the packet size is at most 29 bytes. When I increase the packet size to 30 or more, the packet reception is poor (maybe some packets get through, many get CRC errors). I had thought that the limitation was 127 bytes for the 802.15.4 standard. 

In a way, 29 bytes makes sense: considering the first byte (not in the packet) is the length, then the two auto-generated CRC bytes as the footer, we get the magic number of 32 bytes. Is that what's going on, 32 bytes is the actual limit?

Thanks,

Ted 

[Jørgen Holmefjord]

Hi,

Can you post the code you use on the nRF side? The specifications have defined a maximum payload of 127, but the radio on either of the ends could limit this number. 

Best regards,
Jørgen

[Ted Herman]

OK, this is the code which I modify for experimenting on the nRF side.

---

#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>

#include "nrf_802154.h"
#include "boards.h"
#include "nrf_delay.h"
#include "IEEE802154.h"

#define MAX_MESSAGE_SIZE 29 
#define CHANNEL 26
#define PACKET_MAX_PAYLOAD 18

typedef uint16_t mac_addr_t;
struct motepacket {
  uint8_t length;
  uint16_t fcf;
  uint8_t data_seq_no;
  mac_addr_t pan;
  mac_addr_t dest;
  mac_addr_t src;
  uint8_t iframe;    // field for 6lowpan, is 0x3f for TinyOS
  uint8_t type;
  uint8_t data[PACKET_MAX_PAYLOAD];
  uint8_t fcs[2];    // will become CRC, don't count this in length.
  };
typedef struct motepacket motepacket_t;

static volatile bool m_tx_in_progress;
static volatile bool m_tx_done;
uint8_t seqno = 0; 
uint8_t buffer[sizeof(motepacket_t)];
motepacket_t * p = (motepacket_t *)buffer;

//int main(int argc, char *argv[])
int main(void)
{
    bsp_board_init(BSP_INIT_LEDS);
    bsp_board_led_invert(0);

    p->fcf = 0x0000;
    // the following FCF lines are copied
    p->fcf &= 1 << IEEE154_FCF_ACK_REQ;
    p->fcf |= ( ( IEEE154_TYPE_DATA << IEEE154_FCF_FRAME_TYPE )
                  |  ( 1 << IEEE154_FCF_INTRAPAN )
                  |  ( IEEE154_ADDR_SHORT << IEEE154_FCF_DEST_ADDR_MODE )
                  |  ( IEEE154_ADDR_SHORT << IEEE154_FCF_SRC_ADDR_MODE ) );
    p->data_seq_no = 0;
    p->pan = 0x22;     // 
    p->dest = 0xFFFF;  //  
    p->src = 99;       //  
    p->iframe = 0x3f;  //  
    p->type = 0x37;    //  
    //p->length =  offsetof(motepacket_t,data) + PACKET_MAX_PAYLOAD - 1;
    p->length = 29;
    m_tx_in_progress = false;
    m_tx_done        = false;

    nrf_802154_init();
    nrf_802154_channel_set(CHANNEL);
    nrf_802154_receive();

    while (1)
    {
        p->data_seq_no = seqno++;
        for (int i=0; i<PACKET_MAX_PAYLOAD; i++) p->data[i] = seqno+i;
        bsp_board_led_invert(0);
        // if (m_tx_done)
        // {
        //     m_tx_in_progress = false;
        //     m_tx_done        = false;
        // }

        // if (!m_tx_in_progress)
        // {
            //tx_buffer_fill(message, sizeof(message));

            //m_tx_in_progress = nrf_802154_transmit(message, sizeof(message), true);
            m_tx_in_progress = nrf_802154_transmit_raw(buffer, true);
            if (m_tx_in_progress) {
                bsp_board_led_invert(1);
            }
        // }
        printf("sent msg\n");
        nrf_delay_ms(3000);

    }

    return 0;
}

void nrf_802154_transmitted(const uint8_t * p_frame, uint8_t * p_ack, uint8_t length, int8_t power, int8_t lqi)
{
    (void) p_frame;
    (void) length;
    (void) power;
    (void) lqi;

    m_tx_done = true;
             bsp_board_led_invert(2);

    if (p_ack != NULL)
    {
        //nrf_802154_buffer_free(p_ack);
        nrf_802154_buffer_free_raw(p_ack);
    }
}