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

[Jørgen Holmefjord]

The parameter MAX_PACKET_SIZE is set to 127 by default in the nRF IEEE 802.15.4. Radio Driver, and this is set in the radio peripheral during init procedure.

Is the nRF only transmitting, or also receiving? Is it reception on the TI side that is poor when payload is high? Could you provide a sniffer trace of what is happening on-air with larger payloads? You can use our 802.15.4 sniffer solution if you do not have specialized equipment for this.

[Ted Herman]

I was unable to get the standard rx example to work, using the 802.15.4 git repo (https://github.com/NordicSemiconductor/nRF-IEEE-802.15.4-radio-driver) of  Tue Feb 12 2019 (c0114b43bb222f55c5d4b22d4d144210df4cb1cc). However I was able to run the rx example using an early version of the same repo, from commit d049e668a055d114f956fd389349cd3f16b99399, Date: Wed Nov 14 2018. Here is sample output below. Two packets are shown, one from the Nordix tx demo, the other from a cc2531 device, and the total packet length exceeds 32 - so I think this is working properly. I am uncertain why, with the newest version of the 802.15.4 driver, that the rx program does not work. I had to make some minimal changes in the Makefile due to changes in the stack, otherwise it seems the same. 

<info> app: Packet
<info> app:  27 41 88 35 22 00 FF FF|'A.5"...
<info> app:  01 00 3F 06 02 02 03 04|..?.....
<info> app:  05 06 07 08 09 0A 0B 0C|........
<info> app:  0D 0E 0F 10 11 12 13 14|........
<info> app:  15 16 17 18 19 1A 41 00|......A.
<info> app:  00 00 00 00            |....    
<info> app: Packet
<info> app:  1D 41 98 31 32 33 34 35|.A.12345
<info> app:  36 37 38 39 3A 3B 3C 3D|6789:;<=
<info> app:  3E 3F 40 41 42 43 44 45|>?@ABCDE
<info> app:  46 47 48 49 23 00 00 00|FGHI#...
<info> app:  00 00 00 00 00 00 00 00|........
<info> app:  00 00 00 00            |....    

[Jørgen Holmefjord]

I will try to reproduce this behavior, and check with the developer what is happening, if I'm able to reproduce it.

[Ted Herman]

I have made some progress on this, and will update status I hope in one more day.

[Ted Herman]

I rewrote my testing program carefully preparing the sdk_config.h and Makefile. Now it runs with the latest Nordic 802.15.4 git repo. When I use two nRF52840 dev boards, packets can be larger without error between xmit and recv, though I did not test very large (127 byte) packets. However, the problem of interoperation remains, packets larger than 29-32 bytes, depending how things are counted, likely get CRC errors or frame truncation. Not all packets fail, just the majority. This occurs only in the nRF -> cc2531 direction. I do not have RF equipment to check further. 

[awneil]

Have you tested the "large" packets between two CC2531s ... ?

[Ted Herman]

Yes, I have tested this in the past with reasonable results. My plan next is to get several CC2531s and repeat the test, in case the one I have been using is poor hardware.

[Ted Herman]

I tried with a few different CC2531s, and there does seem to be a hardware or software problem, though details are unclear so far.