Large packets failed when running at subGHz

[jeremy-ang]

We have discovered some problems with large ping packets when running at subGHz (920MHz).

Large ping tests with 2.4GHz :-

• Up to 1220 bytes (for non-secure mode)
• Up to 1200 bytes (for level 7 secure mode)

Large ping tests with subGHz (920MHz) :-

• Up to 636 bytes only (for non-secure mode)
• Up to 500 bytes only (for level 7 secure mode)

When testing large ping packets running at subGH, there are a bunch of error messages from serial radio.

For example, if we ping the the subGHz node with ‘ping -s 800 xxxx::xxxx:xxxx:xxxx:xxxx’, the ping failed and we see a bunch of error messages as shown in the image attached.

Seems like the large packet fix to support packet size up to 1280 bytes from Niclas only work for 2.4GHz but not for subGHz.

[jeremy-ang]

Adding delay between large pings solved the problem with up to 1224 bytes in subghz which is the same as 2.4GHz without LLSEC enabled. But with LLSEC (level 7) enabled, subghz only able to support up to 985 bytes with pings whereas 2.4GHz is able to support up to 1200 bytes. I guess the additional time taken to encrypt/decrypt the packet data and slower data rate in subghz causes this issue.