Re: [tinydtls-dev] handshake message not received due to long processing

["Jan Kuehn" <kuehnj@xxxxxxxxxxxxxxxxxxxxxxxxxx>]

Hi Raul,

> One question, before applying the possible solutions, when you are having this
> scenario, the  server  sent multiple Hello Verify Request meanwhile the client is
> processing the messages?  This only to try to see a relation to the issues I was
> having with Contiki.

I'm not sure anymore if I ever saw multiple Hello Verify Request messages as I had a lot of different scenarios depending on how many debugging messages I had and how long the retransmit time was. Right now my setup is quite messy because I hacked at lot of different things: retransmit time, amount of debugging messages, disabled some ecc functions, even a little delay when sending packages. I actually just got a complete handshake working but this is far away from a good solution. I hope when I clean up my code and use the ecc hardware it will run again.

So I'm sorry that I cannot give you anything precise right now... However I definitely saw some messages being sent multiple times. But that was only when I used the radio autoack, so this is not related to the dtls retransmit. Is this in anyway close to the issues you had?

> By the way, sadly, what you describe is the current limitation of the motes, not
> something that  relies only in TinyDTLS, although as Olef already stated, moving
> to the micro-ECC could helps a lot.

You're right, the slow ecc implementation is definitely a problem but at first I noticed the package loss before any ecc functions where used. The problem there was that I had so many debugging messages which then blocked the receiving. As Olaf said this is due to the cooperative threading. But I also think that it's a problem of the cc2538 radio implementation. It should be possible for the radio to move the data out of the buffer in the receive interrupt. I'm not sure how other motes handle this issue.

Regards,
Jan