[Tinyos-help] serial send acknowledgement

David Moss dmm at rincon.com
Wed Feb 20 09:23:29 PST 2008


There's another aspect to consider here as well:  uC-to-uC serial
communications.  Although I haven't looked into it much deeper, I suspect
TinyOS's asymmetric serial acknowledgments could be playing a part in the
failures we've seen in preliminary attempts to get uC's to talk through
their serial stacks.

-David



-----Original Message-----
From: tinyos-help-bounces at millennium.berkeley.edu
[mailto:tinyos-help-bounces at millennium.berkeley.edu] On Behalf Of Philip
Levis
Sent: Wednesday, February 20, 2008 9:40 AM
To: Kaan Tuna
Cc: tinyos-help at millennium.berkeley.edu
Subject: Re: [Tinyos-help] serial send acknowledgement


On Feb 20, 2008, at 7:37 AM, Kaan Tuna wrote:

> Hello all,
> When we send data over the serial port, how can we verify that the  
> receiver (PC, terminal...) succesfully received the packet?
> Do we need a modification in the application layer (ie in the code,  
> SerialSend.SendDone ?)? Is there any implementation of this kind?

Yes. You need a modification in the application layer.

This has been a point of discussion on TEP 113. Currently, TinyOS  
acknowledges packets from the PC, but the PC does not acknowledge  
packets from TinyOS. The protocol would allow such a thing -- just  
send PROTO_PACKET_ACK to the PC -- but the serial stack  
implementation doesn't support it. On one hand, it would be nice if  
you could request ACKs; on the other, I'm worried about code bloat.  
Right now the serial stack is about 3.5-4K of code all together, and  
adding acks would probably add another 1K or so. Given that it's an  
infrequent request, yet many applications run into the code size  
limits on telos-family motes, I'm leery of adding support. Writing an  
alternative stack that supports acks isn't appealing, either, as that  
means maintaining parallel implementations (and I already maintain  
too much).

Phil
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