[Tinyos-devel] ctp vs other radio clients

[Philip Levis]

On Oct 27, 2008, at 5:36 PM, Branislav Kusy wrote:

> guys,
>
> is it allowed to use the radio (ie ActiveMessageC) while using Ctp? if
> not, should it be allowed? most of my applications require it...
>
> i couldn't find anything about this in tep123, but i found this  
> comment
> in CtpForwardingEngineP.nc,v1.17:
>
> line 487:
>       subsendResult = call SubSend.send(dest, qe->msg, payloadLen);
> ....
> lines 509-519:
>       else if (subsendResult == EBUSY) {
> 	// This shouldn't happen, as we sit on top of a client and
>         // control our own output; it means we're trying to
>         // double-send (bug). This means we expect a sendDone, so just
>         // wait for that: when the sendDone comes in,  we'll try
>         // sending this packet again.	
> 	dbg("Forwarder", "%s: subsend failed from EBUSY.\n", __FUNCTION__);
>         // send a debug message to the uart
>         call CollectionDebug.logEvent(NET_C_FE_SUBSEND_BUSY);
>       }
>
> if there are other radio clients, subsendResult may be EBUSY even if  
> we
> don't double send. therefore, we should just call
> 	startRetxmitTimer();
>
> if we don't do this, ctp basically hangs forever.
>
> i've had this problem for a long time - ctp hanging on me for no good
> reason. my test application can reproduce it in a few seconds. i  
> tested
> calling startRetxmitTimer() from the EBUSY case and it fixed the
> problem. i'm not sure if it didn't introduce any other problems,  
> though.


Sorry it took me so long. Finally got to this. Can you try this fix?

Change the line in Send.send that reads:

if (radioOn && !call RetxmitTimer.isRunning()) {

to

if (radioOn && !sending) {

I think the bug is that the Retxmit timer has fired, the event is a  
task on the queue, but the task calling Send is ahead of it. From the  
timer system's standpoint, the timer is no longer running, but...

That being said, I'm not able to recreate the hanging bug. But this  
logic makes it that EBUSY never occurs.

Phil