[Tinyos-devel] ctp vs other radio clients

[Omprakash Gnawali]

On Mon, Oct 27, 2008 at 6:28 PM, Philip Levis <pal at cs.stanford.edu> wrote:
>
> 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.
>
> Hrm. That's weird. Please read TEP 116: send should  return EBUSY iff
> it has returned SUCCESS to a prior call and has not yet signaled
> sendDone.
>
> This suggests that it's a bug in CTP where it calls send multiple times.

Is it possible that the busy state is stack-wide rather than per type
in the implementation of tep116? Is there one instance of StateC for
CC2420 stack (UniqueSendC.nc) ?

- om_p