Wasif: Regarding setting the backoff values to 1us in the cc2420x stack: this clearly doesn't work, because the code would schedule an alarm 1us in the future, which is simply not possible. By the time the operation of scheduling the alarm completes, that time instant is going to be in the past, and the alarm will fire after the counter overflows and reaches that particular value again. To put it in another way: backoff values under (approximately) 200 microseconds are not valid.
To get rid of CSMA logic altogether, you need to remove the collision avoidance layer altogether and rewire the stack (CC2420XRadioC.nc) as I have described in my previous email. Janos On Wed, Jan 9, 2013 at 5:31 AM, wasif masood <[email protected]> wrote: > > Hi all, > > I am trying to measure the message delay on Telosb platform and now > comparing the CC2420 stack with CC2420X stack. Below are the two Histograms > showing the delay spread of Cc2420 and CC2420X stacks respectively. The > experiment is perfromed for around 1 hr at the same time using two > different frequency channels. > For CC2420X I have used the TimeSyncAMSend<TMicro,uint32_t> interface and > have calculated the delay at the receiver end as > > delay = call LocalTimeMicro.get() - call TimeSyncPacket.eventTime(msg) > > and for CC2420 Stack, I have used TimeSyncAMSend with Milli sec precision > and have calculated the delay as : > > delay = call LocalTimeMilli.get() - call TimeSyncPacket.eventTime(msg) > > in case of CC2420 stack CCA is disabled and for CC2420X stack, I have > changed RandomCollisionConfig implementatoin in CC2420XRadioP module in > such a way that all types of backoff values ( Initial, minimum and > congestion) are now just RADIO_ALARM_MICROSEC value (because I couldn't > find a direct way to disable it). > > Now, what I observe is a bit interesting since the two histograms show a > completely different delay behaviors, ie. with the Cc2420X stack the delay > ranges between 1 to 13ms, but with CC2420X stack the delay goes from 70ms > to 150ms. Is this also what any of you experience or is there something I > am missing here? > > here are the histograms: > > http://s14.postimage.org/55bs7ni0x/Telosb_CC2420x.png > > http://s8.postimage.org/8paur8s6d/Telosb_CC2420.png > > > Regards, > Wasif Masood > > _______________________________________________ > Tinyos-help mailing list > [email protected] > https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help >
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