Hi, I think software processing also need time. In CC2420TransmitP.nc, before transmission, TX data has to be loaded from ram to CC2420 through SPI bus, I think it's a time-consuming operation.
What's more, you can turned off radio backoff (through RadioBackoff interface provided by CC2420ActiveMessageC.nc) so as to get the exact time between a send request and a sendDone event. Also, if you want to test whether 250kbps could be reached, you can do as follows: a. Send an empty pkt and record the time *t1* between send request and sendDone event. b. Send a 80 bytes pkt and record the time *t2*. c. calc the bit rate = 80 * 8 / (t2 - t1), step a and b experience the same send process, so the difference is more exact. Best Regards, Ruitao Xu 在 2011年3月29日 上午1:02，蔡沅峰 <[email protected]>写道： > Dear all, > > > We have a high-data-rate application and we need to decrease the > transmission delay (between send.send and send.sendDone). > > The payload of our packet is 80 bytes. ( Total packet size is about 100 > bytes in Tinyos ) > > We've adjusted the initial backoff time defined in CC2420csmaP.nc to the > range of 10~60 ticks (under 32khz clock) > > The above two added is about 100*8/250(kbits/sec) + 35/32768 = 4.27ms > > But when we measure the time between send.send and send.sendDone, the > result is 7.82ms, much bigger than 4.27ms > > Even though we take the congestion backoff time into account( 10~80 ticks > ----> 45/32768 = 1.37ms ), the result is still less 7.82ms > > But the inteval between our testing data packest is 3 seconds, the > congestion backoff time shouldn't exist. > > Our application is broadcast, so we don't consider ACK wait time. > > Does anyone know why the larger transmission delay in our experiment? > > > We also record the time when the packet is send out ( by the SFD interrupt > ), the time between this SFD time and send.sendDone is about 1.99ms > > What confuse us is this time is much less than the data transmission needed > (4.27ms), does anyone know why? > > > Many thanks!! > > > Best regards, > > > Sean > > _______________________________________________ > Tinyos-help mailing list > [email protected] > https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help > -- Be Your Personal Best!
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