some one reply :(
On Mon, Sep 19, 2011 at 1:24 PM, Ambuj Varshney <[email protected]> wrote:
> Hi,
>
> I am working on project for which we need time synchronization with
> accuracies in range of 10-20 microsecond,we are using custom zigbit boards
> for this.
>
> I have tested FTSP protocol in range of milliseconds in a small single hop
> network with 6 nodes and I got mean absolute deviation to be close to 1 ms.
>
> However, since it has already been tested at level of accuracies of
> microsecond, I wanted to test this at precision of microseconds. I have made
> the following changes to include support for Microsecond level of
> synchronization in FTSP for Zigbit modules. ( I am using Internal RC
> oscillator and modules are running at 8MHz, this gives us Timer 3C to be
> roughly 1 MHz if prescaler of 8 is chosen)
>
> Similar to TimeSync32kC, I have defined TimeSyncMicroC :
>
> I have replaced occurrence of TMilli for precision with TMicro and I am
> using TimeSyncAMSendRadio instead of TimeSyncAMSendMilli, for local time I
> am using LocalTimeMicroC component and wiring it to LocalTime of TimeSyncP.
>
> LocalTimeMicroC is implemented like this :
>
> configuration LocalTimeMicroC
> {
> provides interface LocalTime<TMicro>;
> }
>
> implementation
> {
> components CounterThree16C;
> components new TransformCounterC(TMicro, uint32_t, TMicro,
> uint16_t, 0, uint32_t);
> components new CounterToLocalTimeC(TMicro);
>
> LocalTime = CounterToLocalTimeC;
> CounterToLocalTimeC.Counter -> TransformCounterC;
> TransformCounterC.CounterFrom -> CounterThree16C;
> }
>
> I have modified TestFtsp program to use TimeSyncMicroC component instead of
> TimeSyncC. I am using TIMESYNC_RATE of 1 seconds .
>
> However, when I run FtspDataLogger java application :
>
> It seems the nodes are getting synchronized , however,the global time
> stamps it seems are two decimal larger than what they should be, for
> instance when I switch on the nodes and after a second, when the global time
> stamp should be lets say 123456 microseconds, I am instead getting 12345678
> . There are two additional digits at the end. Is this because we don't
> exactly have 1Mhz and this represents fractional part? or is there anyother
> reason for this ?
>
> A Sample output ( Taken 10-15 seconds after switching on two nodes ):
>
> 1316289798632 1 10862 123875602 0
> 1316289798640 2 10862 123877248 0
> 1316289798876 1 10863 125779640 0
> 1316289798880 2 10863 125782999 0
> 1316289799116 2 10864 127696422 0
> 1316289799128 1 10864 127692081 0
> 1316289799364 1 10865 129618795 0
> 1316289799368 2 10865 129623388 0
> 1316289799608 1 10866 131552548 0
> 1316289799612 2 10866 131556963 0
> 1316289799852 1 10867 133461952 0
> 1316289799856 2 10867 133466610 0
> 1316289800096 1 10868 135392969 0
> 1316289800100 2 10868 135398599 0
> 1316289800344 1 10869 137331991 0
> 1316289800348 2 10869 137338190 0
> 1316289800588 1 10870 139256495 0
> 1316289800592 2 10870 139263078 0
> 1316289800828 1 10871 141149451 0
> 1316289800832 2 10871 141154505 0
> 1316289801072 1 10872 143077883 0
> 1316289801076 2 10872 143083971 0
> 1316289801316 1 10873 144992362 0
> 1316289801320 2 10873 144999012 0
> 1316289801564 1 10874 146945885 0
> 1316289801808 1 10875 148867941 0
> 1316289801812 2 10875 148874823 0
> 1316289802050 2 10876 150790668 0
> 1316289802059 1 10876 150784937 0
>
> Also if we discard last two digits, and assume the rest to be microsecond
> representation of when the broad-casted message was received ( Beaconing
> rate 250ms) by node, the errors it seems is more than few microseconds,
> which I assume is because of using Internal RC oscillator and not external
> crystal to maintain time and problem with stability. is there anything I can
> do to improve this ? as zigbit modules have not exposed pin of Atmega1281
> for having external crystal to drive MCU clock or 32KHz crystal to maintain
> time.
>
>
> Thanks,
> Ambuj Varshney
> Research Engineer
> Embedded systems and Wireless Sensor Group
> DAIICT, India
>
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