[Tinyos-devel] Time Sync Requirements

[Matt Welsh]

Apart from this we need to be very mindful of memory requirements for  
storing values of that size. I don't want every TOS_Msg to be tagged  
with an extraneous 8 bytes that I'm not going to use.

Further, there are few reasons to believe that a mote-class device  
needs to track time (of any granularity, nanosecond or otherwise) with  
a 64-bit "dynamic range". Most of the time we only care about relative  
time, not absolute time, at least on the mote level: a base station  
can readily map relative times back to their absolute representations.

64 bits of nanoseconds is more than 584 years. Once we have sensor  
networks with deployments approaching that duration then I'll be the  
first to put this proposal back on the table.




On Dec 19, 2007, at 6:05 PM, David Gay wrote:

> On Dec 19, 2007 2:53 PM, Michael Newman <mnewman at dragonnorth.com>  
> wrote:
>> I think a 64
>> bit representation can be good enough to handle all of the  
>> interesting cases
>> including date/time and sub-nanosecond time counting. Note that  
>> there are
>> two types of time represented by 64 bit numbers, elapsed time and  
>> date/time.
>> Elapsed times can be added to date/times. Elapsed times might be  
>> logged in
>> smaller sized datums if they happen to fit. Date/times can not be  
>> shrunk
>> without adding complexity.
>
> There's a practical problem: msp430-gcc's 64-bit support is reportedly
> broken(*). Until someone in the TinyOS community (or outside...)
> actually decides to spend the time to fix this, 64-bit types in TinyOS
> will be impractical.
>
> David Gay
> *: Yes, this is regrettable and all that. But regrets don't fix
> compiler bugs or magically make alternative compilers
> available/affordable.
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