[time-nuts] TBolt: UTC PPS

[Tom Van Baak]

> I was close to typing in the same stuff.  I got:
>  -9.31323e-10 -5.32907e-15
> 
> In that packet, a0 is double precision.  Does anybody know why they need all 
> those bits?

Hal,

Referring to the GPS ICD, the size of A0 in subframe 4
is a signed scaled 32 bit integer so if a receiver chooses
to convert it to floating point it needs a double precision
format to contain it without loss of precision. A1, on the
other hand, is a signed scaled 24 bit integer and so it
just fits in a single precision floating point number. So
Trimble did the right thing here.

What's equally interesting is to look at the binary values
for A0 and A1 right now. |A0|, the time offset, ranges
from 0 to 2^31 scaled by 2^-30 seconds, or 0.931 ns to
2 seconds. |A1|, the frequency offset, ranges from 0 to
2^23 scaled by 2^-50, or 7.45e-9 to 8.88e-16.

Based on this we can tell the binary values for A0 and
A1 today are just 1 and 6. So while the range of these
two correction numbers is very wide; GPS is running
so close to UTC that it's at the extreme bottom end of
the resolution right now.

/tvb