Re: [gpsd-dev] Parallel build broken?

[Paul Fertser]

Hi,

On Sun, Nov 24, 2013 at 11:39:35PM -0800, Gary E. Miller wrote:
> Paul Fertser <address@hidden> wrote:
> > One possible universal measure would be to mark the time as inaccurate
> > until after, say, 25 minutes (2x full almanac transmission interval to
> > improve robustness) 
> > doesn't require knowing current GPS-UTC value at all.
> 
> 2x a full almanac is 4 hours.  Some parts of the almanac are only sent once
> every two hours.

[1] (listed as a reference on Wikipedia) disagrees (quote from
wikipedia, the content matches [1] but is more condensed):

Each GPS satellite continuously broadcasts a navigation message on L1
C/A and L2 P/Y frequencies at a rate of 50 bits per second (see
bitrate). Each complete message takes 750 seconds (12 1/2 minutes) to
complete. The message structure has a basic format of a 1500-bit-long
frame made up of five subframes, each subframe being 300 bits (6
seconds) long. Subframes 4 and 5 are subcommutated 25 times each, so
that a complete data message requires the transmission of 25 full
frames. Each subframe consists of ten words, each 30 bits long. Thus,
with 300 bits in a subframe times 5 subframes in a frame times 25
frames in a message, each message is 37,500 bits long. At a
transmission rate of 50 bit/s, this gives 750 seconds to transmit an
entire almanac message. Each 30-second frame begins precisely on the
minute or half-minute as indicated by the atomic clock on each
satellite.

[1] http://gpsinformation.net/gpssignal.htm

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