[opendtv] Re: A full explanation of the PSIP time issue.

John, I think you've so over-thought this that you've tied it in knots. I know about THIS much (holding two fingers tightly together) of PSIP, but it seems perfectly clear to me. You transmit GPS time and the correction factor, and the RECEIVER deals with the rest. YOUR side (the transmit side) seems pretty straightforward. It's the receiver side that's required to manage the details. The correction factor is a simple variable. If you want to know UTC time, you subtract the variable. EPG data must be in GPS seconds since any calculations to UTC time occurs in the receiver. If YOU are doing the calculation on the transmit side, the receiver calculations will lead to incorrect results. 


On 24-May-07, at 7:33 PM, johnwillkie wrote:




Paul Freeman wrote: (in part)
I>f anyone has Mark Eyer’s PSIP book “PSIP: Program and System Information Protocol”, they can see an example of how time in the STT is represented on page 150 at the bottom of the page. The following few >lines of text are from Mark’s example: 



>    Current time of day (UTC): 1:00 P.M., December 30, 2001;
You mean Mark Eyer started out calculating the value for a system time table using UTC?!, and didn’t make any correction to make it GPS?! Surely he understands that you can make the calculation just using GPS time values! (more likely he knows that the GPS to UTC conversion ahead of the time difference calculation is in elegant and would needlessly complicate the text.) 



And, he denoted the time span value as a count of GPS seconds!
In other words forks, he has somehow ended up with that same erroneous “beliefs” as mine. (Actually, at best, I travel in his wake.)
Do you think I should call Mark up and tell him that three people on this list don’t agree with his calculations and he needs “reeducation” as do I? Or would an email be more appropriate? Should we ask the publisher to withdraw the faulty text? Should we also have the spec withdrawn as faulty?
Should I refer this matter to T3/S8? What happens if Mark thinks it’s absurd? Since he’s T3/s8 chair, I could join ATSC, become a T3/s8 member and work to topple him as chair, then I could get Bert on T3/s8, and he could fix everything. 



  J



John Willkie
P.S. I might have to take back “EITs being in GPS time.” That’s from an informative portion of the text, and is contradicted by the plain language in the main body. Looks like I’ve found another nit to add to the list. 



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