> On 10/7/06, Chris Kuethe <[EMAIL PROTECTED]> wrote: > > usb gps receivers don't usually have any sort of PPS signal which is > > what this code depends on. > > > > CK > As I understand it, ntpd uses a timedelta sensor to make adjustments > to the clock. If nmeaattach properly creates a timedelta sensor (and > it does because I have one that properly shows my offset) then this > should work. ntpd doesn't know anything about my gps receiver it only > knows that there is a timedelta sensor on my computer. That's at least > how I understand it.
That is correct. You plug a GPS receiver into a serial port, or into a USB port which makes it come up as a serial port. But it is just some random device on a serial port. We don't know that there is a GPS on that particular serial port. But you do -- so you run the nmeaattach, indicating the serial port that the GPS is on. nmeaattach tells the kernel to 'intercept' the data on that particular serial port. If the kernel code notices that the little bytes flowing by look like the GPS NMEA protocol, then the kernel creates a timedelta sensor. Every once in a while, ntpd checks to see if any new timedelta sensors have showed up (or, likewise, if any have gone away). And ntpd uses their value as an offset against true time.
