Hi Folks, I have been posting to the NTP 'questions mailing' list regarding modification of NMEA refclock driver. The current driver implementation supports 4800 baudrate, GPGGA, GPGLL and GPRMC sentences.
We are using Accord's GPS Clock which generates NMEA sentences at 9600B. It also generates 1PPS and a custom NMEA sentence with GPS time-stamp. I've done few modifications to interface this with NTP. 1. Support for 4800 and 9600 2. Parsing of custom NMEA sentence After going through the NMEA ref.clock driver, it seems that the original author has choosen values 0(GPXXX), 1(GPRMC), 2(GPGGA) and 4(GPGLL) for mode field so that multiple sentences can be selected. As posted earlier reg. using the mode byte /field to support Accord GPS Clock, fourth bit cannot be used to denote the baudrate. Fourth bit can denote GPZDG(8) (custom NMEA format) while the fifth bit can be used for baudrate 0(4800) and 1(9600). But in this case multiple sentences may be allowed only if the value of last four bits is less than 8, because GPZDG gives GPS time and not UTC like rest of them. So if GPZDG is selected, others sentences should not be selected. I need comments and suggestions from folks who have been maintaining reference clock drivers regarding the suggested changes and its implications if any. Venu _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
