Rockwell Jupiter GPS receiver

Last update: 21-Oct-2010 23:44 UTC

Synopsis

Address: 127.127.31.u
Reference ID: GPS
Driver ID: JUPITER
Serial Port: /dev/gpsu;  9600 baud, 8-bits, no parity.

Description

This driver supports at least some models of the Rockwell Jupiter GPS receivers (Jupiter 11, Jupiter-T), they must at least support the Zodiac Binary Protocol.

The driver requires a standard PPS interface for the pulse-per-second output from the receiver. The serial data stream alone does not provide precision time stamps, whereas the PPS output is precise down to 40 ns (1 sigma) for the Jupiter 11 and 25 ns (1 sigma) for Jupiter-T according to the documentation. If you do not have the PPS signal available, then you should probably not be using the Jupiter receiver as a time source. This driver requires a PPS signal and the time output from Jupiter receivers is not predictable in NMEA mode; the reported time can take one second steps.

Monitor Data

The driver always puts a lot of useful information on the clockstats file, and when run with debugging can be quite chatty on stdout. When first starting to use the driver you should definitely review the information written to the clockstats file to verify that the driver is running correctly.

Fudge Factors

time1 time

Specifies the time offset calibration factor, in seconds and fraction, with default 0.0.

time2 time

Not used by this driver. Should be left at zero.

stratum number

Specifies the driver stratum, in decimal from 0 to 15, with default 0.

refid string

Specifies the driver reference identifier, an ASCII string from one to four characters, with default GPS.

flag1 0 | 1

Not used by this driver.

flag2 0 | 1

Specifies the mobility of the GPS receiver: 0 for walking (default), 1 for driving.

flag3 0 | 1

Specifies the PPS signal on-time edge: 0 for assert (default), 1 for clear.

flag4 0 | 1

Not used by this driver.

Additional Information

The driver was resurrected from a sorry state using the Windows NT port and a Jupiter 11, and has since seen little testing on other platforms. On Windows there exist a barrier though, as there is no publicly available PPSAPI implementation, at least not to my knowledge. However, there has been one success report using Linux 2.4.20 and PPSkit 2.1.1.

The Jupiter receivers seem to have quite a few names. They are referred to at least as Rockwell receivers, Navman receivers, Zodiac receivers, Conexant receivers and SiRF Technology receivers. Rockwell seems to be the original and most commonly used name and Navman seems to be the current supplier.

Configuration

The edge of the PPS signal that is `on-time' can be set with flag2. There is currently no way to cause the PPS signal to control the kernel PLL.

Performance

The performance is largely unexplored. I have achieved submillisecond stability using a Jupiter 11, but the poor result is more than likely due to the proprietary PPSAPI implementation or Windows itself.

This driver does not handle leap seconds.