Hal Murray wrote:
I started collecting low cost GPS receivers a year or two ago. I thought I had some with the SiRF-II chips. Either I can't find them or I didn't actually get any.
I've been "collecting" the OEM modules for about the same amount of time. That said, I haven't got that many -- a pair of Trimble SVeeSixes with 4.12 firmware and an Axiom Sandpiper (SiRF2 based). I've just got a pair of Fastrax "iTrax" IT321 receivers, which are surface-mount (i.e. solder-down to a PCB) receiver modules based on the SiRF3 chipset.
GSW3.2.4_3.1.00.12-SDK003P1.00a GlobalSat BU-353 GSW3.2.2_3.1.00.12-SDK003P1.01a AmbiCom GPS-USB Rev 2.1 GSW3.2.2_3.1.00.12-SDK003P1.01a Navibe GM-720 GSW3.2.4Pat2_3.1.00.12-SDK001P1.00 Navisys GR-300
All of which are running the SiRF 3.2 firmware, so if there is a firmware bug in play, they're all going to be doing much the same thing...
They all use the Prolific PL2303 serial-to-USB chip.
That might be what's causing the timing jitter, especially if there are other devices on the USB bus. USB-to-serial chips aren't known for accurate timing -- a few of them buffer incoming data and then send it over the USB bus in one burst.
That's not to say the SiRF chipset isn't the cause of the error, but it might not be the only variable. I'd be tempted to tie a TTL=>RS232 level translator to the RXD_IN pin on the PL2303, then connect the output of the translator to a spare 'proper' RS232 port on a PC. The timing should be far more accurate (though probably not fantastic).
-- Phil. li...@philpem.me.uk http://www.philpem.me.uk/ _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
