Re: [gpsd-dev] Trimble tweaks (parity, time offset)

[Oliver Jowett]

On 5 January 2016 at 08:58, Eric <address@hidden> wrote:

Oliver Jowett <address@hidden>:

>
> What do I need to do to get these patches integrated into the main tree?

I'll take the FIXED_PARITY patch right away if you'll email it to me.

Ok, I'll find some time to clean that up and send it on.

> (on a slightly related topic, I couldn't get the hunt loop to work
> usefully; how fast is this meant to converge? it was taking minutes per
> speed setting..)

That varies for reasons I don't understand and which seem to relate to
quirks in the OS tty layer. It's very fast under Linux, we typically
get sync in less than a second and the worst I've seen is around three
seconds.  It's slower on BSDs.

This is on Linux (specifically, on a Raspberry Pi talking to the Trimble via a CP2105 usb-serial port) but it was still taking minutes.

When I looked at it briefly the problem seemed to be that the hunt loop would only advance after seeing this many bytes (or reads? I'm not clear, I didn't dig too far) from the serial device:

#define SNIFF_RETRIES   (MAX_PACKET_LENGTH + 128)

which is quite a large value (644?) and if you are on the wrong baud rate then you might only be seeing 5-10 bytes per second so it takes ages.

It seems like there should be a realtime timeout here too, so the hunt loop advances if it hasn't seen a valid packet within a couple of seconds.

Oliver