[ntp:questions] GPS clock for Linux

Uwe Klein uwe_klein_habertwedt at t-online.de
Mon Sep 15 15:23:40 UTC 2008


Martin Burnicki wrote:

> So the behaviour should depend on the implementation of an individual
> converter type. BTW, similar problems arise with serial-to-LAN converters
> which redirect a serial data stream using IP packets.

I have used the standard pl2303 type converters
and their bastard brethren ( to make an
existing RS485 based daisychained system "USB ready" )

communication to this system was a fast chitchat @38400 Baud:

every second {
	foreach slot_used {
		send <STX><BoxAddr><SlotAddr><payload message with linefeed>,
		wait for response including linefeed,
		send <ETX>  // to deselect the current slot
	}
}

~30 slots used.
I never had any latency problems.

Thus my guess is that these latency may lie in the firmware running
on the sirf chipset.

the gpsd people seem to have delved into this too:
	http://gpsd.berlios.de/performance.html

Q: does the sirf chipset talk on its own or do you have to request
sentences?
( the gpsd article gives the impression that its query .. response )


uwe




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