I don't want to hijack Andrew's thread. Just wanted to add to Achim's comments about jitter and offset.
USB2 devices should accept polls every 125 microseconds. [My USB knowledge is limited.] I have two devices. One is the Navisys GR701 which I suspect you're familiar with; it is an integrated GPS + Serial->USB. The other is a Garmin LVC18x connected to a Sabrent USB 2 to serial cable. Both devices report having a PL2303. Both poll at 1 msec. The GR701 has a thin cable. The Sabrent USB->Serial has a thick cable. On Wed, Jul 8, 2020 at 6:53 PM Hal Murray <hmur...@megapathdsl.net> wrote: > > stevesommars...@gmail.com said: > > My RPi4 (Raspbian Buster) has a GPS+PPS/USB. Serial->USB uses Prolific > > PL2303, which supports USB 2.0 > > > which means 1 msec polling of the PPS signal. I've been unable to poll > more > > frequently > > As far as I know, the PL2303, 067b:2303, is an old/slow chip. (I forget > the > right magic USB terms) Why do you expect it to go faster than 1 ms? > > It and the FTDI chip(s) are popular and widely known to be well supported > on > Linux. I'll be very surprised if it goes faster. > > What sort of device are you using? One way to tell if it is likely to go > faster than 1 ms is the thickness of the wire. Faster speeds need more > shielding for EMI reduction (or something like that) which turns into > fatter > cables. It's pretty easy to tell if you have samples of both in front of > you. > I think you can only use the thinner cable if t runs at 1 ms and you hard > wire the chip to the end of the cable as is typical of a GPS mouse. > > > > -- > These are my opinions. I hate spam. > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.