Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPSdecoding cards

2017-02-22 Thread Bob Camp
Hi > On Feb 21, 2017, at 9:50 PM, Trevor N. wrote: > > On Tue, 21 Feb 2017 07:37:34 -0500, BC wrote: >> >> Some 1588 chip sets have (or had, I haven’t looked recently) external sync >> pins. >> This does get into the whole, what’s a motherboard / what’s a peripheral >>

Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPSdecoding cards

2017-02-22 Thread Hal Murray
q...@comcast.net said: > I found while looking at the datasheets for newer Intel server ethernet > cards that they have the ability to timestamp GPIO pin transitions, but none > of them have their internal timebase synchronized to a counter in the CPU. > It looks like they are clocked from a

Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPSdecoding cards

2017-02-21 Thread Trevor N .
On Tue, 21 Feb 2017 07:37:34 -0500, BC wrote: > >Some 1588 chip sets have (or had, I haven’t looked recently) external sync >pins. >This does get into the whole, what’s a motherboard / what’s a peripheral >debate. Plugging in a 1588 card to get that pin probably no longer counts >as a simple

Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPSdecoding cards

2017-02-21 Thread Bob Camp
Hi > On Feb 20, 2017, at 9:26 PM, Trevor N. wrote: > > SA6CID wrote: >> >> So, I thought actually of the jitter added on the way between our >> accurate source (GPS rx), until we can capture our timer. How much can >> this be? As far as I see we don't have a capture mode

Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPSdecoding cards

2017-02-20 Thread Trevor N .
SA6CID wrote: > >So, I thought actually of the jitter added on the way between our >accurate source (GPS rx), until we can capture our timer. How much can >this be? As far as I see we don't have a capture mode for the HPET. But, >if we have to do it in software, we get more than 100 ns jitter.

Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPSdecoding cards

2017-02-20 Thread Peter Monta
Time transfer over USB can be improved by timestamping on both ends, then using a robust estimator for the clock offset. For example, imagine the USB is a small microprocessor peripheral. It has a local timer, freely incrementing, based on its local clock. When it gets a USB interrupt from the

Re: [time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPSdecoding cards

2017-02-19 Thread David J Taylor
From: Chris Albertson [] What you care about is the uncertainty of this process NOT the offset but the standard deviation of the offset. .. and in the absence of numerical values of the SD, well-scaled graphs of offset can show the variation in offset quite well.