[time-nuts] How to get PPS from ublox mini-PCI GPS to APU2 SoC serial port for ntpd

STR . strykar at hotmail.com
Sun Aug 14 04:29:48 EDT 2016


What details would you like to know?

Serial port 3 and 4 are provided via the GPIO pins connected to an NCT5104D I/O controller which is 5V tolerant.
http://datasheet.octopart.com/NCT5104D-Nuvoton-datasheet-38893851.pdf
I believe that's why it was suggested to avoid the 3V-5V conversion.


-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Chris Albertson
Sent: Sunday, August 14, 2016 12:01 PM
To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
Subject: Re: [time-nuts] How to get PPS from ublox mini-PCI GPS to APU2 SoC serial port for ntpd

It looks like you would have to level-convert the 3 volt PPS to connect to
one of the GPIO pins.   It is easy to make a level converter with a FET or
you can buy one for $3 from Adafruit or spark fun.    As for the serial
data, that will be easy as there seems to be a 3 volt serial port.

The direct connection that was suggested might work or might not it depends on some details we don't know.

Seems like a good low power embedded PC.   Very much over kill for just
running NTP but I assume this will do other things too.

On Sat, Aug 13, 2016 at 7:32 PM, STR . <strykar at hotmail.com> wrote:

> Hi,
>
>
>
> I recently bought 2 ublox PCI-5S mini-PCI GPS modules and have ordered 
> a PCengines APU2C4 board I hope to install it in.
>
> Others have found it can provide PPS output http://emerythacks.blogspot.
> in/2013/01/u-blox-pci-5s-cheap-gps-module-for-your.html
>
>
>
> This is the x-64 AMD SoC by PCengines - 
> http://www.pcengines.ch/apu2c4.htm
>
> Schematics - http://www.pcengines.ch/schema/apu2c.pdf
>
> User manual (Page 8 has a nice overview of the board) - 
> http://www.pcengines.ch/pdf/apu2.pdf
>
>
>
> I would like to install and power the GPS from the mini-PCI slot and 
> output PPS directly on to one of the serial ports on the SoC board for ntpd.
>
> Since mini-PCI uses  3.3V and serial uses 5V I guess, I'm not sure how 
> to achieve this and am concerned I might fry the board.
>
>
>
> Do I need a MAX 232 voltage converter?
>
> Can this be done using the mini-PCI slot for power?
>
>
>
> I have posted my issue on the PCengines forum and got 1 response so 
> far that suggested I connect to COM3 on the GPIO header  -
>
> http://www.pcengines.info/forums/?page=post&id=B4D54F22-
> 8224-4A67-9F9E-85F988A1F888&fid=DF5ACB70-99C4-4C61-AFA6-4C0E0DB05B2A
>
> I'm not sure where exactly, these are the GPIO pins on the board 
> http://imgur.com/a/bAZLb
>
>
>
> When someone says "LPC serial IRQ and system interrupt latency will 
> add up to noticeable jitter" does that mean the jitter would be 
> equally bad from any serial port on the board or just from the 3rd serial off the GPIO pins?
>
> Here, someone else claims the PPS should have less jitter in a similar 
> setup - http://pcengines.info/forums/?page=post&id=CD275C4D-8050-
> 408A-BD16-6F50468C74C2
>
>
>
> I'm hoping someone here could help me out with this as I'm well in 
> over my head by now.
>
>
>
>
>
>
>
> Cheers,
>
> S
>
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>



-- 

Chris Albertson
Redondo Beach, California
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