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

Scott Stobbe scott.j.stobbe at gmail.com
Tue Aug 23 15:03:27 UTC 2016


Certainly could work, I give the author credit for saving one gps module
from e-waste. Hopefully the USB drivers for the ublox module will provide a
virtual com port, then all you have to worry about is wiring the PPS line.

On Tue, Aug 23, 2016 at 2:40 AM, STR . <strykar at hotmail.com> wrote:

> Could another way be to cut out the mini-pci interface like
> http://galeria.tech-blog.pl/U-blox_PCI-5S_GPS/U-blox_PCI-5S_
> GPS_10.jpg.html though I'm not sure if he's driving it via serial?
>
>
> -----Original Message-----
> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Scott
> Stobbe
> Sent: Monday, August 22, 2016 10:46 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
>
> The mini-PCI Express Card specification includes quite a bit more than
> just a single PCI-Express lane, there is also provisions for I2C (smbus),
> USB, LEDs, SIM, etc... While without looking a the physical card or
> specification I can't be certain, but I highly doubt it implements a
> PCI-Express interface. It is surely just using the USB interface over the
> express card slot. The GPS card should enumerate over the USB bus without
> any issues. In windows, ublox should provide you with USB drivers for their
> modules.
>
> You will have to experiment to see if the RX/TX lines of the GPS module
> are active after a POR, or if it defaults to USB, as that is how it was
> intended to be used. But the PPS line definitely needs to be connected to
> one of modem control lines of a UART.
>
> On Sun, Aug 21, 2016 at 11:30 AM, STR . <strykar at hotmail.com> wrote:
>
> > Thank you!
> > Your post has made my choices clear, UART-c might be it!
> > A previous poster said there'd be no difference in jitter using any of
> > the
> > 4 COM ports and this was reassuring.
> > I will start studying the pinouts to confirm the pin numbers while I
> > wait for the null-modem cable to arrive.
> >
> > Another question, would connecting PPS, Tx/Rx to the GPIO pins on
> > UART-c make U-blox's Windows u-Center software see this as attached to
> > a physical serial port?
> > If not, how would I present the GPS to Windows via serial?
> > I'd like to test updating the firmware and it appears to not work via
> > a mini-pci to WWAN 3G USB adapter.
> >
> > Others have reported:
> > "After Emeryth published the pinout, I also started to experiment with
> > this board. I found out that you can update the firmware using the
> > LEA-5 firmware version 6.02 from the u-blox web site. The module also
> > works very well with the patched firmware version EXT_G50_602_LEA-5H.
> > bdbfccefb9dbd8395dec7adece53c1f9.bin. This version enables the output
> > of raw data for use with rtklib for real-time kinematic and precision
> > positioning.
> >
> > You can then use the standard drivers from the u-blox web site for
> > Windows. They provide a virtual COM port. Please note that updating
> > the firmware just worked using the physical serial port of the
> > Mini-PCIe card, it did not work using the USB adapter."
> >
> >
> >
> > -----Original Message-----
> > From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Paul
> > Sent: Tuesday, August 16, 2016 2:27 AM
> > 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
> >
> > On Mon, Aug 15, 2016 at 5:35 AM, STR . <strykar at hotmail.com> wrote:
> >
> > > Pardon my ignorance, I'm not sure what COM port the PPS is tied to
> > > or what you mean.
> >
> >
> > I think there's some confusion.
> >
> > Normally the PPS input to Linux (I'm not sure about FreeBSD) is tied
> > to the DCD pin in a serial port.  The PPS code is connected to the
> > interrupt from the DCD.  It can be tied to another pin (DSR or CTS I
> > forget), a parallel port or a GPIO pin (a la RaspberryPi or
> > BeagleBone).  Anything other than DCD normally requires a specific
> > kernel build.  The APU2c has an I/O part connected via an LPC bus.
> > It's essentially 4 UARTS.  UART-a is connected to a DE-9 connector via
> > a level shifter.  All signals are present.  UART-b is brought to J3
> > unshifted.  Even though J3 has five pins only transmit, receive and
> > ground are connected.  UARTs "c" and "d" are brought to J17 either as
> > 18 GPIO signals or 2x8 RS-232 signals (the latter requires
> > non-standard bios code to set up the chip).  So if we imagine that you
> > want to use the DCD pin on UART-c you'd configure the GPIO pins as
> > serial and connect to pin 9 on J17.  Be advised that the specifics in
> the previous may be wrong so check the schematic.
> >
> > Now if you want to read the correct time as a sentence from the GPS
> > you'd connect the Tx/Rx pins on your module to the corresponding pins
> > on a 3V3 serial port.  Continuing to use UART-c that would be pins 7 and
> 8 on J17.
> >
> > Now regarding jitter.  Pascal suggests that the jitter involved in
> > using his take on the LPC connected super i/o part might be too high.
> > As noted someone said that was the case with the APU1.  While I
> > wouldn't be surprised if that were still true with the APU2 you might
> > find the time "good enough".  Trust but verify.
> >
> > Finally, these boxes are intended to be routers (hence the three
> > network
> > interfaces) not time-servers and unless you're irrevocably wedded to
> > the miniPCIe in APU2 route there are probably better choices for time
> servers.
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