Re: GPS reciever for cubetruck

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Sun, Jun 21, 2020 at 07:59:16PM +0200, Ede Wolf wrote:
> Hi,
> 
> thanks very much for your pentiful answers. Indeed, that PPS thing opend a
> new can of worms, as I've always thought of getting one of those OXCO
> Disciplined Oscillators, but eventually never really could part with the
> money.
> I still would like to be able to provide the nmea data via network to other
> clients, so gpsd support would still be on the wishlist.
> 
> However, searching for gps mouses that explicitly advertise PPS and linux
> support was harder that I've assumed. Assuming, if there is linux support,
> they will run most likely with NetBSD as well.
> 
> As for the Venus8 chips, I have found a german article, that uses exactly
> one of those chips for ntp using pps. However, in the comments section of
> amazon for that gps mouse someone claimed, that pps is not available. Makes
> one wonder.
> 
> The ready to use u-blox 8 available here are rather expensive, and mostly
> from navilock.
> 
> Something like this:
> 
> https://www.navilock.de/produkt/62576/merkmale.html?setLanguage=en
> 
> which leads to the next question, however slightly off topic:
> 
> Like the Microstack recommended earlier this thread by Mr. Bouyer, I have
> seen a couple of recievers, usually for arduino, that have a 5 pin
> connection. Next to powersupply and your transmit/recieve, there also exists
> a dedicated pps pin. However, I have not been able to find out, what pin on
> a RS232 connector this should go to. And if in genereal those are suitable
> for direct RS232 connection anyway or wether buffers are needed.

This is likely a 3.3 or 5V TTL serial port interface. For RS232 you'll
need buffers (like a max232 chip).
However, AFAIK the cubietruck doesn't have a RS232 serial port either,
but also has GPIOs that can be remapped to a serial port, so it will
interface directly with a 3.3V TTL serial port.

the PPS pin could be connected to an interrupt pin, or the DTR pin of
the serial port. But I've not done it, the timing of the serial port
is more than enough for my need, I don't need sub-second precision :)

AFAIK the cubietruck uses a A20 SoC, the same as on the Olimex lime2 board
I used for my project.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--