GPS system to linux ?

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GPS system to linux ?

Postby alx5962 » June 25th, 2011, 3:41 am

Hi,

I have an old GPS system that I don't use anymore and so I'd like to hack it to make it run linux.
All I know is that's a 200Mhz CPU and it's running Windows CE .NET 4.2 core. Here is the motherboard :

Image

Do you think it would be possible to run Linux on it ?
I tried to search more infos about this hardware on google, but had no luck (most was in chinese unluckily).

Thanks a lot !
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Re: GPS system to linux ?

Postby GaspingSpark » June 25th, 2011, 6:40 am

Yes, it is possible to run Linux on it. It's just an ARM system on a chip (otherwise Windows CE .Net wouldn't run). However, how much time are you willing to put into it?

Centrality Communications was bought out by SiRF which was bought out by some hacker-unfriendly scumbags named CSR (Cambridge Silicon Radio).

http://www.csr.com/

Here is the Non-Disclosure Agreement you must agree to before you can see any documentation:

http://www.csrsupport.com/nda.php

You're not going to be able to agree to that if you are developing open-source code. And it is possible they don't even have documentation for the old Centrality chips anyway.

That leaves reverse engineering of the existing firmware as your only option. This has been done a number of times for various PDA's and mobile phones running windows mobile, so the tools and knowledge are out there. It is just a time-consuming process.
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Re: GPS system to linux ?

Postby alx5962 » June 26th, 2011, 2:35 am

thank you very much for those informations !
So I guess it's no worth to work on porting linux to this system if I have to reverse engineering it.
Anyway, thank you again for those precious informations.
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Re: GPS system to linux ?

Postby nes » June 26th, 2011, 7:59 am

In your photo it looks like the GPS radio is a separate module connected via the grey wires to the top left. You could try probing those wires to work out the pin out and then you might be able to reuse that module in something else.

As there are four wires, these are quite likely to be: GND, Power, UART Tx, UART Rx.

The computer supplies power to the radio, but you need to check the voltage (+3.3V normally, but could be +2.5V). Ground can be found by testing for continuity between the metal can and one of the pins.

The UART is likely to transmit NMEA sentences in n-8-1 serial format. If you work out which of the two remaining pins is more active when the GPS is turned on, or which is active for a short burst once per second, you could try connecting it to the serial port of a PC via a transistor inverter. Run a terminal program and try different baud rates until you see something beginning "$GPRMC," appearing regularly.

Once you have the baud rate, connect your inverter to the last remaining pin and capture any data the GPS computer sends to the radio after a reset. If there is anything, you will probably want to copy that and send the same data at start up.

Now you can remove the radio module from the GPS, supply it with a regulated power supply and connect the UART pins to a serial port on your computer and make a GPS enabled thing. Even when indoors, a GPS receiver will give you atomic precision time. When outside, as well as position it will also give you your speed in knots (or km/h if you see the $GPVTG sentences) and your heading in degrees and may tell you other useful info too.
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Re: GPS system to linux ?

Postby alx5962 » June 26th, 2011, 8:09 am

that's a good idea, I may use the GPS receiver with an Arduino board :D
There's 5 wires connected to the GPS module so I guess further investigation is needed.
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Re: GPS system to linux ?

Postby MS3FGX » June 26th, 2011, 8:32 pm

Gotta love it when they put useful little bits like that on their own daughter boards. If only they could all be that simple...
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