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Developing custom firmware mods for (legacy) Forerunner 201

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  • Developing custom firmware mods for (legacy) Forerunner 201

    Hi Everyone!

    Unsure if this forum is the right place for this; please do let me know otherwise

    Wondering if it's possible to develop a coordinate convertor for the old Forerunner 201, to go from Lat./Long. to UTM NAD27 (at least). I received the FR201 as a gift a WHILE ago, and now hoping to be able to use it as a backup GPS while trekking as well. I know I should probably upgrade to a ForeTrex but curious if this creative experiment is possible. Full disclosure: I have no experience in app development. I'm familiar with the math behind the conversions and trying to gauge how easy it is to talk to the FR201 to upload custom firmware. I'd work with someone more experienced to create the actual app, if this is possible. I tried a cursory search on the forums but couldn't find anything for older units (I'll look again with different terms).

    Please let me know if there are any questions.


  • #2
    Thats not possible no. There are no compilers published for non connect iq devices.
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    • #3
      You may be lucky, like this chap, and find that you can reverse engineer the firmware to the point that you are able to update firmware or add new functionality.


      • #4
        Thanks, Peter yeah I figured. Any idea what language the original firmware may have been written in?

        PubBike, yeah I've looked at that! So cool. I can easily open the .rgn file for the 2006 (latest) firmware update for the FR201 (linked below), and can make basic visual changes to the text strings. It's just the hex file, so not much else I can do there, in terms of compiling new functionality to be added onto it. But will keep looking.

        While exploring that .rgn file I did notice that a list of datum are included even in the FR201 fw, even though it's not actually used in the unit at all (as far as I can tell). Wondering if it's just part of some stock code that got modified for the different-but-somewhat-similar units in that timeline. And/or if parts of the ForeTrex fw can be spliced in that would deal with the position formats under the 'Units' settings section.


        • #5
          Your next step might be to find out the chipset that the 201 uses. This might help you find a compatible disassembler that would help you start reverse engineering the code.

          The article here (in the appendix) suggests that the GPS chipsets were built by Garmin, so the whole thing might be custom which would means the disassembler will be harder to obtain, but you'll have fun finding out.


          • #6
            The rgn file is actually a container which contains other binary files. Without reverse engineering (which is illegal in most countries) there's just no way to do what you want.

            Best advice i can give is buy a new unit that supports connect iq so you can program against the exposed api (The foretrex you talk about is not connect iq compatible but if it has all the features you need you of course do not have the need to develop a custom app)
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            • #7
              It is for sure not illegal if it is just for private purposes, which this may be. If the OP was going to release it as part of a competing product then that would be illegal.


              • #8
                Originally posted by PubBike View Post
                It is for sure not illegal if it is just for private purposes, which this may be. If the OP was going to release it as part of a competing product then that would be illegal.
                Thanks, yeah, it was for my private non-commercial use. (unsure what specific bylaws govern Ontario, Canada)

                I emailed Garmin support a while back, politely explaining why I was looking for that info, they (reasonably) refused to share it. So I understand I probably won't be able to find this detail easily. Especially given how old this unit is, there's not much online either.

                For the time being I ended up getting an eTrex 30, so that suits my needs (and I actually like that it uses AA batteries, instead of something built-in). But will keep the old FR201 in case Garmin one day releases that legacy info and I can do some dev on that unit. Quite a few of those old foretrex and forerunner units are being sold on ebay/Kijiji and if chipset details become public they'd be a great tool for DIY projects.

                Thanks again for your help, guys.


                • #9
                  Full open source would be really great, but for DIY project would be HW specification and compiler enough. After that I would buy some old chart plotters and aviation computers just to have fun

                  I don't believe Garmin makes this true...


                  • #10
                    In case you'd like to venture further... The rgn tool will extract the binaries out of the packed rgn format, but realize that it's unlikely be able to fully decipher the enclosed bin files and when you start modifying the bin files and repack them in a rgn you'll of course have a considerable chance that you'll be bricking the unit....

                    choosing a new unit and picking up the monkey c language to deploy a connect iq program would be the better alternative.
                    Last edited by peterdedecker; 05-16-2018, 09:17 AM.
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