Wow, that's cool, thanks _very_ much for your help! :)
You gave me just the right shove in just the right direction - I was under the impression that the interfaces had changed and that that document was old.  (Adding to the confusion was that my old version of gpsbabel couldn't talk to the HCx either, until I upgraded to the newer version)... but anyway you were right, the document was right, and now it works!

The problem, if you're interested, was just a stupid one on my part - the garble code didn't take into account all of the specifications in that document (I did say it was much simpler than gpsbabel!) - and in particular didn't take any notice of the extended product data packets.  My old Vista never sends them so that's no problem but the HCx does, and that was screwing around with what garble was expecting to receive...  A second problem was that the Vista was sending waypoints as D108 (which garble understands) and the HCx sends them as D110 (which it didn't) - but now it's working for both tracks and waypoints, thanks for the help!
About the screenshot, I checked out that ximage program you mentioned (had to find a Windows machine first and for some reason install extra USB drivers?!) - but indeed that program can save bmp files from both units.  So it is kind of a supported function on both receivers, even if it isn't documented anywhere.  With the ext_product_data packets now understood, garble now gets as far as reading the dimensions of the image properly, but there's still lots of hacking around to do there with the data format.
First problem is to figure out the way the structure and sequence of the data, the second problem is that during getting the packets for the display data, it usually locks up the receiver (at random stages of the download) and gets a timeout - I guess maybe both sides are waiting for the other to respond.  Or something like that.
Anyway, just wanted to say thanks, and if I figure it out I'll send you what I found.

Robert Lipe <> wrote:
On Thu, May 8, 2008 at 10:36 AM, linux newbie <> wrote:

The only doc I found on was called the device interface sdk, unfortunately it was from 2006 and the only mention of Vista was a sidenote about version 2.12 of the software (my Vista is running

That seems about right.  They haven't introduced any *new* devices speaking Garmin protocol (the new ones are all file-based GPX models) in a long time.   The days of firmware version X and firmware version X+1 in the same model speaking different packet types for trackpoints seem to be behind us.

 Shame the pdf doesn't even _mention_ the screenshot function though :(

I said it wasn't documented. :-)

About the other gpsbabel formats, that's interesting, but not at all easy to find.  At least it confused me so much originally that I assumed gpsbabel couldn't do it.  It would be great if the list of formats included a one-line example, that way it would be much easier to spot which of the pagefuls of formats to experiment with.  I'll try the

I've considered that from time to time and  haven't ruled it out.  The reality, though, is that most users want "a file that works with [program]" and not "a file that contains the following fields".
About the screendumps yes I agree it doesn't fit too beautifully into gpsbabel, and I've no idea how much fun the integration would be, making it fit with the other functions.  And I have no clue how many models support such a

Most support it.  Garmin's 'ximage' page lists a couple dozen models.  We don't know how much variance there is in the protocols used across the line.   The fact that it's not documented means each  unit probably has to be tested and potentially reverse engineered individually, though my guess is that there is substantial "clumping" in the models, perhaps with variations for screen resolution and color depth, etc.


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