So I currently have the BLE GATT downloading working on both my Suunto EON Steel and the Scubapro G2. This is to see if anybody else wants to play with the code, but before looking at the code, a few faily big caveats:
(a) BLE is not fast. Just be warned. You *will* be happier with a USB cable if you have that option.
(b) divecomputers are odd, and not a lot of people seem to play with them over bluetooth. At least Suunto seems to consider the BLE to be mobile-only. On desktop systems, bluetooth seems to be pretty hit and miss outside of legacy mouse/keyboard/audio things. Odd BLE devices? Yeah, bugs will happen.
(c) I only work with Linux, and I don't do mobile. End result: right now the code only works on Linux laptops and desktops with bluetooth. A regular BT-4.0 USB dongle works fine for me on my desktop, and my laptop has Intel wireless with BT that also works. So as long as it's LE-capable (and not all BT dongles are), it probably works.
(d) ...but I found several "features" due to (b), and you'll not only need a fairly up-to-date Qt installation, you may need to literally build your own due to Qt bugs (the EON Steel in particular is very picky, and Qt/Bluez didn't connect to it without patches).
(e) my BLE code is not pretty. It's scary. In fact, it can probably be used to make small timid pets pee on the floor in fright. You have been warned.
With those encouraging words, here's the scoop:
If using Qt, use at least 5.9.1, and if you want to play with the EON Steel, make it work on some non-Bluez platform (which has so far never been tested - Bluez is what the Linux desktop environments use), and use the patch from here:
https://codereview.qt-project.org/#/c/198202/
You also need to make sure that you have "device privacy" enabled, at least in order to pair with the EON Steel. It will not talk to you unless you have a device identity key ("IRK"). With Bluez (ie Linux desktop environment), this involves making sure that you have
Privacy = device
in your bluetooth config file (normally /etc/bluetooth/main.conf, and normally it it set to "off").
Also, make sure that you have the current libdivecomputer Subsurface-branch, which has the code for the EON Steel and the Scubapro G2 to know the differences between a USB HID download and a BLE GATT download.
And if y ou do all that, and if you apply the attached patch to the current subsurface source base, and if you walk around three times widdershins around your computer while you build it all, you *may* just get working BLE GATT downloads.
I'll hopefully look at the Shearwater Perdix AI next. Since BLE is the *only* way to download from that dive computer, it would be really nice if I can make this work for that too. We'll see.
Linus