See here:
Hello all, [Update Jan 2021 - This driver has evolved to the Lume X1, check it out here! https://budgetlightforum.com/t/-/65319 ] It's been a long while (half a year or so?) since I've been back to BLF, and I hope everyone is having a good start to 2018! Over the past some two weeks and a half a lot of things has happened so I'd thought I'd share some here. It all started from when I found some time to do a proper write-up for my GXB17 driver which you can read in detail on my webpage here. …
and here:
GitHub - loneoceans/gxb172-attiny841: Firmware for GXB172 Flashlight Driver; Atmel...
Firmware for GXB172 Flashlight Driver; Atmel ATtiny841
Hope this helps.