A record of reverse engineering by noob
Special thanks to kagaimiq

Discovery of tools and informations
Beginning of reverse engineering
Reverse Engineering Part 1
Reverse Engineering Part 2
Reverse Engineering Part 3 (Jump Here For Latest Information)
Reverse Engineering Part 4

Recently, I found these rather interesting tools and forum about JieLi.

jl-uboot-tool
jl-misctools
USMI Forum

Although I don't have any knowledge about python, but I immediately downloaded tools and installed IDE, and other requirements anyway.
So I ran the UBoot tool and tried to dump firmware from a few devices with JieLi chip, but for some reason, it doesn't work well. But I tried dumping from AC6921A development board with JL Downloader dongle, it worked well. On the other hands, I also tried the firmware unpacker and it successfully unpacked. So I started googling "jl_690x.bfu", downloading BFU file, removing BFU header and pushing into unpacker. Most of firmwares I downloaded could unpacked successfully, but some of them seem to have different structure.

A few days later, I was having a look at USMI forum, then I found another tool called JLDFUTool. I downloaded it and tried to dump from my Chinese Bluetooth Speaker called WS-2015, and yes! It could dump firmware, but there were some CRC mismatch too.

(I don't care such lil thing, I wanna unpack it now!)

I have a toolchain for AC46, which has DV10 compiler, so firstly I pushed dump into fwunpack_dv.py, but it said SYD header CRC mismatch. So I tried 690x one, and even the new firmware one, but nothing worked well except for old generation stuff, called sydtools. I didn't know what is the SYD, but I was about to understand what it is, and why the dedicated unpacker doesn't work.

(Continue to Reverse Engineering Part 1)