Introduction
Use bootloader to dump flash data. Actually it is an exploit for built-in bootloader.
Verified in CH558 with bootloader V231. CH559 should be okay too. Other chips (CH551/2/4) could be referred, but I'm not sure.
Thanks for MarsTechHAN/ch552tool to provide this idea.
Usage
Please install Python 3.x and PyUSB first.
pip install pyusb
Then, plug your device and make sure it in download mode.
For Windows, use Zadig to substitude the driver of "USB Module".
Finally, run dump.py and wait until it is done. It would take much time, so please be patient.