70Hz vsync fix for Hand386

The Hand386 handheld PC released in 2023 is a really cool gadget and has taken the retro PC world by storm. The Hand386 comes with a Chips & Technologies 65535 VGA controller, and unfortunately the video BIOS that comes with the Hand386 sets it to flat panel output mode, forcing all video to 60Hz vertical refresh. The device uses a Realtek flat panel controller that takes a VGA signal, and it has no problem syncing to the 70Hz VGA mode.

Programs that expect the standard VGA modes to be at 70Hz may run too slowly or have other strange behavior when forced to 60Hz. For example, music in the demo Second Reality by Future Crew has a tempo that is slower than normal.

Running it

Download handfix.com from the Releases section of this repository and copy to your Hand386. Run handfix.com to re-enable 70Hz VGA modes (and other tweaked refresh modes). The first time you run it, it will take some time to auto-adjust the screen. Enabling 70Hz modes is not permanent – to bring back the old 60Hz force behavior, power down and restart your Hand386.

Screenshot:

<img width="719" alt="handfix" src="https://github.com/polpo/hand386fix/assets/1544908/4c7c32ff-7e50-47c4-a378-6062a3103e11">

Caveats!

The auto-adjust that the screen undergoes may not be perfect. On my Hand386, the bottom is cut off by a few rows of pixels. Currently there is no way to re-trigger an auto-adjust on the Hand386. This utility fills the screen with a blue background in an attempt to get better auto-adjustment.

Before and after

See (actually hear) the difference in this video:

<img src="https://img.youtube.com/vi/o0BhFbuwMuM/maxresdefault.jpg" alt="YouTube thumbnail" width=600>

Credits

References: Chips & Technology 65535 datasheet, available at: https://www.yyzkevin.com/pc110/65535-2/

Thanks to yyzkevin for his knowledge about the C&T 65535!