Sounds very useful to anyone using a PC that predates PS/2 or USB. I use an optical PS/2 mouse with a KVM though, so not much use for me. Well done for starting this project though, amd especially for making it open source.

Thanks for the feedback!
If you use a PS/2 mouse, you might be interested in checking out my related project.
It’s a replica of an ISA adapter for a PS/2 mouse, which the system recognizes as a UART-based serial mouse:
https://github.com/Yftul/ps-2-mouse-to-isa-replica

the usb controller in this card offloads the work from the cpu? because even on a k6-2 the usb is a resource hog when in use

Yes, this controller is completely equivalent to a serial mouse and does not burden the processor with the complexities of USB implementation.

Card looks nice. Slightly off topic, but it looks a little strange when the isa contact pads are perfectly rectangular. They always used to have a semi circular top back in the day. Was there a reason for that?

Yes, it’s using the standard ISA connector footprint from KiCad.

This is great! I had an idea in my mind something like this a while ago, but I don't know anything about FPGA/CPLD... 🙁

But isn't that Altera CPLD an obsolete part? You can't buy it new anywhere - only found on eBay, AliExpress, etc. Such sources are... questionable, with good chance of being ripped off with fakes and bad parts.

It is mentioned here that ATF1504AS might be usable, but I haven’t verified it.

Yeah, the Atmel parts are usable. There even is a progarm to convert the Altera POF into Atmel format to burn on the Atmel parts.