ATTINY88 High Voltage Parallel Programmer

This project came from a bricked attiny88. I was changing the fuses, and after one particular update, none of the methods to program or update fuses worked. The programmer was unable even to read the signature or fuses. However, the code was still working, albeit terribly slowly. An LED which previously blinked once per second was taking minutes to complete a blink cycle. While ATTINY88 microcontrollers are inexpensive and could easily be replaced, I took it as a challenge to unbrick this one. Reading the datasheet and online, a high voltage parallel programmer was what was needed, but I couldn't find code or a schematic, so I worked to get a hvpp programmer working.

This was validated working with a purple pi (off-brand rp2040), a 12v boost regulator, and the aforementioned bricked ATTINY88. I was then able to use the WRITEFUS command to unbrick the device. I implemented a few additional commands as well. The entire suite of possible commands is not yet available, but should be doable leveraging the primitives that are already implemented.

https://github.com/rhhayward/attiny88-hvpp for description and code