Finally got ATtiny3216 on PCB Working

This took so so long. Basically, I spent hours trying to get it to work. First, the 3.3V rail wasn’t getting power and the LED wasn’t lighting so I had to resolder the voltage regulator and then both green LEDs lit up, meaning everything was working.

Then I got my FTDI programmer, and plugged it into my PCB. Because I have a FTDI programmer and the ATtiny3216 has a UPDI programming interface, there is a resistor on the board to combine the two pins into one.

Even just getting megaTinyCore installed in Arduino IDE was a pain. The website that hosted the package info was down again, with an expired certificate. Apparently, this happens very often with it but I found an alternative mirror.

Then I tried flashing code, and it didn’t work. Then I realized that the board type I was using was the Optiboot version, and I couldn’t find the non Optiboot version so I had to flash Optiboot onto the MCU. I did not realize that doing this would cause problems later on. I also had to switch the programmer from the one that programs Arduinos to the UPDI programmer. But I STILL couldn’t get any GPIO to work.

I just tried things for hours. I switched to PlatformIO. I tried switching from C to Arduino in PlatformIO. I tried unplugging the programmer because I saw some voltage leaking from it. I tried emptying the caps and trying again. I probed every single pin to see if I wrote the wrong pin.

Then after all of that, when I switched to non Optiboot (having to find online that I have to downgrade megaTinyCore), and flashing that, it works. I think it was because flashing a bootloader burns some fuses to expect a bootloader, but when I flash my code it actually overwrites the bootloader code because I don’t have access to the TX and RX pins typically used to flash when Optiboot is installed, and that just caused the code to not run.