I see references in the comments to AF7 and the code isnsetting af_num to 7, which seems to match. This lines up with pins 19/20 being UART1.

Ohhhh, PA9 and PA10, not literally pins 9 and 10! I think it's starting to come together. Can you feel the excitement?

But why does the comment say USART2 init if it is really initializing UART1? Is it a comment that is wrong? A typo? Maybe they used to use UART2 and then switched to UART1 and just missed updating the comment?

The variable is named usart1, so it feels like a deceptive comment, but what does the code say? Will I be able to confirm it before it's time for the 2600 meeting? We'll see...