Interrupts on STM32 MCUs come in two flavors: internal and external. Both types of interrupts use the same core peripheral in the Cortex-M core: the Nested Vectored Interrupt Controller, or NVIC.

Using an STM32 and a custom PCB, he was off to the races in an incredibly cost-effective way. After writing some quick firmware in Rust, he was reporting the values read by the PWM channels.