Function try_wait_vblank 

pub fn try_wait_vblank(spins: u32) -> bool

wait_vblank with its own bound: true once the count has advanced, false after spins reads of it without a change. A false means no VBlank interrupt reached psx-rt’s handler: interrupts are masked (inside a critical_section), the counter was never installed, or a game’s handler does not chain to psx-rt’s. Does not install the counter; wait_vblank does that first.