Function recv_timeout 

pub fn recv_timeout(
    endpoint: CapHandle,
    timeout_cycles: u64,
) -> Result<Option<Message>, IpcError>

Blocking recv with a timeout in counter ticks (the kernel waits at least one scheduler tick): Ok(Some(msg)) on a message, Ok(None) on timeout, Err on a real error. timeout_cycles == 0 blocks forever (like recv). (syscall 35 - recv_timeout) Lets a driver idle on its interrupt yet still wake on a timer (e.g. for keyboard auto-repeat while a key is held - §12).