Function guarded_scan 

pub async fn guarded_scan<M: RawMutex, I: I2c>(
    bus: &Mutex<M, I>,
    reserved: &impl Reservations,
    lock_timeout: Duration,
    deadline: Duration,
    request: ScanRequest,
    out: &mut [u8],
) -> Result<usize, Status>

The scan counterpart of guarded_transfer: a range that covers a held address is refused whole rather than silently skipping it, so the host learns to try again instead of drawing a wrong inventory.