this *looks* correct
```rs
        unsafe {
            // Borrow a mutable reference to the SpiDevice
            let mutex_spi = SPI_INSTANCE.get_mut();
            let spi_ref = mutex_spi.take().expect("SPI device not set");

            // Perform the SPI transfer
            spi_ref.write(buffer).expect("SPI transfer failed");
            
            // Return the SpiDevice
            mutex_spi.replace(Some(spi_ref));
        }