How is the UnsafeCell used?

```
let buffer: &'static mut [u8] = /* ConstStaticCell stuff */;

buffer[0] = 1;
buffer[1] = 2;
buffer[2] = 3;

dma_reg.ptr.write_volatile(buffer.as_ptr());
dma_reg.size.write_volatile(buffer.len());

compile_fence(Ordering::Release);

dma_reg.start.write_volatile(1);
```

Insert it into the pseudo code above plzzz