All I/O operations are memory-mapped. There are no port-based I/O instructions.
Memory-mapped ports often have different properties than normal RAM:
* A read-only port is what it sounds like. Attempting to write to this address will not affect the contents.
* A write-only port can be written to, but reading it will result in undefined behavior. The value read from the address is not necessarily what was last stored in it.
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