sun.misc.Unsafe isn't part of the Java standard. Thus, your very first task will be determining whether the Java implementation you will be running on the ARM chip supports it.

If the answer to the above is yes, you have to ask yourself whether the I/O addresses you need to access are mapped within the JVM *process*. Unsafe lets you escape the usual Java memory model, but it doesn't have any facility to escape the JVM process's address space. It would not be unusual for hardware I/O addresses to only be writable from kernel address space, but your platform may be different.

Assuming you have the I/O addresses mapped in the JVM process, then the last hurdle is checking whether all the protocols you plan to use are slow enough or flexible enough with time that you can drive them from a Java process, which may be subject to stop-the-world garbage collection and other factors that make it not-even-remotely-real-time.

If all that checks out, it sounds like an interesting project.

Oh wait, you also have to figure out a way to fit Linux and a JVM in 512KB of flash memory ... and run them in 100KB of RAM. It sounds like you would need to upgrade to a significantly more powerful chip to carry out this concept.