The CDC $6000$ series computers $($originally designed by Seymour Cray$)$ had a set of peripheral processing units $($PPUs$)$ that were independent of the main CPU$($s$).($Some models had a single main CPU and some had two.$)$ The PPU had an instruction called the exchange jump $($EXN$).$ There was a PPU register called A which specified the address of a block of memory. When the PPU executed the EXN instruction, the main CPU was interrupted, all of its registers were exchanged with the block of memory pointed to by the PPU A register, and the main CPU resumed operation. If the operating system is running on a PPU, describe how to perform a context switch using the EXN instruction. $($Note: This question is not asking you to implement the EXN instruction. It is asking you to use the EXN instruction to implement a context switch.$)$