Problem Statement

In systems programing it is sometimes required to place language objects at specific memory locations, like I/O registers, hardware interrupt vectors etc.

Show how language objects can be allocated at a specific machine addresses. Since most OSes prohibit access to the physical memory if it is not mapped by the application, as an example, rather than a physical address, take the address of some existing object (using suitable address operations if necessary).

For example:

Let's start with the solution:

: (setq IntSpace 12345)          # Integer
-> 12345

: (setq Address (adr 'IntSpace)) # Encoded machine address
-> -2969166782547

: (set (adr Address) 65535)      # Set this address to a new value
-> 65535

: IntSpace                       # Show the new value
-> 65535