Memory mapped IO - how is it done?

Question

I\'ve read about the difference between port mapped IO and memory mapped IO, but I can\'t figure out how memory mapped Io is implemented in modern operating systems (windows or

Answer 1

Are you asking about Memory mapped files, or memory mapped port-IO?

Memory mapped files are done by paging out the pages and intercepting page-faults to those addresses. This is all done by the OS by negotiation between the file-system manager and the page-fault handler.

Memory mapped port-IO is done at the CPU level by overloading address lines as port-IO lines which allow writes to memory to be translated onto the QPI bus lines as port-IO. This is all done by the processor interacting with the motherboard. The only other thing that the OS needs to do is to tell the MMU not to coalese reads and writes through the PAE must-writethrough and no-cache bits.