operating system - The CPU, BIOS, or OS does the IO port address assignment? -


i understand cpu communicates io devices through io port address (usually 16-bits) i'm wondering io port address assignment? bios? cpu? os? these addresses preset or dynamic?

normally addresses of addressable i/o assigned hardware.

literally, there logic circuitry (either internal processor or external) watches bus specific address, , causes peripheral function register latch data being written off bus, or drive data being read onto it.

sometimes address of particular peripheral sum of base address , internal address, base address may determined dip switch or jumpers or (in historic cases, not in ibm pc) slot expansion card plugged into.

in more complicated interfaces such pci, possible i/o base address might(?) assigned software after discovery. while traditional local bus interface can few logic gates, pci interface quite complicated lot of configuration capabilities.


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