29 Oct
2010
29 Oct
'10
6:29 a.m.
On Thu, Oct 28, 2010 at 2:24 PM, Johnny Billquist <bqt at softjar.se> wrote:
But, as some pointed out, the x86 do not use
memory mapped I/O (and shared memory with a graphics subsystem is not the
same thing). Most RISC machines did/do use memory mapped I/O anyway, but I
digress...
Sure modern x86 systems still have port I/O instructions and some
devices that are accessed via port I/O instructions, but a lot of
modern PCI/PCIe attached devices are accessed only via memory mapped
I/O registers. For example the original Intel UHCI USB host
controller design was accessed via port I/O instructions but all
subsequent USB host controllers designs (OHCI, EHCI, XHCI) are access
only via memory mapped I/O registers.