Question on MMAPIO ...

[Reinhold J. Gerharz]

At 03:41 09/02/1998 +0200, Patrick Mau wrote:
>On Mon, Aug 31, 1998 at 05:10:57AM +0200, Patrick Mau wrote:
>> 
>> Dear Adaptec Users,
>> 
>> I have a question regarding memory-mapped I/O with linux.
>> I'm using a pretty old AHA3940 PCI Dual Channel PCI controller and
>> ever since MMAPIO is defined in this driver I have to undefine it.

I don't know the context to which this term is applied in the driver
(no source code in front of me...), but traditionally, memory mapped
I/O describes an architectural feature. A part of the memory address
space is reserved for I/O control and data registers, as found on the
once ubiquitous PDP-11. To access these, the same machine instructions
are used as those that operate on main memory. The X86 architecture,
on the other hand, distinguishes between I/O and memory by using
special instructions just for doing I/O, thus leaving the entire
memory addressing range for just that; memory.
-- 
Reinhold J. Gerharz                        http://www.gerharz.net
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