i've always tought if port are addresses:

when i do

in al,300h

i read the content of the conventional memory address 300h ?


I apologize for stupid question.

Bye A
Posted on 2001-10-15 15:53:16 by Bit7
not at all :). The way I have understood it, basically port access
go to the bus, where IO devices can intercept the data and do whatever
they need, and send back data. Port access can also be trapped
by drivers (ie, VXDs and KMDs) and do other processing, perhaps
afterwards sending it to the real IO device (this is done to virtualize
eg dos application that wants direct hardware access).

But port access definitely isn't the same as memory access :).

Btw, "better architectures" than the x86 usually means memory
mapped I/O. Here, writing to a special range of memory is used
for the port I/O, so the CPU doesn't have to have special instructions
for doing the accesses... pretty smart imo.
Posted on 2001-10-15 15:59:48 by f0dder
f0dder
THX,
now i'm beginning to understand...

bye
Posted on 2001-10-15 16:06:50 by Bit7
I like having the ports as addresses, and it's one of the first things I missed from the 68000 on the Atari/Amiga. On those systems you could do all kinds of cool stuff, by tweeking an I/O port - mainly video/sound hardware. :) Now there are no docs, and the drivers are there to hold our hand so we don't do no wrong. Someone thinks this is a more advanced design?
Posted on 2001-10-15 17:34:48 by bitRAKE
Interfacing through drivers is clearly good, since we are in a multitasking
environment, and drivers handle stuff like serialization of the devices.

However, the PC graphics/sound hardware was utter shit ?n the
beginning. This was a "serious" machine ;). The stuff modern gfx
cards can do are pretty neat, even if you have to use "highlevel"
APIs like DirectX (which aren't really all that highlevel, but sure, it's
more highlevel than blasting bits out on an I/O port ;)).
Posted on 2001-10-15 17:48:06 by f0dder
That's what took me so long to get a PC - EGA graphics are no where near what the Amiga 2000 could do! Yeah, I'd have to agree - a great deal has been gained by software abstractions - even if we do loose some control. I don't have to like it too much, though. ;)
Posted on 2001-10-16 17:23:39 by bitRAKE