Message-Id: <m0zAxhc-000S4JC@inti.gov.ar>
Comments: Authenticated sender is <salvador AT natacha DOT inti DOT gov DOT ar>
From: "Salvador Eduardo Tropea (SET)" <salvador AT inti DOT gov DOT ar>
Organization: INTI
To: Poppleton <Alan DOT Poppleton AT wanadoo DOT fr>, djgpp AT delorie DOT com
Date: Mon, 24 Aug 1998 11:46:30 +0000
MIME-Version: 1.0
Content-type: text/plain; charset=US-ASCII
Content-transfer-encoding: 7BIT
Subject: Re: mapping i/o ports?
In-reply-to: <35DEAD9C.38821F62@Wanadoo.fr>
Precedence: bulk

Poppleton <Alan DOT Poppleton AT wanadoo DOT fr> wrote:

>     I just have a few questions about I/O ports.  I had heard somewhere
> that it is possible to map certain 

True, and that's *certain* not all.

> ports into memory, which speeds up
> the reading and writing of ports, is this correct?

Yes, most PCI video boards can do that.

>  If so, would it not
> be possible to map every port into memory, 

No.

> assuming there are 65536
> ports each longs 

They are bytes, not longs. When you address port 0x300 as a long you are 
writing in 0x300, 0x301, 0x302 and 0x303. Is like memory! just different 
signals used (I/O write instead of Memory write, etc).

> that would only take up 256K, which I certainly can
> spare if the speed up is significant.  Could anyone please tell me if
> this would be possible, and if so some example code on how it would be
> done.

You can't map all because:

1) Not all can be mapped, I think old chipsets can't do it at all and most of 
the I/O are used by the chipset (timer, interrupt controller, DMA controller, 
etc).
2) Different boards have your own I/O and your own mapping.
3) Normally when you map the I/O into memory the I/O dissapears so BIOS calls 
fails. In Trident boards if you map the I/O port in memory and you reset the 
computer it fails to reboot because the BIOS can't find the video board ;-) 
(you must turn off the computer).

The speed gain is marginal, the only advantage is that you can use the memory 
addressing mode to access I/O so the code is smaller and you use the 
registers better, but I/O still slow.

SET
------------------------------------ 0 --------------------------------
Visit my home page: http://set-soft.home.ml.org/
or
http://www.geocities.com/SiliconValley/Vista/6552/
Salvador Eduardo Tropea (SET). (Electronics Engineer)
Alternative e-mail: set-soft AT usa DOT net set AT computer DOT org
ICQ: 2951574
Address: Curapaligue 2124, Caseros, 3 de Febrero
Buenos Aires, (1678), ARGENTINA
TE: +(541) 759 0013