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From: Andi Kleen <ak@muc.de>
Subject: Re: question re Ada equivalent of C function
Date: 1998/02/22
Message-ID: <m3vhu7twno.fsf@fred.muc.de>#1/1
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Organization: [posted via] Leibniz-Rechenzentrum, Muenchen (Germany)
Newsgroups: comp.lang.ada
Date: 1998-02-22T00:00:00+00:00
List-Id: <comp.lang.ada>


dewar@merv.cs.nyu.edu (Robert Dewar) writes:
> 
> I am not suggesting that everyone move to OS/2, just pointing out that
> the chain of reasoning that X is a "real operating system", therefore
> X cannot allow you to directly access an IO port is misleading.

Linux allows this too, although only if you have root rights. Just
call the iopl() system call then to gain access to the io ports you
need.  

Often it is better design to write a small kernel level driver 
stub though to access the hardware and control it over a device from the
user program. For example it is pretty bad to disable interrupts in
user programs (it is possible with some ugly tricks, but will probably
break on SMP machines) - and often accesses to io ports require that for
race-free operation. Overall doing io port accesses in a kernel level 
driver is better in most cases.

-Andi