> In message <20001227205505.A1199@wzab.nasz.dom>, Wojciech Zabolotny
> <wzab@ISE.PW.EDU.PL> writes
> >No way !!! The IO-permission mechanism in Windows uses the CPU hardware,
so
> >it does not depend on the language (ASM vs Pascal). When the user (not
"ring
> >0") program executes the "in" or "out" operation, an exception occures,
the
> >kernel check wether this port is "virtualized" and either performs the
> >standard in/out or executes the dedicated procedure provided by the
> >appropriate VxD driver...
> >The only way to avoid this time consuming overhead is to write the device
> >driver, which is a piece of code which executes in the "ring 0" (like the
> >kernel).
> >This is true not only for Windows but for all "true" operating systems
like
> >Uni*es (including Linux). However in Linux one may write the standard
> >program executing with root privileges, which can perform direct I/O
without
> >loss of performance.

> You're talking about Windows NT, it works fine under 95, 98, and ME,
> considering NT is very much a minority operating system only a small
> percentage of user would have a problem with this. My 32 bit PIC
> programmer uses a driver DLL so it works with NT, otherwise I would use
> direct access just like the 16 bit version.

NOT TRUE! Win95/Win98/WinMe _DO_ trap port I/O for virtualization. It is
just that for many cases (ie: parallel port) they simulate the I/O and allow
it to complete. This is _SLOW_.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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