Hi,
        I thought something like that was happening.  The question now is, how do I
write the device driver, in what language, using what tools?

  Any info on that is appreciated.
  Many thanks to all who have replied.
 I've speeded up the plotting function using the SCANLINE command, even
though the image is compressed horizontally.  I'm still trying to figure
that out.

Again, Thanks

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Wojciech Zabolotny
Sent: Wednesday, December 27, 2000 2:55 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]: PIC data via PC parallel port to screen


On Wed, Dec 27, 2000 at 06:33:35PM +0000, Nigel Goodwin wrote:
>
> Any version of Delphi later than 1.0 (that is, any 32 bit version)
> doesn't allow you to access the hardware directly (version 1.0 had the
> Port() procedure) - so in order to do so you have to write a small piece
> of in-line assembler code - this is freely available on the net, and
> consists of a handful of op-codes. This then reads the port directly,
> and doesn't wait for Windows to give permission - which is why it's not
> included in 32 bit Delphi.
>
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.
--
                HTH
                Wojciech Zabolotny
                wzab@ise.pw.edu.pl

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