Accessing Hardware Protected Mode

This is a discussion on Accessing Hardware Protected Mode within the Tech Board forums, part of the Community Boards category; Didn't know where to post this so I through it up in here. What is the best strategy for accessing ...

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    Registered User valaris's Avatar
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    Accessing Hardware Protected Mode

    Didn't know where to post this so I through it up in here. What is the best strategy for accessing hardware addresses on your computer, or is it indeed OS specific? For instance, if I wanted to access some registers on my video card, or get access to a GPIO port how could I go about doing it in a protected mode setting? Or is it impossible/reliant on the OS to supply system calls for this? If this is the case what API would I utilize to access hardware under XP/Vista?

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    Kernel hacker
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    Protected mode in x86 allows the OS (kernel mode, ring0) code to prevent any and all access to memory and IO ports. In fact Windows does exactly this (as does Windows).

    There are some drivers available that can poke holes in the security system - particularly allowing code in user-mode to access IO ports.
    For example this:
    http://www.beyondlogic.org/porttalk/porttalk.htm

    However, for most intents and purposes beyond simple applications to modify the status of the parallel port pins, you probably need a kernel driver to access the real hardware. Writing drivers is a fairly sophisticated way of dealing with hardware, but unfortunately, it's the way that the OS wants us to work with things.

    To write Windows drivers, you need a Windows Device Driver Kit for the OS you are targetting (although the latest kit also has support for older OS's, so the Vista WDK will be fine for XP or Win2K - Win9X has a completely different driver architecture, so I'd ignore that alltogether). You probably also need a second PC, so that you can use WinDbg to debug the driver - also, you probably don't want to mess up your current PC by for example using a block of memory after freeing it [and the filesystem decided that's where it's going to put some important file-data that when it's written over by your code prevents the file-system from ever working again!]...

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    Jack of many languages Dino's Avatar
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    Quote Originally Posted by matsp View Post
    ... also, you probably don't want to mess up your current PC by for example using a block of memory after freeing it [and the filesystem decided that's where it's going to put some important file-data that when it's written over by your code prevents the file-system from ever working again!]...

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    Been, there, done that, have we?
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    12/20: Mario F.:I never was, am not, and never will be, one to shut up in the face of something I think is fundamentally wrong.

    Amen brother!

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    Quote Originally Posted by Dino View Post
    Been, there, done that, have we?
    Not quite I never thrashed the hard-disk, but I managed to mess up some internal data structures in the OS so it crashed - weird blue-screens that you don't expect, in modules that you didn't even know existed.

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    Compilers can produce warnings - make the compiler programmers happy: Use them!
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    C++まいる!Cをこわせ! Elysia's Avatar
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    So why do you need to directly access hardware?
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by Elysia View Post
    So why do you need to directly access hardware?
    Why not aspire to learn something? You don't have to stay in application land all the time.

    Depending on what kind of access you need, you can do a lot from user mode on Windows. You could use NtOpenSection() on "\device\physicalmemory" followed by NtMapViewOfSection() to bring portions of physical addresses into your address space.

    And I'm sure there is a way to read and write ports, if you have proper privileges. All of it probably requires administrator privileges.

    Have fun locking up your computer
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

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    C++まいる!Cをこわせ! Elysia's Avatar
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    Sure.
    But sometimes it's also a bad idea to directly access hardware.
    Depends on the why.
    So if it's for learning, I say go right ahead, but if it's some hackish solution to a problem, then I would say step back a bit and think it over.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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    Registered User valaris's Avatar
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    Quote Originally Posted by Elysia View Post
    Sure.
    But sometimes it's also a bad idea to directly access hardware.
    Depends on the why.
    So if it's for learning, I say go right ahead, but if it's some hackish solution to a problem, then I would say step back a bit and think it over.
    100% for fun. I have been playing around with various flavors of microcontrollers, and wanted to play around with my pc at a lower level as well. Mostly to learn how things are happening at a lower level.

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    C++まいる!Cをこわせ! Elysia's Avatar
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    Good luck then, and have fun!
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  10. #10
    Malum in se abachler's Avatar
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    Quote Originally Posted by valaris View Post
    100% for fun. I have been playing around with various flavors of microcontrollers, and wanted to play around with my pc at a lower level as well. Mostly to learn how things are happening at a lower level.
    Try http://forum.osdev.org/ its a fairly decent site for learning low level stuff.

    You can find that and other sites deedicated to OS development at - http://www.google.com/Top/Computers/...ating_Systems/
    Until you can build a working general purpose reprogrammable computer out of basic components from radio shack, you are not fit to call yourself a programmer in my presence. This is cwhizard, signing off.

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