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The Role of DSDT?


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#1
jacob_f

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Hello all,

I'm interested in where the DSDT sits, from what i've read so far it is stored in the BIOS, it provides a way a communicating with the hardware.

Here are my questions:-

* The DSDT is stored in the BIOS, but there are bootloaders out there that let you Mock/replace it. Does this mean that the DSDT is loaded along with the other ACPI tables directly into memory for the OS to access it? if so what normally does the loading into memory?

* What is the basic flow of messages to the DSDT. i.e. Kernel -> bootloader -> DSDT and back again? or is it different?

* Why is patching/recompiling of a DSDT on a regular PC necessary (to boot osx)? surely the DSDT living in the BIOS already knows how to communicate with the hardware, and i can't imagine that something in the BIOS would be specific to an OS i.e. windows, why can't OSX use a regular DSDT?

if anyone can point towards more information about the DSDT and BIOS that would be great,

Thanks.

#2
westwaerts

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DSDT is part of the ACPI Tables and resides in the BIOS.

It tells during boot which hardware is to find on your Computer
and loads the respecting kexts (drivers) for it.

Though OSX is normally not loaded from a BIOS file, but from an EFI Hardware,
there are differences in the boot process. Also Apple has fewer hardware components, than in the PC world,
so without help ( injection, deviceID tricking) the hardware remains unrecognized for OSX.

So some bootloaders are capable of loading a different DSDT ( than the one implemented in the BIOS)
and match better to the OSX Hardware.

Get yourself IOReg Explorer and read along the threads here and you get wisedom.





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