Those framebuffers usually match AMDs reference layouts (see below), so they wont help you in case of any odd custom design card.This would make many people assume that they werent compatible with OS X at all, but in fact Apple has included driver support for almost every relevant AMD graphics chipset from the last years, so theres a good chance your standard PC card will work out of the box However, before getting too excited there are a few things to consider to achieve hassle-free long-term compatibility, so Ive composed this guide to collect all necessary information and to clarify some urban myths.
Ati Radeon 4870 Flashed How To Find PerfectlyIll explain how to find perfectly compatible cards and how to improve the overall experience on not so compatible GPUs.This wont be a super-detailed step-by-step tutorial on every single aspect, but instead an overview on most important topics with links to further information.
General Information To choose a compatible graphics card it is helpful to know some details about the operation principles of the AMD drivers. Ati Radeon 4870 Flashed Code Of ThoseObviously I have never seen the source code of those drivers so my knowledge isnt as deep as it could be, but for the scope of this guide itll be fine. The first is responsible of setting up basic 2D operation, correct resolutions, handling the connection ports of your card (rooting the signals to the correct ports, detecting hot plug actions, handling multiple screens) and others while the latter is mainly responsible for the 3D acceleration of your card. Both types of kexts contain a list of PCI device IDs in their Info.plist to detect and properly initialize connected GPUs. Having the device ID of a specific card in both files is necessary but not sufficient to make it work Apple will add some device IDs every now and then, and while some of the added cards will actually work, others might have awfully buggy drivers because Apple added the IDs just for testing purpose. Do not buy a card assuming its fully compatible just because you see the device ID in there There are some cards which are very similar to supported cards but still dont have their device ID in the drivers. Ati Radeon 4870 Flashed Update And YoullThey can usually be enabled by either modifying the Info.plist of both kernel extensions (not recommended, because changes will be lost on the next OS X update and youll violate the kext signing) or by spoofing your GPUs device ID with Clover. Initialization Process If the PCIe device ID of the installed card has a match in Info.plist files, it can be initialized. There are two ways to make that happen, Ill call them EFI-Init and Auto-Init. On startup, this EFI binary will be executed by the machines EFI, which will introduce the card to the system thus initializing the driver. On a Hack, this can be mimicked by the bootloaders Graphics Injection functionality. This way you can tell the system which Framebuffer to use (see next section) or how the card shall be called in the System Profiler. Some of you will also remember tools like ATYInit.kext which can basically do the same. Apple gave the system the ability to initialize a PCI graphics card just by its legacy vBIOS, without the need for any (faked) EFI stuff. At the beginning this had some compatibility issues, but as of Yosemite one can say that in most cases this works as good as the classic EFI-based injection method. You dont have to do any setup for this to happen, but please remember that the drivers being loaded might still be crap and only give you a garbled or black screen. Framebuffers Each of the AMDx000Controller.kexts contain a set of so-called framebuffers for one GPU family. For the scope of this guide you can think of them as set of port mapping tables, which tell the driver how each port of the graphics card is physically linked to the GPU chip. This is important, because a mismatch might result in a black screen, system freezes or a lack of certain features (e.g. Most of those framebuffers are Apple specific (e.g. LVDS port and 2 DisplayPorts for a MacBook), but in the past they were kind enough to include some framebuffers for generic PC video cards despite they didnt use any themselves.
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