Just a quick update on OpenCore and the AMD cards. After lots of testing I finally worked out what was causing the driver error 43 in windows, it had nothing to do with signatures / checksums but was actually a problem with the display configuration, and fixing that got us TDM and native brightness control, no back-light mods required!
AMD Beta 4 roms are attached, they now all work with Windows installed in legacy MBR mode, but UEFI mode only works using a GOP vBIOS with the latest version of OpenCore. The higher wattage versions are faster but might not be stable on all systems. I included a 50W 560X version which might also work on WX 4130 /
4150 MXM-A cards, but probably only in the 2010 iMacs? (these cards are NOT detected in a 2011 27" iMac).
Remember there is more than one type of WX 4170 card, unfortunately I've now discovered that you can't just solder an EEPROM onto
either of
these cards, they are also missing a resistor network and other tiny components, so they won't work. But FlorisVN has found some of the
working type on
AliExpress which are ready for flashing.
AMD cards are complicated because in MacOS the frame-buffer "personality" is not just used to configure the display outputs but also tied to other things like brightness control / performance / power-management, which makes finding the right combination difficult. OpenCore & WhatEverGreen make life easier by giving us more control, as well as enabling features like HEVC (normally locked to specific models through SMBIOS / BoardID).
Although the Beta4 roms enable native brightness control, there is a catch:
[1] To enable brightness control and keep full performance in MacOS we use the generic "Radeon frame-buffer", but this seems to break High Sierra, causing a black screen during boot that is fixable using OpenCore / WEG or by connecting an external display. High Sierra users could just stick with Beta 3, which used the Salado framebuffer to restore performance but doesn't allow native brightness control. Beta 1 & 2 used the Longavi / Berbice frame-buffer which can work with native brightness control but also applied mobile power-gating that cripples performance in MacOS.
[2] Without help from OpenCore we can either have native brightness control OR the boot-screen, but not both. The back-light only turns on after a display driver has loaded, so to actually see the Apple boot-picker you would still need a back-light mod - which would obviously disconnect native brightness control. You could just use the boot-picker blindly, or wire a switch to the PWM line just to see it at boot time, but that is far from ideal...
However, thanks to great work by Startergo & Vit9696 we can now use OpenCore's GOP boot-picker instead, which also saves us having to do the boot-rom mod! These recent changes to OpenCore have delayed the release of the USB tool. Originally it was only intended to enable HEVC / SideCar for AMD and TDM & Native brightness control on some of the Nvidia cards, but now integrates several other fixes. Thanks to a lot of hard work by Highvoltage12v (and others) we are making good progress with it and should have something ready soon...
Edited, again, for clarity..?