Quick update. OpenCore 0.6.8, Big Sur 11.5. System definition iMac15,1.
One thing to fix: Bluetooth sound input (IOGear 4.0 adapter) was broken until I added kexts from BrcmPatchRAM 2.6.0:
What version of the bios are you using? I ask because in my system (same motherboard), using the latest bios was the only thing that solved random memory corruption on long sleeps. This was way back in Sierra.
For those of you with an old machine like this. Big Sur runs fine, native graphics drivers. Switched to OpenCore, which was an interesting adventure. Worked the first time, thanks to the excellent guides online. Config included for reference (minus MLB and other identifiables)...
Decided to get back to this. Switched to OpenCore and all new kext. Fresh install. Worked perfectly.
Changed machine type to iMac15,1 and then upgraded to Big Sur. Everything works, except video playback in iTunes.
Updated WEG, Lilu, AppleALC, no luck upgrading from Mojave. Graphics hangs (black screen). Tried a few things without luck (disable IGPU, agdpmod=pikera, remove GPU card). This is an old machine, so maybe I need to go through and clean up old kext.
I have searched the system logs and cannot even find any associated error message or report. It looks like the graphics engine just hangs.
Also, video in Chrome did not crash, but there were noticeable glitches (slight pauses and jumps), something I have never seen before on this computer.
USB 3 is now working. This post from matt77303 was very helpful. I just followed the instructions.
Well, it looked like it was working according to System Report (here I have a USB 3 drive installed). I tried to run some adhoc benchmarks (using the mkfile and iostat commands), but I don't have...
Getting sound working after sleep took a lot of experimenting, despite some of the very helpful references in this site.
It does appear that the problem is associated with power modes on the Realtek chip, because CodecCommander (version 2.4.0) was ultimately part of the solution. Note that all...
I am not sure this is conclusive or not.
Well, the machine would eventually complete its boot if you kept on trying, without altering any settings. Once booted the machine would run fine. So I figure this is some subtle timing issue in the driver on startup, which I guess would be real easy...