Update: I think I may have found the problem for those of you that can't enable a second monitor using HD530.
Since the recent release of 10.11.5, when I updated I lost the ability to hot plug my second monitor at the desktop. The only difference on my system is, before I was using the Nvidia GTX970 and to use this with an iMac17,1 system definition I had to disable Apple's Graphics Device policy. This was disabled when testing HD530/dual monitor in 10.11.4 and was unaware it affected HD530.
Using HD530 with an iMac17,1 limits you to one boot display and no second monitor unless you remove Apple Graphics Device policy. HD530 is restricted too as is the Nvidia cards with this system definition. Now I've disabled Apples graphics display policy in 10.11.5 hot plugging my second monitor is working.
If anyone wants to test/confirm my theory go ahead and apply the fix in Problem 4/Method 2 here :
Solving NVIDIA Driver Install & Loading Problems Restart required.
Alternatively use shilohh's app at the bottom of Post#1 here:
Black Screen with MacPro 6,1 or iMac 15 or iMac 17 System Definition Restart required.
Any chance you could help me a little with this, wildwillow?
I have a clover installed on a GA-Z170N-WIFI with an i7 Skylake CPU, and internal integrated Intel 530 graphics, connected to a monitor over HDMI running 10.11.5 (El Capitan). It works fine, but I am trying to add a second monitor over HDMI and encountering issues. My system is configured as an iMac 17,1 and I am loathe to change it and break iMessage.
The first problem I encountered was that very early on in the boot process (I think at the time Clover is run, or possibly before) the second monitor would display 'snow' and random noise would appear over HDMI. I rectified this by changing the DVMT pre-allocated memory in BIOS from 64MB to 256MB.
Now both monitors on boot display the BIOS screen, both display the same Clover screen, both display the apple logo, but the second one switches off about 3/4 of the way through loading. Shortly after, the main screen is corrupted. Using screensharing, I can log on fine.
It sounds like I need to 'disable Apples graphics display policy'. However, I am confused by the links given. The first link seems to be to an NVIDIA thread (I don't have NVIDIA but maybe there is commonality). I'm not sure of the relevance of the precise item linked to, but on the first page problem 4 method 2 simply contains a link to the second thread. The second thread, which I've read through, is a bit confusing. The first page refers to NVIDIA and Yosemite; presumably a patch for Yosemite is going to work on El Capitan. Secondly, it suggests
"For those of you using MacPro6,1 and willing to get a little more geeky, assigning the name GFX1 to your GPU in your ACPI tables (DSDT or SSDT) will also work without the need to patch any kexts and you won't need to worry about re-patching anything after OS X updates unless Apple changes the device policy again". That seems like a good option (and seems to be what other people are doing in this thread, though I don't know what else). Any chance someone could explain (simply) how to do this?
I suspect the answer may be within this paragraph:
If you currently have GPU injection via DSDT or SSDT, it's as easy as changing the name. Open your DSDT or SSDT in your editor of choice (I prefer MaciASL) and change GFX0, PXSx, PEGx, or whatever it's name currently is to GFX1. Click compile and save it. If you don't currently have have your GPU injected in your DSDT or a SSDT,
see this Guide to create one or more SSDTs for your GPU/s.
However, I don't know whether I have 'GPU injection via DSDT or SSDT'. I simply ran Clover and followed the guide
here (ignoring the NVIDIA bits obviously). What (exactly) do I need to do? Apologies for a newbie question; I'm sure the answer is obvious to most of you.
