Solved Strange behaviour of Windows 11 when trying to access UEFI with CSM disabled

Version 22H2 (22621.963) Gigabyte AORUS Master X570. AMD Ryzen 7-3700X. All my hard disks and SSD's are GPT.
A few weeks ago I discovered that it is possible to enter UEFI from within Windows 11 ( Settings>System>Recovery>advanced Startup>Restart Now) OR <Shift>Restart
Both these methods lead to a blue screen at which there are four menu options. 1) Continue to to Windows11 2) Use a device to boot 3) Troubleshoot 4) Shut Down.
UEFI is entered by selecting Troubleshoot and then UEFI Firmware Settings.
Until discovering these methods, I had always hit F12 or Del at Post to enter UEFI.
In the two years or so since I built this PC, I have been using some UEFI settings as follows:
SVM Mode (virtualisation) ON
XMP Profile 1 (Memory overclock provided by Corsair) for PC4-3200R
fTPM ON
CSM Support enabled (default)
I have never set Secure Boot, and I believe that Windows 11 demands the ABILTY to secure boot, but does not enforce its switching on. It is set to auto, which means it uses the previous setting. MSINFO32 show it as NOT SET.
Last week I upgraded the UEFI to F36, having used F35 for twelve months.
Since I only have Windows 11 on my PC and have no need of an ability to boot into a BIOS based OS. I decided to disable CSM.
A few days later, I needed to check something in the UEFI, so I tried to get into it from Windows 11. Everything went well until I hit "Troubleshoot" followed by "UEFI Firmware Settings"
At that point my PC froze, with a black screen.
I waited for 5 minutes and then I repeated the process (by first pressing power to shut down), but the same thing happened.
I reverted to F35 UEFI with the same settings - same problem.
My motherboard has an LED display showing how far it has got in the POST, and it had stuck at a6 (which means "Detect and install all currently connected SCSI devices"
Naturally, I then went into Windows to check all my disks (SSD and HDD), and they are all GPT.
I discovered that I could still get into UEFI at POST by hitting Del or F12
Switching CSM back to "enabled" fixes the problem.
Has anyone any idea why this should be?
It may be a Gigabyte issue, but the fact that I can still get into UEFI by the old-fashioned method, and it is only when trying to get in via Windows that the problem occurs, makes me think that it is a Windows issue.

Rep

@jameswesthead

I just left CSM enabled in my BIOS. (Asus Pro WS X570-ACE motherboard)

your reference to "UEFI" is actually called the 'BIOS"
(Basic Input Output System)

Thanks Ghot, I have been doing just that. However, I would like to use Secure Boot, an that means I must disable CSM. Of course, I can always get into UEFI at POST time (but maybe not if I enable Fast Boot or certainly not if I enable Super Fast Boot).
Thanks KYHI. UEFI is the successor to BIOS, and my motherboard uses UEFI unless it s necessary for it to use BIOS for some OS other than Windows 11 - hence the CSM. setting I don't want it to use BIOS because I would like to enable Secure Boot, and it insists on UEFI only (i.e.CSM disabled)

CSM stands for compatibility support module.
It is an optional tool included in the UEFI firmware that allows legacy BIOS compatibility for older OS.
What does it say for bios mode in msinfo?
Start>run>msinfo32
If it says UEFI you are using UEFI.
If it says Legacy you are using the CSM module.
Try going into bios with Del or F12.
Next steps work better if you change them one at a time saving in between changing them.
Go to BOOT, disable 'CSM Support', 'Save and exit' and come back to the same BOOT menu. Now, go to 'Secure boot' and enable it, and save and exit.
If you get an error toggle Secure boot mode to Custom and then to Standard.

KYHI said:

your reference to "UEFI" is actually called the 'BIOS"
(Basic Input Output System)

Click to expand...

For OP's benefit.

Actually, terminology gets a bit confused.

BIOS is strictly only applicable to older pre-UEFI pcs and you could only access it by various key functions e.g. f2 during startup.

With advent of UEFI, you do not actally use a traditional BIOS any more - you access the UEFI firmware and you can access it via Windows or some function key.

However, we (myself included) just tend to say "access the BIOS" regardless of whether PC is an old (legacy) BIOS pc or a newer UEFI pc.

It is just easier to lump them together and say "access the BIOS" rather than saying a mouthful like "access the BIOS for a legacy pc, or the UEFI firmware for a UEFI PC".

This explains it in more detail.

www.freecodecamp.org/news/uefi-vs-bios

For KevTech: Thanks KevTech. I had already used msinfo32 to make sure that I am using UEFI, and I definitely am.
I am aware that I can get into UEFI by hitting Del or F12 during POST. That's how I always use to do it.
However, It is now possible to enter UEFI when in Windows, and I have been doing just that for a short period.
It was when I changed CSM to disabled (prior to trying Secure Boot) that I found that I can no longer get into UEFI from within Windows. I can still do it by hitting Del or F12 at POST.
But, if I want to enable Secure Boot, I have to disable CSM. This would mean that in future I would have enter UEFI during POST.
Unfortunately, if I want to enable Fast Boot or Ultra Fast Boot (I do), the POST process is so quick that the logo screen is present for a fraction of a second, making it virtually impossible to access UEFI this way.
So, the question is, "Why does disabling CSM make it impossible to enter UEFI via Windows"? The only clue I have is that the motherboard LED displays Debug Code a6 when the screen goes blank, and a6 means "Detect and install all currently connected SCSI devices".
For cereberus; I'm glad that I'm not the only one that finds talking about UEFI to be a mouthful.

KevTech said:

CSM stands for compatibility support module.
It is an optional tool included in the UEFI firmware that allows legacy BIOS compatibility for older OS.
What does it say for bios mode in msinfo?
Start>run>msinfo32
If it says UEFI you are using UEFI.
If it says Legacy you are using the CSM module.
Try going into bios with Del or F12.
Next steps work better if you change them one at a time saving in between changing them.
Go to BOOT, disable 'CSM Support', 'Save and exit' and come back to the same BOOT menu. Now, go to 'Secure boot' and enable it, and save and exit.
If you get an error toggle Secure boot mode to Custom and then to Standard.

Click to expand...

For KevTech: Thanks KevTech. I had already used msinfo32 to make sure that I am using UEFI, and I definitely am.
I am aware that I can get into UEFI by hitting Del or F12 during POST. That's how I always use to do it.
However, It is now possible to enter UEFI when in Windows, and I have been doing just that for a short period.
It was when I changed CSM to disabled (prior to trying Secure Boot) that I found that I can no longer get into UEFI from within Windows. I can still do it by hitting Del or F12 at POST.
But, if I want to enable Secure Boot, I have to disable CSM. This would mean that in future I would have enter UEFI during POST.
Unfortunately, if I want to enable Fast Boot or Ultra Fast Boot (I do), the POST process is so quick that the logo screen is present for a fraction of a second, making it virtually impossible to access UEFI this way.
So, the question is, "Why does disabling CSM make it impossible to enter UEFI via Windows"? The only clue I have is that the motherboard LED displays Debug Code a6 when the screen goes blank, and a6 means "Detect and install all currently connected SCSI devices".

I can't talk about AMD boards, but on Intel boards in order to enable Secure Boot, you'll have to disable CSM. If not, no Secure Boot.

jameswesthead said:

Thanks Ghot, I have been doing just that. However, I would like to use Secure Boot, an that means I must disable CSM. Of course, I can always get into UEFI at POST time (but maybe not if I enable Fast Boot or certainly not if I enable Super Fast Boot).
Thanks KYHI. UEFI is the successor to BIOS, and my motherboard uses UEFI unless it s necessary for it to use BIOS for some OS other than Windows 11 - hence the CSM. setting I don't want it to use BIOS because I would like to enable Secure Boot, and it insists on UEFI only (i.e.CSM disabled)

Click to expand...

I have CSM enabled and Secure Boot.

Ghot said:

I have CSM enabled and Secure Boot.

Click to expand...

Yeah, I'm not sure that's possible but that's what you say, so....

It's also in line with what the OP posted about his AMD board, and which I agree.

Dru2 said:

Yeah, I'm not sure that's possible but that's what you say, so....

It's also in line with what the OP posted about his AMD board, and which I agree.

Click to expand...

I have an AMD board as well.
That's the way mine is set.

I don't use Bitlocker or any of that Security stuff, so that may make a difference, I don't know.
I just turned on fTPM and Secure Boot for Win 11.

OI had to turn on CSM to be able to set the Boot Device Control to UEFI.
Then I just left it enabled.





Just checked... CSM and Secure Boot are enabled.

BitLocker has zero to do with Secure Boot or CSM. It isn't even in the requirement chain. The fact that one uses or doesn't use BitLocker will not affect Secure Boot or CSM.

And I know what CSM is as I've delt with it years ago and why I understand it now. The only reason you'd need CSM enabled is for very old legacy hardware, especially with a GPU that doesn't support UEFI, which pretty much any GPU made within the last 10-15 years should.

Ghot said:

I have an AMD board as well.
That's the way mine is set.

I don't use Bitlocker or any of that Security stuff, so that may make a difference, I don't know.
I just turned on fTPM and Secure Boot for Win 11.

OI had to turn on CSM to be able to set the Boot Device Control to UEFI.
Then I just left it enabled.


View attachment 49717


Just checked... CSM and Secure Boot are enabled.

Click to expand...

My Gigabyte / AMD motherboard does not even display "Secure Boot" as an option, until CSM is enabled, so I suppose that it is the same as yours.

jameswesthead said:

My Gigabyte / AMD motherboard does not even display "Secure Boot" as an option, until CSM is enabled, so I suppose that it is the same as yours.

Click to expand...

That's exactly how my Intel Gigabyte boards work...

CSM Enabled...


CSM Disabled...

The whole BIOS / UEFI is something that confuse a lot of people. For example, I have an open case with a company that makes backup software (not Macrium!). This issue has been open for about a year and a half and their developers just can't quite seem to figure out some key differences between a legacy BIOS based system and a pure UEFI based system (no CSM).

For example, in UEFI mode, if you boot into Windows PE or Windows RE you MUST display at native resolution of the monitor. You cannot down-shift to a lower resolution like 1024 x 768 unless you enable CSM. Their software can't handle that, making their recovery media useless unless you enable CSM.

Naturally, some systems now designed for Win 11 have no CSM to enable.

Always a fun time!

hsehestedt said:

The whole BIOS / UEFI is something that confuse a lot of people. For example, I have an open case with a company that makes backup software (not Macrium!). This issue has been open for about a year and a half and their developers just can't quite seem to figure out some key differences between a legacy BIOS based system and a pure UEFI based system (no CSM).

For example, in UEFI mode, if you boot into Windows PE or Windows RE you MUST display at native resolution of the monitor. You cannot down-shift to a lower resolution like 1024 x 768 unless you enable CSM. Their software can't handle that, making their recovery media useless unless you enable CSM.

Naturally, some systems now designed for Win 11 have no CSM to enable.

Always a fun time!

Click to expand...

Thanks for that. I wonder whether the resolution of my monitor is set at native. I think it is.....

jameswesthead said:

Thanks for that. I wonder whether the resolution of my monitor is set at native. I think it is.....

Click to expand...

It's not really something you change on the monitor. Also, bear in mind that this is only something that affects WinPE and WinRE. Most programs handle it fine these days, although it was an issue in the early days, but back then every system had CSM that could be enabled.

hsehestedt said:

The whole BIOS / UEFI is something that confuse a lot of people. For example, I have an open case with a company that makes backup software (not Macrium!). This issue has been open for about a year and a half and their developers just can't quite seem to figure out some key differences between a legacy BIOS based system and a pure UEFI based system (no CSM).

For example, in UEFI mode, if you boot into Windows PE or Windows RE you MUST display at native resolution of the monitor. You cannot down-shift to a lower resolution like 1024 x 768 unless you enable CSM. Their software can't handle that, making their recovery media useless unless you enable CSM.

Click to expand...

I'm a bit confused how a backup issue can be linked to whether CSM is enabled or not. If you understand CSM, you'd know it's a compatibility switch to allow for old legacy hardware, in particular, for older GPUs that did NOT support UEFI. If you have a non-UEFI GPU, which you should not considering UEFI supported GPUs has been around the last 10-15 years, it will NOT work unless CSM is enabled. If you have a UEFI supported GPU, and fairly new hardware, there's no need to have CSM enabled.

Additionally, it is said (don't know, don't use it) that if using Legacy BIOS, CSM will also (must be) enabled. So, there's that.

Regardless, it has nothing to do with software, and I suspect the reason your issue has been open for a year is because there is no answer as CSM has nothing to do with backups.... unless the backup is affected by the GPU, where the GPU is not UEFI supported.

hsehestedt said:

Naturally, some systems now designed for Win 11 have no CSM to enable.

Click to expand...

That makes sense to me considering Windows 11's hardware requirements, which would make CSM useless.

Anyway, What Is CSM Support & Should I Enable It in BIOS? [Answered]

BTW, I had to deal with this whole CSM/UEFI mess some years back as Sapphire released a GPU, that was said to support UEFI, but didn't and subsequently caused me fits when trying to enable Secure Boot. That's how I was introduced to CSM. Any Sapphire eventually released a BIOS fix for the issue. Had a post on it. If I find it, I'll link.

hsehestedt said:

It's not really something you change on the monitor. Also, bear in mind that this is only something that affects WinPE and WinRE. Most programs handle it fine these days, although it was an issue in the early days, but back then every system had CSM that could be enabled.

Click to expand...

It is in native resolution (3840 X 2160), so thanks for responding. I still think that it is something to do with SCSI inititialisation, given the a6 led code (Detect and Install all currently connected SCSI devices) I get when the screen goes black and just sits there unresponsive.