SOLVED: Problem with Asus Prime X299-A UEFI BIOS

[Bill Anderson]

I'll post this even though I'm not convinced anybody who can use the
info will ever find it here. It's just that I've received so much good
info in this newsgroup over the years (primarily from Paul) that I want
to give back if I can.

My problem was that I'd installed three versions of Win10 on my new
Prime X299-A setup and when I'd choose something other than my default
OS using F8, all the boot options (OSs and optical drive) would get
scrambled in UEFI BIOS. Once I'd picked an alternative OS using F8, I
never could be sure exactly what OS I'd get upon reboot. (I don't use
Boot Manager, want never to see it.)

I explained this problem today to a tech via the Asus website chat
feature and this is how he replied:

This should do it:

1. Disconnect all the other drives from the unit leaving only the main
boot drive.
2. Go to BIOS and under boot then go to OS type and set it as Windows OS.
3. Disable Launch CSM.
4. Save and Exit the and this should lock it as the boot device.

After this you can add back the other drives and try the F8 option and
see if it fixes the issue.

Yes, I had to do a little investigative digging to find a way to set OS
type as Windows OS, cuz the option wasn't exactly where he said it would
be, but that's OK. Bottom line is that this worked: Now I can pick the
OS I want by using F8 without worry.

And the takeaway is that Asus Tech Support came through for me on the
first try. Yay!

--
Bill Anderson

I am the Mighty Favog

[Paul]

I find

powercfg /h off

works for me. This prevents both hibernation and Fast Start,
so that the BIOS F8 selection process will be an honest one.
I can leave CSM enabled.

Of course, if you're a big hibernation person, that'll be
an issue for you.

EasyBCD could be used to add the other OS drives, then leave
the BIOS configured to boot the "boss" drive. But that doesn't
cover every usage scenario, so won't keep everyone happy.

UEFI has a relatively large NVRAM storage facility. Likely
using the BIOS Flash chip for the actual storage. It can
memorize environment variables. By comparison, traditional
BIOS only have the 256 byte CMOS storage. And using CSM mode
is an emulation of a traditional BIOS.

Intel has declared CSM to be a dying feature, so
in a few years, motherboards will be UEFI only.
We'll have to wait and see, as to whether the rest
of the industry agrees.

Paul

[Bill Anderson]

I think I'm about to learn something basic.

I don't understand how making an adjustment in Windows can have an
effect on which of three Windows installations BIOS chooses to boot
from. Isn't the choice made prior to the computer seeing anything in
Windows?

I do know that when Windows is installed using UEFI, I don't choose an
actual HDD/SSD using F8, even though F8 lists them as choices. Instead
the choices that work are all labeled "Windows Boot Manager" followed by
the physical location of the installation. It's easy enough to identify
the drive I want that way. But it's obvious UEFI/BIOS knows it's
looking at Windows installations, so maybe it's picking up some Windows
data even prior to booting from a particular drive?

And if I tried your suggestion, wouldn't I have to make the same entry
in all three Windows installations?

[Paul]

It's possible our UEFI BIOS are designed differently.

Mine never makes a reference to Windows Boot Manager.
Maybe it would if I was in pure UEFI mode.

The F8 boot menu only lists drives. It also puts
a modifier to indicate whether the drive is
to be booted CSM or UEFI. A drive can be listed
twice for example. I have some OSes on USB sticks
that show up this way (because they're hybrids).

UEFI WDC2004
CSM WDC2004

And if I want it to start in legacy BIOS CSM mode, I
cursor down to the second entry.

Some devices are only listed once, some are listed
twice, according to what the BIOS thinks it "smells"
on the device. For example, a Win10 Hybrid DVD supports
both boot modes, so you would expect the optical drive
to be listed twice in the F8 menu.

If you set the boot order in the BIOS, and *don't*
use the F8 boot menu, my presumption is you set
the "boss" drive in the BIOS. Then, using EasyBCD,
you edit the boot menu of the "boss" drive so that
it shows the other two drives and the single OS
on those drives. Now, the "boss" drive has three
disks mentioned in its BCD (boot menu). Without
pressing F8, Win10 comes part-way up, and presents
the boot menu, with three items. I cursor to the
disk I want, and it restarts and selects that disk
with no further fuss.

When a Windows disk uses a hibernate function
(either Fast Start or Hibernate), the hibernate bit
is set in the chipset. When the BIOS comes up, instead
of "considering" the boot order, offering the user
the usual choices, the BIOS knows the last session
hibernated something. So the BIOS ignores the pressing
of F8 and Del, and just boots into the drive that
was hibernated. You can stop that by killing the power
for a bit, then powering up.

This is why I use "powercfg /h off", so that
all OSes have any hibernation-like functions turned
off. This ensures my F8 menu works. It ensures I
have control over selecting the next boot device.

Since the Asus guy gave you a method that works,
I've got no argument with that. It's just another
way to do things.

While I've done UEFI mode experiments, all my
daily driver configs are CSM. It's part of my
"Paul hates surprises" policy :-)

Paul