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piotr5
Tux's lil' helper
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Joined: 14 Dec 2012
Posts: 101

PostPosted: Sun Feb 08, 2015 7:24 pm    Post subject: avoiding flickering screen on startup? Reply with quote

as I understood the purpose of framebuffer is to avoid screen turning black because of video-mode changes during startup.
crt and similar screens will flicker, which is even more annoying.
however on startup video-mode change happens 3 times:
first when grub2 starts and chooses the svga mode.
next when linux starts and switches to the vga-mode selected through vga= option
then a 3rd time as the init system takes over. (no systemd here.)

any idea how to force grub2 to choose the same mode as kernel?
seems videoinfo command on grub2 prompt doesn't know of that mode. different driver. also the other way around, kernel doesn't know of the svga mode.
guess I need to tell grub not to toy with video-modes at all, unless submenus are opened. are there any other options? nouveau module for grub?

any idea how to let the kernel do whatever the init system is doing for fonts and such?
do I need to compile the chosen fonts into the kernel to avoid the 3rd flickering?
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Roman_Gruber
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Joined: 03 Oct 2006
Posts: 3806
Location: Austro Bavaria

PostPosted: Sun Feb 08, 2015 7:26 pm    Post subject: Reply with quote

AFAIK there is a hole section in the kernel about the display.

How it is used and configured.

grub 2 => c => interactive shell => enter the command vbeinfo

There you will see a full list where you get the supported modes.

For the other init stuff you need to be more specific what you use and check the docs for that.

Quote:
first when grub2 starts and chooses the svga mode.

You need to adapt grub configuration file accordingly


""grub2.cfg"" e.g.

Quote:
function load_video {
insmod vbe
insmod vga
insmod video_bochs
insmod video_cirrus
}


you may adjust these
Quote:
set gfxmode=auto
load_video
insmod gfxterm


E.g Working example

Quote:
grep gfx /boot/grub/grub.cfg
set gfxmode=1920x1200x32
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piotr5
Tux's lil' helper
Tux's lil' helper


Joined: 14 Dec 2012
Posts: 101

PostPosted: Mon Feb 09, 2015 10:11 am    Post subject: Reply with quote

grub2 has no command called "vbeinfo" according to docs, only "videoinfo".
and as I said, videoinfo reports mode 0x11a for the 1280x1024 mode of my choice. if I choose that I get 80x25 text in linux.
and the other way around, to get 1280x1024 I must add "vga=0x317" to the kernel command line. it isn't listed by videoinfo.
you know of any way to tell grub2 to enter that videomode directly before the kernel does?
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Roman_Gruber
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Joined: 03 Oct 2006
Posts: 3806
Location: Austro Bavaria

PostPosted: Mon Feb 09, 2015 11:47 am    Post subject: Reply with quote

sigh.

grub2 here and it works and i gave you a working example of my box and even tested it. I was curious yesterday so I adjusted mine. and that grub2 lines i gave you are from linux mint 11 which is aka ubuntu and was autogenerated as i installed linux mint 11. therefore it exists

well when you claim that i am wrong, i can not offer you any more advise, i am sorry.

you can use vbeinfo and videoinfo in the build in shell of grub2. and both work here

vbe vesa bios extension afaik, wikipedia
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