OSDev.org

The Place to Start for Operating System Developers
It is currently Wed Jun 20, 2018 12:11 am

All times are UTC - 6 hours




Post new topic Reply to topic  [ 2 posts ] 
Author Message
 Post subject: Other VESA graphic modes.
PostPosted: Mon Jun 04, 2018 4:50 am 
Offline

Joined: Sun Apr 30, 2017 7:19 am
Posts: 1
Hello,
I achieved VBE VESA in my operating system. I init VBE from syslinux and then enable it but I have a problem, only some modes seems supported. For exemple I can't get 1366*768 working, on the net there is like nothing about this VESA mode..
If you have ideas thanks for your help!


Top
 Profile  
 
 Post subject: Re: Other VESA graphic modes.
PostPosted: Mon Jun 04, 2018 2:46 pm 
Offline
Member
Member
User avatar

Joined: Sat Jan 15, 2005 12:00 am
Posts: 8383
Location: At his keyboard!
Hi,

valentinbreiz wrote:
I achieved VBE VESA in my operating system. I init VBE from syslinux and then enable it but I have a problem, only some modes seems supported. For exemple I can't get 1366*768 working, on the net there is like nothing about this VESA mode..
If you have ideas thanks for your help!


The list of supported VBE modes comes from a table the manufacturer compiled into the ROM, where the manufacturer has no idea what kind of monitor will be attached and doesn't have an infinite amount of space for a huge number of video modes. The end result is that usually the list only contains the most common modes (and may not contain less common modes like 1366*768).

Also note that once upon a time (for VBE 1.0 and VBE 1.2) there were "VESA defined mode numbers" where VESA would say (e.g.) "mode 0x113 is 800*600 with 32768 colours". This was deprecated in 1994 (when VBE 2.0 was released), no new "VESA defined mode numbers" have been defined since 1994, and software should have stopped using "VESA defined mode numbers" in 1994.

Sadly some shrink wrapped third party boot loaders still to use these "deprecated 24 years ago" VESA defined mode numbers, rather than (e.g.) using something like "vga = 1366x768, bits=24, rate=60Hz" and searching for whichever mode is the closest match. In this case, even if you're lucky and the video card's VBE does include a less common video mode, you still won't be able to ask the boot loader to set that mode.

Finally; for cases where its impossible to know anything about all the different computers that the OS could be booted on (generic OS installer, "Live CD", ...) the idea of requesting a specific mode is broken (unless it requests the old "VGA 640*480 @ 60 Hz", which was defined as a "VESA safe mode timing" and should be supported on all PCs and monitors). Ideally; for these cases you'd have code that auto-selects the best video mode (to suit the OS, the video card and the monitor); and if you have code that does "hassle-free video mode auto-selection" well, then you can use it for all cases (including when the OS is installed on a specific computer and the user guarantees they will never upgrade their video card or monitor).


Cheers,

Brendan

_________________
For all things; perfection is, and will always remain, impossible to achieve in practice. However; by striving for perfection we create things that are as perfect as practically possible. Let the pursuit of perfection be our guide.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 2 posts ] 

All times are UTC - 6 hours


Who is online

Users browsing this forum: No registered users and 5 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group