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VBE 81ffh in assembly

Posted: Thu Nov 22, 2018 11:30 am
by CheeseBees
Can it be used in assembly(im using nasm), and if so how?(in terms of values to set for it)

--EDIT--
can it be used to write to the memory

Re: VBE 81ffh in assembly

Posted: Thu Nov 22, 2018 11:44 am
by Octocontrabass
When you say "VBE 81ffh", are you referring to VBE mode 0x81FF?

Why do you want to use it?

What mode is the CPU in when you're trying to use it?

Re: VBE 81ffh in assembly

Posted: Thu Nov 22, 2018 11:46 am
by CheeseBees
Octocontrabass wrote:When you say "VBE 81ffh", are you referring to VBE mode 0x81FF?

Why do you want to use it?

What mode is the CPU in when you're trying to use it?
1. Yes i am
2. To get full access to my video ram as the mode description says its for
3. Real mode

Re: VBE 81ffh in assembly

Posted: Thu Nov 22, 2018 12:08 pm
by Octocontrabass
CheeseBees wrote:2. To get full access to my video ram as the mode description says its for
Why do you want to do that?
CheeseBees wrote:3. Real mode
You can use this function to get information about the VBE capabilities, this function to get information about the mode you want to use, and this function to set the mode. If VBE 2.0 is supported, you'll probably want to set bit 14 in the mode number (0xC1FF instead of 0x81FF) to use a linear buffer.

I suggest also looking at the VBE specification for the definitions of those functions, since it explains the requirements for calling each, and what the return values mean.

If you're writing a quick proof of concept, you can skip the check for VBE 2.0 since all recent VBE implementations support it.

Re: VBE 81ffh in assembly

Posted: Thu Nov 22, 2018 12:22 pm
by CheeseBees
Octocontrabass wrote:
CheeseBees wrote:2. To get full access to my video ram as the mode description says its for
Why do you want to do that?
CheeseBees wrote:3. Real mode
You can use this function to get information about the VBE capabilities, this function to get information about the mode you want to use, and this function to set the mode. If VBE 2.0 is supported, you'll probably want to set bit 14 in the mode number (0xC1FF instead of 0x81FF) to use a linear buffer.

I suggest also looking at the VBE specification for the definitions of those functions, since it explains the requirements for calling each, and what the return values mean.

If you're writing a quick proof of concept, you can skip the check for VBE 2.0 since all recent VBE implementations support it.
Thank you so much that just ended 2 years of searching.

Re: VBE 81ffh in assembly

Posted: Sat Dec 29, 2018 3:46 am
by bigboyav
Check out the below link, very detailed on how to use VESA Bios Extensions (VBE).

viewtopic.php?f=2&t=30186