Explanation for some code in int10

Explanation for some code in int10_modes.cpp?

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First post, by emendelson

Posted on 2013-07-23, 00:48

emendelson Offline

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I've been experimenting with custom video modes in int10_modes.cpp, but I don't fully understand all the items in the mode list. The first few lines look like this:

1/* mode  ,type     ,sw  ,sh  ,tw ,th ,cw,ch ,pt,pstart  ,plength,htot,vtot,hde,vde special flags */
2{ 0x000  ,M_TEXT   ,360 ,400 ,40 ,25 ,9 ,16 ,8 ,0xB8000 ,0x0800 ,50  ,449 ,40 ,400 ,_EGA_HALF_CLOCK	},
3{ 0x001  ,M_TEXT   ,360 ,400 ,40 ,25 ,9 ,16 ,8 ,0xB8000 ,0x0800 ,50  ,449 ,40 ,400 ,_EGA_HALF_CLOCK	},
4{ 0x002  ,M_TEXT   ,720 ,400 ,80 ,25 ,9 ,16 ,8 ,0xB8000 ,0x1000 ,100 ,449 ,80 ,400 ,0	},

I can figure out some of the abbreviations in the top row, but not all, and would be grateful for any help. Here's what I understand, more or less:

mode = mode number (of course)
type = text, graphic, etc.
sw, sh = width and height in pixels???
tw, th = width and height in columns and rows???
cw, ch = character width and height in pixels
pt = point size???
pstart, plength = start and length of BIOS region???
htot, wtot = ???
hde, vde = ???
special flags = self-explanatory

I would be very grateful for any clarification - or for a pointer of where to look for one. Thanks for any help.

Last edited by emendelson on 2013-07-23, 01:15. Edited 1 time in total.

Reply 1 of 5, by ripsaw8080

Posted on 2013-07-23, 01:13

ripsaw8080 Offline

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pt = page total (# of pages)
pstart = page start (linear address of first page)
plength = page length (page size)
htot,vtot = horizontal,vertical total (scan area)
hde,vde = horizontal,vertical display end (display area)

Reply 2 of 5, by emendelson

Posted on 2013-07-23, 01:16

emendelson Offline

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Perfect - thank you!

Reply 3 of 5, by emendelson

Posted on 2014-02-17, 01:33

emendelson Offline

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Sorry to come back to this thread after three years, but I wonder if anyone can explain how to determine the numbers for:

htot,vtot = horizontal,vertical total (scan area)
hde,vde = horizontal,vertical display end (display area)

Are these calculated from lines, columns, point size, etc., or must they be figured out by hand? I'll be very grateful for any help with this.

Reply 4 of 5, by ripsaw8080

Posted on 2014-02-17, 02:26

ripsaw8080 Offline

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The display end should be easy for your custom text modes, because generally: vde = sh, hde = tw

htot and vtot should each be larger than the display area (in pixels), with the extra representing overscan, retrace, and blanking. Together with clocking they determine the time taken to draw a line and the time taken to draw the full frame. Try to follow the example of existing modes, and you can use a debugger build to see the horizontal and vertical timings.

http://wiki.osdev.org/Video_Signals_And_Timin … lay_Composition

Reply 5 of 5, by emendelson

Posted on 2014-02-17, 02:54

emendelson Offline

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Thank you for that; that (and the link) explains everything I didn't know.

One more question: how important is it that htot and vtot are exactly right? Or (as it seems) is it all right to have a number that is large enough, even if it's larger than necessary?

Now it's time for me to make a debug build and figure out how to use it...

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