flat assembler - Booting Characters

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smiddy

Joined: 31 Oct 2004
Posts: 557

smiddy 17 Dec 2014, 18:35

I have been trying to find a reference to boot process in particular the character sets used, and if I can influence it to be more than the 256 characters defined in ASCII character set. It appears there is a 512 character set, that can be programmed, but it got me to wondering, can you go to any of the UTF-XX character sets?

Has anyone here delved into this at all? What problems pitfalls, or goodness-es have you encountered?

I'd like to use a text mode, with characters I develop and use those in text mode, but I think there is a small problem in that the character is a byte, and the attribute is a byte, which doesn't leave room for multi-byte character sets, so how is that done, if at all?

As always, constructive thoughts are welcome.

Smiddy

17 Dec 2014, 18:35

BAiC

Joined: 22 Mar 2011
Posts: 272
Location: California

BAiC 18 Dec 2014, 00:35

there are only 3 scan code sets that I know of (raw data from keyboard). if you make a program like Windows' Character Map then you can generate a character set that's as large as you want (keyboard combos from the scan codes could be used as well).

it's mostly a software issue. that said; most people use a form of the UTF encoding scheme (which includes ASCII as a subset).

if you want arbitrary glyphs then you'll need one of the bitmap video modes. VGA Text Mode only supports 256 characters that I know of. if you change the VGA Text Font dynamically it'll change everything on screen rather than an individual character.

- Stefan

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18 Dec 2014, 00:35

neville

Joined: 13 Jul 2008
Posts: 507
Location: New Zealand

neville 18 Dec 2014, 03:36

smiddy, it might be worth reading up about code pages.

Later versions of M$-DOS could change character sets by loading code pages (usually .CPI files iirc). This is how non-English character sets were set up. The standard English/American character set was code page 437.

Although only 256 characters (and 256 attributes) could be defined at one time, it was possible to produce "pseudo-graphical" user interfaces in text mode using graphics characters.

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18 Dec 2014, 03:36

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr 18 Dec 2014, 03:58

smiddy,

VGA uses bit 3 of attribute byte to select one of character definition tables designated by two fields in Sequencer Character Map Select register (3C4/5[3]), along with foreground color. Thus you can display 512 different shapes simultaneously in text mode (probably halving foreground color palette).

18 Dec 2014, 03:58

smiddy

Joined: 31 Oct 2004
Posts: 557

smiddy 18 Dec 2014, 04:12

baldr wrote:

smiddy,

VGA uses bit 3 of attribute byte to select one of character definition tables designated by two fields in Sequencer Character Map Select register (3C4/5[3]), along with foreground color. Thus you can display 512 different shapes simultaneously in text mode (probably halving foreground color palette).

Yeah, I found this and it is enticing, which I will likely use. The use of the third bit remove the high intensity bit functionality the way I understand it.

From your put, I would like to try to do something like Norton used to do for DOS, way back in the day, use the regular set, and then use the secondary set for the glyphs, if that is what they did, I'm not convinced their mouse driver wasn't actually a VGA graphics mode using a combination of drawing and text and glyphs.

neville, I believe OS/2 had a similar scheme too, I'll give that a read.

18 Dec 2014, 04:12

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20433
Location: In your JS exploiting you and your system

revolution 18 Dec 2014, 06:45

smiddy wrote:

I would like to try to do something like Norton used to do for DOS, way back in the day, use the regular set, and then use the secondary set for the glyphs, if that is what they did ...

IIRC it was simpler than that: they just used four characters out of the base 256 set and rewrote those four on the fly to show the cursor.

18 Dec 2014, 06:45

smiddy

Joined: 31 Oct 2004
Posts: 557

smiddy 18 Dec 2014, 12:12

revolution wrote:

smiddy wrote:
I would like to try to do something like Norton used to do for DOS, way back in the day, use the regular set, and then use the secondary set for the glyphs, if that is what they did ...
IIRC it was simpler than that: they just used four characters out of the base 256 set and rewrote those four on the fly to show the cursor.

Everything I keep finding says that, and that makes sense too, a character to screen translation. If I can use another 256 characters I can do even more, making a set of characters that boundaries and buttons for the interface.

18 Dec 2014, 12:12

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr 18 Dec 2014, 18:22

smiddy,

There is small quirk in 9-dot A/N modes: ninth column of character cell is either blank or copy of eighth (for codepoints 0xC0…0xDF which usually contain line drawing glyphs). This behavior is controlled by Enable Line Graphics bit in Attribute Mode Control register of Attribute Controller (0x3C0/1[16], bit 2).

18 Dec 2014, 18:22

smiddy

Joined: 31 Oct 2004
Posts: 557

smiddy 18 Dec 2014, 18:31

Thanks for the heads up!

18 Dec 2014, 18:31

smiddy

Joined: 31 Oct 2004
Posts: 557

smiddy 18 Dec 2014, 18:35

http://www.osdever.net/FreeVGA/vga/vgatext.htm

18 Dec 2014, 18:35

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8357
Location: Kraków, Poland

Tomasz Grysztar 18 Dec 2014, 18:45

I did play with the character glyph definitions a lot when I learned assembly language back in the DOS days. Too bad my early programs did survive only in a binary form. My font editor used the VGA's feature of using two fonts at once so that you could see the entire font you edited and at the same time still have an UI using regular font.

18 Dec 2014, 18:45

smiddy

Joined: 31 Oct 2004
Posts: 557

smiddy 18 Dec 2014, 19:32

Kewl, thanks! I will model it after this, nice. Too bad you don't have the sources though... Smile

EDIT: I really like the scribble font!

18 Dec 2014, 19:32

smiddy

Joined: 31 Oct 2004
Posts: 557

smiddy 19 Dec 2014, 23:35

Tomasz

Do you happen to recall the *.f16 format?

8 x 16 bits per character = 128 bits/character = 16 bytes/character

16 bytes/character x 256 characters = 4096 bytes

That appears right, but want to be certain. Offset 0 in *.f16 is the offset of the indexed character at 0, correct, and the rest follow suit?

I am going to try to use a secondary font shortly after I edit a font to use for a TUI using your tool (which I will model later).

Smiddy

19 Dec 2014, 23:35

smiddy

Joined: 31 Oct 2004
Posts: 557

smiddy 20 Dec 2014, 03:23

Yep, 8 x 16, got it working fairly quickly in DOS, using ports (mainly). Kewl! I used Tomasz's scribble.f16 as the second font.

I need to figure out how to turn off the intensity for the second font, but this is a decent start. Ignore the carriage return and line feed, I will filter those out of my routine later.

Description:
Filesize:	38.86 KB
Viewed:	14138 Time(s)

20 Dec 2014, 03:23

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr 20 Dec 2014, 17:21

smiddy wrote:

I need to figure out how to turn off the intensity for the second font

There are several ways to achieve that effect. You may copy lower half of palette into higher, or mask out that bit using Color Plane Enable register of Attribute Controller (0x3C0[18], bit 3).

20 Dec 2014, 17:21

smiddy

Joined: 31 Oct 2004
Posts: 557

smiddy 20 Dec 2014, 18:02

baldr wrote:

smiddy wrote:
I need to figure out how to turn off the intensity for the second font
There are several ways to achieve that effect. You may copy lower half of palette into higher, or mask out that bit using Color Plane Enable register of Attribute Controller (0x3C0[18], bit 3).

Thanks! I haven't studied all the registers yet, however I was looking for intensity to no avail. Color Plane seems an area I didn't consider. Again, thanks!

Smiddy

20 Dec 2014, 18:02

bubach

Joined: 17 Sep 2004
Posts: 341
Location: Trollhättan, Sweden

bubach 15 Jan 2015, 17:53

You should try the fontman DOS program (try running in dosbox) it allows loading and editing of DOS font files and will also show all the characters in the default font.

http://sta.c64.org/dosprg/fpman220.zip

This is how I modified the standard font for the first DexOS version to include a logo instead of all those UI -like lines. Wink

If you want to support proper UTF-8 in text mode I would probably suggest you do VGA mode 12h (640x480px with 12 colors) or possibly even VESA instead and emulate text mode, giving you full pixel freedom to make any font you like.

But as previously stated, you could with some trickery get 512 chars at the same time, which would be enough for most situations, if you modify the fonts on the fly depending on what is showed on screen - you could potentially have a much larger set of characters to choose from then 512 in the "virtual font".

Description:
Filesize:	114.26 KB
Viewed:	14103 Time(s)

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15 Jan 2015, 17:53

smiddy

Joined: 31 Oct 2004
Posts: 557

smiddy 15 Jan 2015, 18:46

Kewl, I'll take a look when I get home. Tom posted his too, which works nicely as well.

I will eventually use VGA and/or VESA and/or card specific so I can use the entire screen on flat panel. I don't know that standard VGA and VESA can/will do a 16:9 screen ratio with text. I need to do further research on that.

Then again, I am working memory implementations at the moment, then floppy/hard disk controllers. Smile

Then at some point my TUI. LOL!

Smiddy

15 Jan 2015, 18:46

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