Unofficial documentation for
			the Videl Inside 2 screen enhancer
			on Atari Falcon 030

			v 0.1 - 2003/01/31


0. Disclaimer

This document describes the Videl Inside cookie. This is an unofficial
document. The originals authors have nothing in common with this document,
except the involved product.

This document describes the Videl Inside cookie as the author understands it.
While every effort has been made to ensure that the contents of this document
are accurate, the author does not guarantee that any portion of this document
is actually correct. In addition, the author cannot be held responsible the
consequences of the any use or misuse of the information contained in this
document. 


1. Introduction

Videl Inside is a screen enhancer for Atari Falcon 030 computers. It can use
standard Videl (Atari Falcon video chip) clocks of 25 MHz, 32 MHz and external
clock to generate video modes.

When run from the AUTO folder, the vi2.prg installs a new cookie, plus
some new vectors to setup enhanced video modes.


2. The cookie

Its name is 'VI-2', and is a pointer in memory to the following structure.

typedef struct {
	unsigned short	version;
	unsigned short	length;
	unsigned short	dummy;
	vi_mode_t	vi2infmode;
	void		(*setmode)(vi_mode_t *newmode);
} vi_cookie_t;

'version' is the version of Videl Inside (0x0204 for 2.04).
'vi2infmode' is the mode loaded from vi2.inf file, for the current monitor.
'setmode' is a pointer to a function to setup a video mode.


3. The video modes file, <bootdrive>\vi2.dat, the header

This file contains all defined video modes. It has an header, followed by
video modes definitions.

typedef struct {
	unsigned char	name[8];	/* "DATFILE\0" */
	unsigned short	version;	/* 0x0103 */

	unsigned short	freqh_mini;	/* Freq limits for a multisync monitor */
	unsigned short	freqh_maxi;	/*  The freqh stored are divided by 100 */
	unsigned short	freqv_mini;	/*  The freqv stored are multiplied by 10 */
	unsigned short	freqv_maxi;
	unsigned short	multisync;	/* Multisync monitor ? */

	unsigned short	num_modes;

	unsigned short	intfreq1;	/* 25 MHz as default */
	unsigned short	intfreq2;	/* 32 MHz as default */
	unsigned short	extfreq;
} vi_header_t;

So you have an ident value (field 'name', followed by its version (0x0103) for
version 1.03.

Then you find frequencies limits for a multisync monitor, and the associated
flag (0=no, 1=yes) telling if these values are defined or not.
Note: here and in the video mode structure, the horizontal frequency is divided
by 100, and the vertical frequency is multiplied by 10.

You then have the number of video modes defined in the file, and the videl clock
frequencies for the video modes (these are divided by 100000: i.e. you have 250
for 25MHz).


4. The video modes file, <bootdrive>\vi2.dat, the video modes

Following the header, you will find vi_header_t->num_modes structures of this
type:

typedef struct {
	unsigned short	modecode;	/* Video mode definition */
	unsigned short	freqh_div;	/* Horizontal frequency divisor */
	unsigned short	width;		/* Horizontal resolution */
	unsigned short	dummy2;
	unsigned short	freqv_div;	/* Vertical frequency divisor */
	unsigned short	height;		/* Vertical resolution */
	unsigned short	dummy3[19];
} vi_mode_t;

'modecode' is defined as follows:
	bit 1: interlaced mode
		0=no, 1=yes
	bits 3,2: videl clock predivisor
		0=divide by 4
		1=divide by 2
		2=divide by 1
	bits 6,5,4: bits per pixel
		0=1 bpp
		1=2 bpp
		2=3 bpp
		3=4 bpp
		4=16 bpp
	bits 8,7: videl clock
		0=internal 1
		1=internal 2
		2=external
	bits 11,10,9: index value for 0xffff8266 register

'width' and 'height' are the resolution of the video modes. 'freq[v|h]_div' are
used to calculate the horizontal and vertical frequency of the video mode, given
the videl clock used.

- Example for a standard VGA mode:

hfreq_div=512, vfreq_div=520
bits 3-2 (predivisor)=01 and bits 8-7 (clock)=01

videlclock = internal2*100000 = 32 MHz
hfreq=videlclock/(hfreq_div<<(2-prediv))= 31250 Hz
vfreq=hfreq/vfreq_div = 60 Hz


4. The info file, <bootdrive>\vi2.inf

This file just has the video mode to select when entering GEM mode.
It holds place for 3 modes: monochrome, tv/rgb and vga.

typedef struct {
	unsigned char	name[8];	/* "VI2.INF\0" */
	unsigned short	dummy;
	viinfo_mode_t	videomode[3];
} viinfo_t;

The 3 video modes are stored with this structure:

typedef struct {
	unsigned short	dummy;
	unsigned short	mask;
	unsigned short	videomode;
	unsigned short	width;
	unsigned short	height;
	unsigned short	values[8];
	unsigned char	name[36];
} viinfo_mode_t;

'num_mode' is the number of the video mode in the vi2.dat file.
'mask' is 0x019f, a mask for the current Vsetmode(-1).
'videomode' is the nearest Falcon videomode code, to ease setup the video mode.
'values' are fields needed to setup the video mode.
'name' is the name of the video mode.

000a:	0008
000c:	019f	; video mode mask
000e:	010a	; Nearest Falcon video mode
0010:	0280	; 640	= width
0012:	01f0	; 496	= height
0014:	0032	; 50
0016:	0032	; 50
0018:	0026	; 38
001a:	0320	; 800
001c:	0280	; 640
001e:	00a4	; 164
0020:	0111	; 273
0022:	01f0	; 496
0024:	0015	; 21
0026:	name of video mode

5. Get current video mode

- TODO -


6. Setting a video mode

- TODO -

-- 
Patrice Mandin <pmandin@caramail.com>
http://membres.lycos.fr/pmandin/