Unofficial documentation for
			the Screen Blaster 2 screen enhancer
			on Atari Falcon 030

			v 0.4 - 2003/09/26


0. Disclaimer
-------------

This document describes the Screen Blaster 2. This is an unofficial
document. The originals authors have nothing in common with this document,
except the involved product.

This document describes the Screen Blaster 2 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
---------------

Screen Blaster 2 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 sblaster.prg installs a new cookie, plus
some new vectors to setup enhanced video modes.


2. The cookie
-------------

Its name is 'OSBL', and is a pointer to a function, which is used to control
the ScreenBlaster.

There are 6 functions than can be called (numbered 0 to 5, which lies in
register D0 upon calling this function). The registers d3-d7/a2-a6 are
preserved.

2.1 GetPath()
--------------

Input: void
Output: A0 = pointer to the sblaster.inf path (Ex: 'c:\auto\')

2.2 GetModes()
--------------

Input: void
Output: A0 = pointer to current videomode infos in memory
		A1 = pointer to first videomode infos in memory

2.3 SetVideoMode()
------------------

Input: A0 = pointer to videomode infos in memory
Output: D0 = Screenblaster enabled status

2.4 GetStatus()
---------------

Input: void
Output: D0 = Screenblaster enabled status

2.5 SetVirtualScreen()
----------------------

Input: A0 = pointer to videomode infos in memory
Output: void

2.6 GetFile()
-------------

Input: void
Output: A0 = pointer to the sblaster.inf file in memory


3. XBIOS functions
------------------

Vsetscreen() is allowed to change physical screen address, but changing screen
mode is disabled. 
Vsetmode() return the current videomode.


4. Screenblaster sblaster.inf file
----------------------------------

First, you have a header:

typedef struct {
	unsigned char	id[24];	/* "OverScan Screenblaster" */
	unsigned short	dummy1
	unsigned short	mon_count;	/* Number of monitor's names */
	unsigned short	dummy2[3];
	unsigned short	mode_count;	/* Number of video modes */
	unsigned short	dummy3[10];
	unsigned short	clock;		/* External clock number */
	unsigned short	dummy4[5];
	unsigned long	mon_info[4];	/* Info for each type of monitor */
} sblast2_inf_header_t;

Then the monitor's names (mon_count times):

typedef struct {
	unsigned char	name[32];
} sblast2_name_t;

Then the video mode descriptions (mode_count times):

typedef struct {
	unsigned long	next;			/* Offset to next mode in memory, replaced
										by pointer in memory
										0xffffffff is last video mode */
	unsigned short	dummy1;
	unsigned long	offset_name;	/* Offset to video mode name, replaced by
										pointer to it in memory */
	unsigned short	virt_width;		/* Virtual width - 1 */
	unsigned short	virt_height;	/* Virtual height - 1 */
	unsigned short	phys_width;		/* Physical width - 1 */
	unsigned short	phys_height;	/* Physical height - 1 */
	unsigned short	dummy2[2];
	unsigned short	bpp;			/* Bits per pixel */
	unsigned long	colours;		/* Number of colours */
	unsigned short	pitch;			/* Length of line in bytes */
	unsigned short	dummy3;
	unsigned short	hfreq;			/* Horizontal frequency * 10 */
	unsigned short	vfreq;			/* Vertical frequency * 10 */
	unsigned short	dummy4[18];
	unsigned long	offset_regs;	/* Offset to video registers list, replaced
										by pointer to mode->num_regs in memory */
	unsigned long	dummy5;
	unsigned short	num_regs;		/* Number of video registers following */
	sblast2_reg_t	registers[];	/* Variable length array */
	unsigned short	dummy6[3];
	sblast2_name_t	name;			/* Name of video mode */
} sblast2_mode_t;

typedef struct {
	unsigned long	address;	/* Address of video register */
	unsigned short	value;		/* Value of video register */
} sblast2_reg_t;

-- 
Patrice Mandin <pmandin(at)caramail(dot)com>
http://membres.lycos.fr/pmandin/