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*		Backward, the ST emulator for FALCON O3O		*
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|V 1.30|
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 I)		Introduction.
 II)		Inventory.
 III)		How to run Backward.
 IV)		Backward's options.
 V)		Tips.
 VI)		Notes.
 VII)		Technical explaination.
 VIII)		Future improvements.
 IX)  		Address.
 X)		Backward history.
 XI)		Thanks.
 XII)		Bugs report.


I) INTRODUCTION :

	Since most of FALCON's owners are former ST's owners (and sometimes
still ones, like me), they want their ST games to run on the FALCON. Yes, but
if the GEM compatibility is good enough for as much as 90% GEM programms, 
hardware differences prevent about 80% games to work. That's why I created 
Backward. It is supposed to handle hardware differences so that good old 
games can still run. So far I tested it, it has offered me something like 75% 
compatibility. I hope you enjoy it as much as I do.



II) INVENTORY :
	With the backward package file you must found :
	 - READ_ME.TXT 			file, this one.
	 - BACKWARD.PRG			the program itself.
	 - BACKWARD.RSC			its ressource file.


III) HOW TO RUN BACKWARD :
	First, you'll have to run it on a FALCON with at least 4 Megs
(simple no ?). Use a video mode that offers at least 16 colors. 
Double click on BACKWARD.PRG. You reach than a dialog box with three choices:
- Information 	: Click on it and you'll see.
- Set Up	: Access to the configuration's dialog box.
- Quit		: Leave Backward.

	Click on Set Up to choose configuration (it will be explained later
 in this text) then choose a boot mode :
- Boot now	: Run immediatly a ST disk.
- Set up now	: Configure Falcon with curent choices.
- Quit		: Back to first box.

	If you select [Set up now] then [Quit], your Falcon will be configured
accordingly to the options selected.

	If you select [Boot now], an alert box will give a last chance to
refuse. REMOVE now ANY DISK which stands in the floppy DRIVE.

	If you continue onward, your FALCON will reboot. The ATARI logo will 
appear after a few seconds. Then your drive led will flash once, you have 
now to keep pressed ALTERNATE until the BACKWARD infos come on screen.
	Backward tells you the options selected and the operations it has
undertaken. You can now INSERT YOUR DISK. Press a key. That's all.


IV) BACKWARDS OPTIONS :

	This dialog box allows you to alter the FALCON set up. Feel free to 
try as many configuration as you want when attempting to run a programm.

	Each option will now be explained with advice to know when it have
to be selected.

- 68O3O Frequency : This option allows you to slow down the microprocessor
		down to 8 Mhz. It should be use when games run to fast, or
		for some disk protections that refuse to run.
		NOTE : this option has little effect on compatibility, so
		keep your 68O3O at 16 Mhz and enjoy light speed !

- Blitter Frequency : This option allows you to alter Blitter Frequency. I
		don't think it changes anything for compatibility, but it
		offers you another way to slow down your computer.

- Instruction Cache : With this option you can turn Instruction Cache off.
		This a great incompatibility cause for demos and disk
		protection. But it seems that some FALCON TOS turn this
		cache on whatever you do !

- Speaker : With this you can turn the internal speaker on/off
		( I must admit I have decided to unplugged it).

- Ram Size : I don't think you'll need a lot of explaination for this one.

- DMA sound interrupt : This should select Timer A pin or MFP input port 7 pin
		for sound interrupt.If you haven't any sound with a program
		or the sound begin then stop, try alter this option.

- Bus error : This is the most important option I think. Due to hardware
		differences beteween ST and  FALCON, access to the ST
		sound processor (YM 2149) may cause Bus error. So you can :
			- Left : don't do anything when it happens.
			- Corr. : this is the best handling mode so far.
			When it's selected, Backward will attempt to
			modify programs which cause errors. May doesn't work
			with some programs.
			- Simul. : correct the access to the YM2149, the 
			middle choice but it slows everything down a bit.
		If your programm cause a bus error (two bombs!), it's may
		be because of the YM2149 access. So try the Corr. choice.
		If it still crashes, select Simul.


- Advanced Options : This one let you access to another panel which offer
		more options. You don't have to use them in normal case.
		They are :
			- Move Exception Table : Normally on. Moving
		exception table prevents programs to disable my own
		error-handling routines, but it slows down the computer
		a little bit. If your program seems not to like it
		(very bugged sounds, flashing colors...) turn it off.
			- Emulate Line F calls : let my routine
		emulate some Line F calls. Use it when the programm show
		11 bombs.
			- Move Pmmu's Tree : Well there is absolutly no
		reason for you to turn it off. Try it as a last solution.
			- Emulate St Ram Bug : Accessing a memory space
		where nothing was connected (no RAM, no chips' register)
		had no effect on a ST. It's no longer the case. Use it
		when your programm doesn't work. WARNING : Simul., correc.
		YM access won't work anymore with this option turned on, 
		YM access will be skipped (it means disturbed digisound).
			- Data Cache : Normaly on, turn it off as a last
		solution (effects of Data Cache are uneasy to see).

	The last options will be implemented in the future, so are *not*
	useable.


V) TIPS:
	In most cases you won't have to alter any option because they're
already set for a good compatibility.

a) Best compatibility:
	- Turn 68030 and Blitter to 8Mhz.
	- Turn both caches (instruction and data) off.
	- Keep pmmu's tree moved away.
	- Turn ST RAM Bug on (sorry that mean bad sound).
	- Don't care for Bus error (due to ST RAM bug).
	- Select 1 Meg (some old games may require 512K).
	- Turn Line F calls on.
	- Try each Interrupt source for DMA sound if there's still nothing.
	
b) How to decide configuration:
	- First of all, it's a game written before 1989 (before STE), and
	it use>s digisound -> Use corrected YM Access.
		Then :
		- it's allright. Nothing to do.
		- The game slows too much or it stops -> try simulated
		access and if it's inneficient - >disable Exceptions move.
	(you may recognize such games because they show 2 bombs).

	- The game has been written after 1989 and YM access options don't
	let the game keep running -> alter DMA sound interrupt.
	(such games may have a bit of music before silence, or a long
	whistle).

	- The game shows 11 bombs ->select Line F calls.

	- The game does *not* load itself-> turn 68030 to 8Mhz
		If there are still problems -> turn on ST RAM Bug.

	- There are still problems, try the Best Compatibility set up.

VI) NOTES:

 - Booting with Backward will cause a cold reset (power on) on the next restart
 	to let the Falcon reconfigure itself.

 - Memory Size and Bus handling have effects only if you select [Boot Now].
 	I may change it a day, but I'm tired.

 - As said before, Cache option may have no effect.

 - You may keep the Harddisk boot (by *not* pressing alternate key), but
 	most of the time, harddisk is a major cause of incompatibility.


VII) TECHNICAL EXPLAINATIONS :
	- Frequency configurations are made throught an undocumented address,
 so Backward may not work on future FALCONs. I refuse to give this address (you
 can still disassemble BACKWARD to see) because it's undocumented, it should
 be used only for emulations, no for special FXs or anything else.
	- Backward was written using DEVPAC ST II.
	- YM corrected access option uses TRAP call (#3 to #10).

VIII) FUTURE IMPROVEMENTS:
	- Old screen base compatibility : the memory space used by the screen
	has been moved since ST, some programs don't like this.
	- Disable YM : no sound at all, but no more problem for it neither.
	- Improved memory configuration.
	- Handling routines for TOS changes.

This improvements will be done only if this program is satisfying.So please
send donations or appreciations. Donators will be registered users and
they'll get the latest version of Backward.


IX) ADDRESS:
	You may send any donation, advice, question, bug reports etc...
to this adress:

	Mr Cyrille Dupuydauby

	53 domaine des aigles
	60500 Chantilly
	FRANCE

				See you soon for V1.40.


X) BACKWARD HISTORY:

- Idea : 5 april 1993.
- beta version : 10 april 1993.
- V 1.00 running : 12 april 1993.
- V 1.10 running : 16 april 1993.
- V 1.20 running (first release) : 21 April 1993.
- V 1.30 running : 28 april 1993.

XI) THANKS :
	Thanks are sent to Mathias AGOPIAN, who's article help me a lot
to improve BACKWARD (essentially moving PMMU and Blitter frequency).
	Thanks to the Falcon for the still unused soundtrack and the
 uploading.

XII) BUGS REPORT :
- Setting DMA Sound Interrupt Timer A may had no effect in V1.20. It's
corrected since V1.30.
- Turning off DATA cache hadn't any effect.Corrected since V1.30
- 512 Ko Option doesn't work. It seems that the Falcon refuses to run with
so little memory. Not yet corrected (if ever).
