Getting started
Assembly language, in Devpac, Tutorial
by
John Cove (Tronic of EfFeCt)
for
ICTARI
Series 1, part 1, Getting started
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In the first part I am going to tackle very simple but very necessary
things like supervisor mode, exits, colours, move and movem
commands...
_____________________________________________
Section 1.1 - Supervisor mode using the -(sp)
ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿ
Here is the very standard routine to "get your machine into supervisor
mode".
You are able to add things before the following routine to calculate
how much memory you have, etc, but I will not go into this. Also, some
routines do not need supervisor mode to run, but more about his later.
Here is how to enter supervisor mode:
--------------------------------------------------------------------
clr.l -(sp) ... line 1.1
move.w #$20,-(sp) ... line 1.2
trap #1 ... line 1.3
addq.l #6,sp ... line 1.4
--------------------------------------------------------------------
At this point (after line 4) you are able to save the value in your
stack so you can restore the value when you end your program but more
about that later.
You are now in supervisor mode!! You can now play around with the
colours, hertz, CPU (!) etc....
The following piece of code is how you end your programs, i.e. to end
supervisor mode and return control to the C(entral) P(rocessing)
U(nit).
----------------------------------------------------------------------
clr.l -(sp) ... line 3.1
trap #1 ... line 3.2
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This will return the control to the CPU and effectively end your
program!!!
So if you were to add the previous bits of code together, all that
would happen is, you would simply return to Devpac and nothing would
change or have happened!!!
It is surprising that most people, who use 68000 to do intros and
people who want to figure out 68000 do not know about this!!
___________________________________________________________
Section 1.2 - Colour, using the move.w and movem.l commands
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Right, first off I will list the pitiful 16 colour registers:-
$ffff8240 - The background colour
$ffff8242 - Colour 2
$ffff8244 - Colour 3
$ffff8246 - Colour 4
$ffff8248 - Colour 5
$ffff824a - Colour 6
$ffff824c - Colour 7
$ffff824e - Colour 8
$ffff8250 - Colour 9
$ffff8252 - Colour 10
$ffff8254 - Colour 11
$ffff8256 - Colour 12
$ffff8258 - Colour 13
$ffff825a - Colour 14
$ffff825c - Colour 15
$ffff825e - Background colour
Now I will list the simple colour palettes:-
$000 - Black
$001 - Dark Blue
$007 - Light Blue
$010 - Dark Green
$070 - Light Green
$110 - Dark Yellow
$770 - Light Yellow
$100 - Dark Red
$700 - Light Red
$101 - Dark Purple
$707 - Light Purple
$011 - Dark Cyan
$077 - Light Cyan
$111 - Grey ... Scale 1
$222 - Grey ... Scale 2
$333 - Grey ... Scale 3
$444 - Grey ... Scale 4
$555 - Grey ... Scale 5
$666 - Grey ... Scale 6
$777 - White
$704 - Magenta (in red/purple scale)
So, if you wanted to change the background colour to red, then you
would write the following line:-
move.w $700,$ffff8240.w
|||||| |||| |||||||||||
111111 2222 33333333333
Sequence one is the move command that will effectively move what is
defined in sequence two, and implement it into sequence three!! Yes??
So, sequence one is the move command, sequence two is the data you are
moving to sequence three, and sequence three is the background colour
register,or what you want to be changed by what is in sequence two!!!
Easy really!!!
So, you can change sequence two, for different colours and you can
change sequence three for other colour registers!! You can also move
sequence two into a data bank, so you can use it, for restoring, or
whatever, later on...
=============------------------------------
program start - for example SUPERVISOR MODE
=============------------------------------
move.w $700,red_colour_bank
=======
program
=======
move.w red_colour_bank,$ffff8240.w
===========--------------------------------------
program end - for example clr.l -(sp) ... trap #1
===========--------------------------------------
red_colour_bank dc.w 0
Now it gets a little more complicated. You are moving $700 into the
data bank called red_colour_bank, which incidentally you can call
whatever you wanted, but you MUST define what kind of store
red_colour_bank is!!!! For example :-
you are using a "move.w" command, so the bank MUST be defined as a
"dc.w"....
You get different kinds of stores, they are "dc.w", "dc.b" and
"dc.l", plus the "dc.b" and others which I will go into later!! You
MUST NOT mix and match the ".w" with the ".l" with the ".b"!!! If
you are using the "move.b" command to move data into a bank, then you
MUST have a "dc.b" store!!!!!!!!!!
The same when you are using the banks, if you have used a "dc.b"
store, then you must using the "move.b" (or whatever)to use what is
in the store correctly!
I hope I have explained this so it is easy to understand, it is a
very easy concept which MUST be obeyed!!
So, if you have understood this, then you can see what it can be used
for in say an intro...you can save the contents of the colour
registers into sixteen banks and then restore then, by moving the
contents of each store into their respective colour registers......oh
god, this is getting complicated!!!!!!!!
There is a far easier way of does this, though........you can use a
"movem.l" command!!! For example:-
If you wanted to store and restore the ST palette, you would do it
like this:-
=============------------------------------
program start - for example SUPERVISOR MODE
=============------------------------------
movem.l $ffff8240,d0-d7
movem.l d0-d7,sts_colour_bank
===========--------------------------------------
program end - for example clr.l -(sp) ... trap #1
===========--------------------------------------
sts_colour_bank dc.l 16
Now, you should be able to see you this works instantly........it
simple moves the sixteen colour datas into the register d0-d7 and then
moves the contents of d0-d7 into the bank, which can hold up to
sixteen different data bits, sts_colour_bank. You can then restore
the palette with the following routine:-
=============------------------------------
program start - for example SUPERVISOR MODE
=============------------------------------
movem.l sts_colour_bank,d0-d7
movem.l d0-d7,$ffff8240
===========--------------------------------------
program end - for example clr.l -(sp) ... trap #1
===========--------------------------------------
sts_colour_bank dc.l 16
See, it is very easy!! You can then use this routine to store any
value you want, for example, the vbl values and mfg values......no I
will not explain these, yet....I do not fully understand them
myself!!!
Anyway, I think that is enough for this part, as there is quite a lot
here to get to grips with!! You must try these routines out for
yourself and mess around with them to see what you can do!! Have fun
and good luck!
It is a very good idea to get a reset resident version of Devpac
too!!!!!!
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Tronic of Effect, aka John Cove, [C]opyright 1995 ... started: 04-11-
1995 finished: 05-11-1995
"I reserve the right to publish these tutorial series
wherever I choose... Only, with express written
confirmation, is this to be published by anyone
other than myself. These series were written for
ST WORLD, but if I feel that the series is not being
taken advantage of in the way that most ST USERS are
able to read the series, then I will publish the
series in my own, and other peoples, disk magazines
and products."
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