Getting started
Assembly language, in Devpac, Tutorial by John Cove (Tronic of EfFeCt) for ICTARI Series 1, part 1, Getting started ---------------------------------------------------------------------- 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 ---------------------------------------------------------------------- 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 ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿ 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!!!!!! ---------------------------------------------------------------------- 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."
Back to ASM_Tutorial