The Atari MC68000 Tutorials

[membot]

Right, so, my formatting was the culprit ... i'll be tabbing around quite a bit more now

[spiny]

Right, so, my formatting was the culprit ... i'll be tabbing around quite a bit more now

yeah, devpac is quite funny about having tabs everywhere

[membot]

Glad I sorted that out quickly, Spiny. That's one of those things that can drive one mad by sheer frustration of unknown simplicity

[Nyh]

Right, so, my formatting was the culprit ... i'll be tabbing around quite a bit more now

The normal way is to use a ';' for comments. AFAIK is Devpac to only assembler that also uses tabs. When you are planning to share code with non Devpac users please get used to place a ';' for your comments.

Code: Select all

     clr.l   -(a7)        ; clear stack
     move.w  #32,-(a7)    ; prepare for super mode
     trap    #1           ; call gemdos
     addq.l  #6,a7        ; clear up stack
     move.l  d0,old_stack ; backup old stack pointer
     move.w  #$700,$ffff8240 ; red background color
     move.l  old_stack,-(a7) ; restore old stack pointer
     move.w  #32,-(a7)    ; back to user mode
     trap    #1           ; call gemdos
     addq.l  #6,a7        ; clear stack
     clr.l   -(a7)        ; clean exit
     trap    #1           ; call gemdos
old_stack:
     dc.l 0

Hans Wessels

[rocket-dog]

I am going to be lazy so apologies in advance. I know there is some discussion here about the virtues of the various marks of DevPac. Not qualified to know one from another. But if I download DevPac 2 can I still use this tutorial? Or is it only applicable to DevPac 3?

(PS: If anybody knows of a DevPac 3 download as separate files not an image I would be grateful.)

[spiny]

devpac 3 here:

http://dhs.nu/files.php?t=single&ID=5

[rocket-dog]

devpac 3 here:

http://dhs.nu/files.php?t=single&ID=5

Thank you. I have looked and looked and looked and looked and looked and looked and looked and looked and looked but to no avail.

I think I will just go with DevPac 3. You guys can carry discussing the merits of 3 vs 2 and 2 vs 3. I wouldn't understand what was being said anyway.

[spiny]

devpac 3 here:

http://dhs.nu/files.php?t=single&ID=5

Thank you. I have looked and looked and looked and looked and looked and looked and looked and looked and looked but to no avail.

I think I will just go with DevPac 3. You guys can carry discussing the merits of 3 vs 2 and 2 vs 3. I wouldn't understand what was being said anyway.

I used v3 when I went through the tutorials and everything worked as it should

[rocket-dog]

It is a sign that I haven't been here much over the last 9 months or so that you have forgotten my infinite capacity to cock up the simplest of tasks and miss the blatantly obvious. All of which I achieve without the aid of a safety and with no skill whatsoever!

[xdy0d3x]

a great read.Thanks!

[qwe]

Hello everybody,

I thank the author of this tutorial for the excellent work.
I'm learning 68000 on Atari ST just for fun; this tutorial is essential for beginners and is better than most books.
I wish I had the book "Atari ST internals" but on the net I could not find a copy in electronic format.
Are there other books that explain how to use the various trap functions?

Thanks very much for you help.

[MiggyMog]

http://dev-docs.atariforge.org/

[zonky900]

Just wanted to also say thanks for these documents, I used to code 68k for old Macs really long ago but am excited to start working on the ST too

[viking272]

Just wanted to also say thanks for these documents, I used to code 68k for old Macs really long ago but am excited to start working on the ST too

Yes they are good!
These tutorials are in part a homage to Andreas Wahlin (aka Perihelion) who was sadly murdered in 2007.

http://www.atarilegend.com/contact/andreas.php

The comments at the bottom of the above webpage are very touching.

[Kriegor]

Just stumbled upon these tutorials after about a year of not giving my ST some data love, and wow! Thought I'd never be interested in programming (never been) but ASM on the ST is really fun, in a strange learning-how-computers-really-work way And of course, the lot of it owes to the great way that it is written, learn-by-doing pedagogic and relaxed with a lot of humorous and casual reliefs. Really sad to hear about Perihelions death... Or rather, to hear that it was actually the guy who wrote this who was killed for his laptop that time in Bergsjön back in 2007 (I'm from the same town so i read those news).

About the tutorials though, which I've read the PDF version of to tutorial #5 now; Seems like there is a small error in the code which i managed to fix so that it works as intended (yay!). Either that, or I'm doing something wrong (but still getting the result right). Example code from the PDF:

Code: Select all

                        section data

old_palette         ds.l        8

old_resolution     dc.w        0

old_stack            dc.l        0


                        section dss

old_screen          dc.l        0

I first thought that that was intended, in order to give you a little excercise, but the text doesn't say so - in fact, that part of the code is there just to make it work and not a part of the tutorial really... except for us "curious types"

I first tried to run it but DevPac gave me an error at "section dss". Looking back some pages and changing it made it clear, it's "bss" and not "dss" (block storage segment) right? Seems to be a simple typo

Solved that problem, but it gave me another one at the next "old_screen" line ("BSS section cannot contain data"). Looking back again it was quite clear to me that the whole part of this code seems to be a bit wrong. "The DC area should be denoted by a “section data”, and the DS section should be denoted by a “section bss” (Block Storage Segment).". So, the old_palette which is a "define storage" is in the wrong section, and the same goes for the old_screen, a "define constant" which is placed in the storage section. At least that made sense to me, DevPac, and it assembled, executed and terminated back to the editor without any problems!

Code: Select all

                        section data

old_screen          dc.l        0

old_resolution     dc.w        0

old_stack            dc.l        0


                        section bss
old_palette         ds.l        8


This is the new part of the code after i edited it (sorry for the indent-errors). Am I on track here?

[Anima]

Am I on track here?

Hello Kriegor,

yes.

You have learned the hard way why it is sometimes really awkward to use assembly code between different assemblers. However, albeit some assemblers allow to have "ds.x" within the data section it seems that "section dss" is indeed a typo.

Some additional notes:

As any of these "memory variables" will be defined at the initialisation routine all of them can be moved to the BSS. So it would look like this:

Code: Select all

.data
.bss
old_palette:        ds.w 16
old_resolution:     ds.w 1
old_stack:          ds.l 1
old_screen:         ds.l 1

Advantage: the memory space used to store the values will not add up to the program size.

You may ask why I have chosen "ds.w 16" over "ds.l 8". Well, you should use the original size of the data even if it is the same result but later on it's easier to understand and easier to change the code.

Another example is declaring a two dimensional array:

Code: Select all

.bss
.align 4
screen_buffer:    ds.w 320*240

This example declares a true colour screen buffer for the Falcon030 which says: 320 pixels wide by 240 pixels height with a pixel size of 16 bits (one word). So if you want to change your resolution you can do it by changing the values.

It's better than having this:

Code: Select all

.bss
.align 4
screen_buffer:    ds.l 38400

Cheers
Sascha

[Kriegor]

Am I on track here?

Hello Kriegor,

yes.

You have learned the hard way why it is sometimes really awkward to use assembly code between different assemblers. However, albeit some assemblers allow to have "ds.x" within the data section it seems that "section dss" is indeed a typo.

Some additional notes:

As any of these "memory variables" will be defined at the initialisation routine all of them can be moved to the BSS. So it would look like this:

Code: Select all

.data
.bss
old_palette:        ds.w 16
old_resolution:     ds.w 1
old_stack:          ds.l 1
old_screen:         ds.l 1

Advantage: the memory space used to store the values will not add up to the program size.

You may ask why I have chosen "ds.w 16" over "ds.l 8". Well, you should use the original size of the data even if it is the same result but later on it's easier to understand and easier to change the code.

Another example is declaring a two dimensional array:

Code: Select all

.bss
.align 4
screen_buffer:    ds.w 320*240

This example declares a true colour screen buffer for the Falcon030 which says: 320 pixels wide by 240 pixels height with a pixel size of 16 bits (one word). So if you want to change your resolution you can do it by changing the values.

It's better than having this:

Code: Select all

.bss
.align 4
screen_buffer:    ds.l 38400

Cheers
Sascha

Hi! Thanks for your input!

Indeed, making the palette storage 16 words instead of 8 longwords naturally makes it more intuitive, did that to my code and it still works like a charm! I also tried to make the dc.N:s ds.N:s instead, and indeed as you say, it made the .PRG 10 bytes smaller compared to when using the dc:s. Kind of makes sense as 2*4 (longwords) and 1*2 (words) = 10 bytes! Even though i haven't really gotten to that part of the tutorials it's good to have it in mind for the future!

I personally like those little errors (i think there are a few more, no biggies though) as it makes you need to dig deeper into the code than just copy it all, nice for repetition. Anyway i guess i should stop hijacking this thread and get on with the coding I'll get back in a more relevant thread if i get stuck at something and can't find any info on it. Let's just conclude that the tutorials have some small "accidential challenges"/errors/typos, but nothing you shouldn't be able to handle at that point anyway. Thanks for the hint on memory-saving!

[Silly_Pony]

Great tutorials but packaged stupid, Single files buried five hundred feet deep

alltuts.zip/tut01.zip/tut01/tut01.pdf

Seems overkill?!

[LynXX]

Hi there,

I really enjoyed these tutorials, but I was a bit frustrated by the PDF format and the inability to fix minor typos and stuff, so I spent some time converting them to AsciiDoc, and rendering them in HTML.

The result is here: https://nguillaumin.github.io/perihelio ... tutorials/ , and the sources are on GitHub: https://github.com/nguillaumin/periheli ... -tutorials

I haven't changed much, it's mostly the original texts with a few fixes. I reformatted the source code to (hopefully) make them a bit more readable. I left all the credits where they were due, the idea was not to steal or take over but really to make them easier to share and contribute to.

I also setup a cross-assembly setup with VASM which can be used as a base for larger projects (See src/Makefile).

I hope that will make them a bit more accessible (especially when reading on mobile devices), and will allow more contributions via GitHub to fix issues or typos, and who knows maybe write additional tutorials?

Comments welcome, also feel free to raise issues on GitHub or submit pull requests!

edit: If people find this valuable, perhaps a mod could edit the first post of the thread to add a link to this HTML version?

[mikro]

Man, this looks really awesome! Personally I came to the Perihelion tutorials way too late (when I already knew about m68k/TOS).

I'd advise to remove this line though:

He welcomes any and all feedback at <andreaswahlin@bredband.net>.

Unfortunately he does not, he was killed about 7 years ago, you can find info here on AF, too: http://atari-forum.com/viewtopic.php?t=11317. :-(

[LynXX]

Yeah I new about this sad fact, but I was a bit reluctant to modify the original text too much... Perhaps it makes sense though, let's see what other people think?

[TheNameOfTheGame]

Yeah I new about this sad fact, but I was a bit reluctant to modify the original text too much... Perhaps it makes sense though, let's see what other people think?

I would think it's appropriate to remove that line or perhaps replace it with some sort of "in memory of" line.

[LynXX]

Small update on this, the listings now have syntax highlighting. It's minor, but that make them a bit more readable.

syntax.png

It took me a while get all the pieces together, I had to start by contributing the m68k syntax to one of the syntax highlighter used by AsciiDoctor!

https://nguillaumin.github.io/perihelio ... tutorials/

[YQN]

Small update on this, the listings now have syntax highlighting. It's minor, but that make them a bit more readable.

syntax.png

It took me a while get all the pieces together, I had to start by contributing the m68k syntax to one of the syntax highlighter used by AsciiDoctor!

https://nguillaumin.github.io/perihelio ... tutorials/

Love this html version, merci !

[Cyprian]

true, really great tutorial
thanks

one remark, would be cool to have a screenshot,to show how particular fx looks like. e.g. "Of Lighting A Candle (And Casting A Shadow)"