Similarities to Intellivision and Atari 2600 assembly

[doctorclu]

So here is a deep question, has anyone tried to port an Atari 2600 game to the Intellivision?

 

I'm curious, before re-inventing the wheel, if certain assembly functions in Atari 2600 and their counterparts were found for the Intellivision and visa versa?

 

Have tools been made to help in the conversion process?

 

Thanks!

[+DZ-Jay]

First off the bat: they are two different CPU architectures with very little in common between them. Likewise for the graphics and video processing of both the Atari TIA and the Intellivision STIC.

 

Although I'm sure that code could be converted between them, it almost seems to me like re-implementing an Atari 2600 game in IntyBASIC from scratch would be a heck of a lot easier.

 

Is there a particular game you had in mind? Perhaps we can offer some insight on how to go about the conversion process for a specific title.

 

-dZ.

[intvnut]

The Atari 2600 and Intellivision programming models are rather different.

 

In particular, a big part of programming an Atari 2600 game involves writing a graphics kernel to literally "chase the beam" down the screen to generate the play field. None of that logic directly translates to the Intellivision. The Intellivision uses the STIC to generate graphics from its character-tile oriented display. Mapping one to the other is non-trivial, and really requires thinking about the hardware and how best to make it achieve whatever effect(s) you're going for. The STIC doesn't let you program its registers during active display, and the updates you can do to BACKTAB are limited to staying ahead of the row fetches that happen 12 times per frame.

 

Beyond that is the game logic, which is proportionally a much smaller piece of the equation. Interpreting the 6502 code might help you understand the vagaries of a particular game's implementation, but I don't think it lends itself to a direct translation.

 

As dZ says, you're better off starting from a game concept and reimplementing than trying to convert the 6502 code for an Atari 2600 game to Intellivision. It's too big of an impedance mismatch.

[carlsson]

If you're looking to translate 6502 code to Intellivision, I would imagine something like VIC-20 to be much closer than the Atari 2600 is, but yes generally you are much better off starting from a higher level language.

[doctorclu]

If you're looking to translate 6502 code to Intellivision, I would imagine something like VIC-20 to be much closer than the Atari 2600 is, but yes generally you are much better off starting from a higher level language.

 

All good input and yes, and the input from Carlsson above answers my next question of which systems may be closer.

 

The game I wanted to try to port was Fast Eddie to the Intellivision (because that was the basis of all my Bubsy graphical hacks) So of that there were the versions of Fast Eddie for the Atari 2600, Atari Computer, Commodore 64, and Vic-20. If the Vic-20 is the closest jumping off point, I might take a look at that.

[carlsson]

Haha, I was about to ask that question but withheld it!

 

While I know people in the Atari 8-bit computer scene successfully have ported games for both the C64 (equally 6502 based) and ZX Spectrum (Z80 based) to the Atari computers, it involves a lot of hand work. I know the very rare Keyboard Component for the Intellivision is 6502 based, but the similarities probably end there.

 

Actually you'll be much better off writing your own Fast Eddie clone on the Intellivision (or find a similar platform based game if one exists), or even write your own inofficial Bubsy game from scratch on the Intellivision.

[+DZ-Jay]

By the way, I encourage you to check out IntyBASIC, and in particular the IntyBASIC SDK. It is a very powerful yet simple programming language which gives you very close to the raw power and speed of Assembly Language with the simplicity and versatility of BASIC.

 

It is a compiled language built with modern techniques so none of the performance and storage issues of the old BASIC from the micro-computer days apply. (Plus, I hear from many programmers coming from other platforms that it is a really fun language to use.)

 

You may find that implementing the game from scratch for the Intellivision using IntyBASIC may not be such a daunting task.

 

The challenge is, like intvnut said, getting acquainted with the Intellivsion programming model and it's peculiarities. But for that, we're here to help.

 

dZ.

[carlsson]

Order Oscar's new book on Intellivision programming, it includes an entire chapter on making a platform game (Monkey Moon) from which you would be able to reuse a couple of mechanisms for a head start.