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Home > Atari Memories > #Assembly > Atari 2600 Programming for Newbies

Atari 2600 Programming for Newbies

Session 8: Our First Kernel

By Andrew Davie (adapted by Duane Alan Hahn, a.k.a. Random Terrain)

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Page Table of Contents

Original Session

We're going to jump right in, now that we know what a kernel needs to do. Seen below, and in the attached file, is the source code for a working '2600 kernel. It displays the image you see here. Not bad for just a few lines of code. Over the next few sessions we'll learn how to modify this code, and assemble itand, of course, what all those strange words mean.

 

For now, have a look at the structure of the code and note how closely it relates to the structure of the TV frame diagram in the earlier sessions:

Don't expect to understand everythingwe'll walk through every line soon. For now, all you need to know is that the "sta WSYNC" is where the 6502 is telling the TIA to halt the 6502 until the start of the next horizontal blank period (which is at the start of the next scanline, at TIA color clock 0). So each of those lines is where one complete scanline has been sent to the TV by the TIA. Have a close look at those lines, and see how there are 3, followed by 37 (vertical blank period), followed by 192 (picture) followed by 30 (overscan)and how this exactly matches our TV frame diagram, above.

 

Yes, this is a complete kernel. It's not that difficult!

 

 

 

 

 

Source Code


            processor 6502

            include "vcs.h"

            include "macro.h"



            SEG

            ORG $F000



Reset

StartOfFrame



   ; Start of vertical blank processing



            lda #0

            sta VBLANK



            lda #2

            sta VSYNC

            

               ; 3 scanlines of VSYNCH signal...



                sta WSYNC

                sta WSYNC

                sta WSYNC



            lda #0

            sta VSYNC           



               ; 37 scanlines of vertical blank...



                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

            





               ; 192 scanlines of picture...

 

                ldx #0

                REPEAT 192; scanlines



                    inx

                    stx COLUBK

                    sta WSYNC



                REPEND



 

            lda #%01000010

            sta VBLANK                     ; end of screen - enter blanking



               ; 30 scanlines of overscan...



                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC

                sta WSYNC



            jmp StartOfFrame





            ORG $FFFA



            .word Reset          ; NMI

            .word Reset          ; RESET

            .word Reset          ; IRQ



    	END

I tried to make the code sample above as understandable as possible. It is certainly not the most efficient codefor it uses too many bytes of ROM to achieve its effect. But we're learning, and what's important right now is understanding how things work.

 

 

Here's a screenshot:

Here's the .bin file to use with an emulator:

kernel_01.bin

 

 

 

 

 

Summary

Next session we'll have a look at how to actually assemble this code using DASM, and how to make modifications so you can play with it and test it on the emulator to see what effect your changes have.

 

 

 

Other Assembly Language Tutorials

Be sure to check out the other assembly language tutorials and the general programming pages on this web site.

 

Amazon Stuff

 

< Previous Session

 

 

Next Session >

 

 

 

 

Session Links

Session 1: Start Here

Session 2: Television Display Basics

Sessions 3 & 6: The TIA and the 6502

Session 4: The TIA

Session 5: Memory Architecture

Session 7: The TV and our Kernel

Session 8: Our First Kernel

Session 9: 6502 and DASM - Assembling the Basics

Session 10: Orgasm

Session 11: Colorful Colors

Session 12: Initialization

Session 13: Playfield Basics

Session 14: Playfield Weirdness

Session 15: Playfield Continued

Session 16: Letting the Assembler do the Work

Sessions 17 & 18: Asymmetrical Playfields (Parts 1 & 2)

Session 19: Addressing Modes

Session 20: Asymmetrical Playfields (Part 3)

Session 21: Sprites

Session 22: Sprites, Horizontal Positioning (Part 1)

Session 23: Moving Sprites Vertically

Session 24: Some Nice Code

Session 25: Advanced Timeslicing

 

 

 

 

Useful Links

Easy 6502 by Nick Morgan

How to get started writing 6502 assembly language. Includes a JavaScript 6502 assembler and simulator.

 

 

Atari Roots by Mark Andrews (Online Book)

This book was written in English, not computerese. It's written for Atari users, not for professional programmers (though they might find it useful).

 

 

Machine Language For Beginners by Richard Mansfield (Online Book)

This book only assumes a working knowledge of BASIC. It was designed to speak directly to the amateur programmer, the part-time computerist. It should help you make the transition from BASIC to machine language with relative ease.

 

 

The Second Book Of Machine Language by Richard Mansfield (Online Book)

This book shows how to put together a large machine language program. All of the fundamentals were covered in Machine Language for Beginners. What remains is to put the rules to use by constructing a working program, to take the theory into the field and show how machine language is done.

 

 

6502 Instruction Set with Examples

A useful page from Assembly Language Programming for the Atari Computers.

 

 

6502.org

Continually strives to remain the largest and most complete source for 6502-related information in the world.

 

 

Guide to 6502 Assembly Language Programming by Andrew Jacobs

Below are direct links to the most important pages.

 

 

Stella Programmer's Guide

HTMLified version.

 

 

Nick Bensema's Guide to Cycle Counting on the Atari 2600

Cycle counting is an important aspect of Atari 2600 programming. It makes possible the positioning of sprites, the drawing of six-digit scores, non-mirrored playfield graphics and many other cool TIA tricks that keep every game from looking like Combat.

 

 

How to Draw A Playfield by Nick Bensema

Atari 2600 programming is different from any other kind of programming in many ways. Just one of these ways is the flow of the program.

 

 

Cart Sizes and Bankswitching Methods by Kevin Horton

The "bankswitching bible." Also check out the Atari 2600 Fun Facts and Information Guide and this post about bankswitching by SeaGtGruff at AtariAge.

 

 

Atari 2600 Specifications

Atari 2600 programming specs (HTML version).

 

 

Atari 2600 Programming Page (AtariAge)

Links to useful information, tools, source code, and documentation.

 

 

MiniDig

Atari 2600 programming site based on Garon's "The Dig," which is now dead.

 

 

TIA Color Charts and Tools

Includes interactive color charts, an NTSC/PAL color conversion tool, and Atari 2600 color compatibility tools that can help you quickly find colors that go great together.

 

 

The Atari 2600 Music and Sound Page

Adapted information and charts related to Atari 2600 music and sound.

 

 

Game Standards and Procedures

A guide and a check list for finished carts.

 

 

Stella

A multi-platform Atari 2600 VCS emulator. It has a built-in debugger to help you with your works in progress or you can use it to study classic games.

 

 

JAVATARI

A very good emulator that can also be embedded on your own web site so people can play the games you make online. It's much better than JStella.

 

 

batari Basic Commands

If assembly language seems a little too hard, don't worry. You can always try to make Atari 2600 games the faster, easier way with batari Basic.

 

 

Atari 2600 BASIC

If assembly language is too hard for you, try batari Basic. It's a BASIC-like language for creating Atari 2600 games. It's the faster, easier way to make Atari 2600 games.

Try batari Basic

Back to Top

 

 

In Case You Didn’t Know

 

B Vitamins = Good

Some people appear to have a mental illness because they have a vitamin B deficiency. For example, the wife of a guy I used to chat with online had severe mood swings which seemed to be caused by food allergies or intolerances. She would became irrational, obnoxious, throw tantrums, and generally act like she had a mental illness. The horrid behavior stopped after she started taking a vitamin B complex. I’ve been taking #ad Jarrow B-Right for many years. It makes me much easier to live with.

 

 

Soy = Bad

Unfermented soy is bad! “When she stopped eating soy, the mental problems went away.” Fermented soy doesn’t bother me, but the various versions of unfermented soy (soy flour, soybean oil, and so on) that are used in all kinds of products these days causes a negative mental health reaction in me that a vitamin B complex can’t tame. The sinister encroachment of soy has made the careful reading of ingredients a necessity.

 

 

Wheat = Bad

If you are overweight, have type II diabetes, or are worried about the condition of your heart, check out the videos by William Davis and Ivor Cummins. It seems that most people should avoid wheat, not just those who have a wheat allergy or celiac disease. Check out these books: #ad Undoctored, #ad Wheat Belly, and #ad Eat Rich, Live Long.

 

 

Negative Ions = Good

Negative ions are good for us. You might want to avoid positive ion generators and ozone generators. Whenever I need a new air cleaner (with negative ion generator), I buy it from surroundair.com. A plain old air cleaner is better than nothing, but one that produces negative ions makes the air in a room fresher and easier for me to breathe. It also helps to brighten my mood.

 

 

Litterbugs = Bad

Never litter. Toss it in the trash or take it home. Do not throw it on the ground. Also remember that good people clean up after themselves at home, out in public, at a campsite and so on. Leave it better than you found it.

 

 

Climate Change Cash Grab = Bad

Seems like more people than ever finally care about water, land, and air pollution, but the climate change cash grab scam is designed to put more of your money into the bank accounts of greedy politicians. Those power-hungry schemers try to trick us with bad data and lies about overpopulation while pretending to be caring do-gooders. Trying to eliminate pollution is a good thing, but the carbon footprint of the average law-abiding human right now is actually making the planet greener instead of killing it.

 

Watch these two YouTube videos for more information:

CO2 is Greening The Earth

The Climate Agenda

 

 

Hydrofracking = Bad

Hydrofracking is bad for you, your family, your friends, and the environment.

 

 

Hydroxychloroquine = Good

Although some people with certain conditions may not be able to take it, hydroxychloroquine is a cheap drug that has been prescribed by doctors since the 1950s and it seems to be helping many people who have COVID-19 when administered early enough. (Hydroxychloroquine is also supposedly safe and tolerable as an anti-cancer therapy.) Seems like most news sources are going out of their way to make it sound like hydroxychloroquine is the most dangerous drug in the world, but they also make it sound like it’s the greatest drug in the world for lupus and rheumatoid arthritis patients. They basically say that using hydroxychloroquine for COVID-19 patients would be taking that great and wonderful drug away from the other patients who need it. So which is it? Is hydroxychloroquine deadly or divine?

 

If you believe that a couple of Trump supporters took the medicine hydroxychloroquine and it’s President Trumps fault that the husband died, you’ve been duped. Watch this video. The wife was a prolific Democratic donor, it seems she hated her husband, she used fish tank cleaner (not the medicine hydroxychloroquine), and now she is the subject of a homicide investigation.

 

Some people claim that the reason so many news sources want to keep doctors from using hydroxychloroquine for COVID-19 is that they are desperate to keep everyone afraid to leave their homes since mail-in voting will make voter fraud much easier (the only way they could beat Trump). Others claim that the rabid anti-hydroxychloroquine campaign was to make way for the expensive new drug called remdesivir. Drug companies can’t make much money with old generic drugs, so new drugs must be pushed. Both claims could be true since remdesivir supposedly isn’t as good as hydroxychloroquine.

 

According to Dr. Shiva Ayyadurai, hydroxychloroquine does four things: (1) stops viral entry, (2) stops viral RNA replication, (3) stops viral particle assembly, and (4) stops cytokine storm. Remdesivir only stops viral RNA replication. Did you get that? Hydroxychloroquine does four things and remdesivir only does one. The doctor also said that nearly 70 percent of the people who took remdesivir had some type of adverse effect. If all of that is true and the more anemic medicine ends up being used by most doctors thanks to the smear campaign against hydroxychloroquine, the average American will beg to vote from home.

 

In case you didn’t know, Patrick Howley reported that one of the authors of the ‘study’ saying that hydroxychloroquine doesn’t work at VA hospitals got a research grant from Gilead (the company that makes remdesivir). Does that seem a little fishy to you?

 

Bryan Fischer said in an article that Dr. Fauci has known since 2005 that chloroquine is an effective inhibitor of coronaviruses. You might also want to check out the following three links:

The REAL Truth about Dr. Fauci, Remdesivir and Hydroxychloroquine!

Chloroquine Is a Potent Inhibitor of SARS Coronavirus Infection and Spread (2005)

Sequential CQ / HCQ Research Papers and Reports

 

“The Disruptive Physician” had this to say at Twitter: “Meanwhile, regular doctors like me are using HCQ + Azithromycin and Zinc to good effect. One nursing home in NE Ohio had 30 cases - started everyone on HCQ, no deaths. Quick recovery. Why would the MSM hide this? Why would twitter block people who question the WHO?” You might also want to check out Dr. Stephen Smith, Dr. Ramin Oskoui and Dr. Yvette Lozano.

 

In case you’re interested, here are a few COVID-19 patients who appear to claim that hydroxychloroquine saved their lives: elderly couple Louis Amen and Dolores Amen, Daniel Dae Kim, Rio Giardinieri, John McConnell, Margaret Novins, Jim Santilli, Billy Saracino, and Karen Whitsett (Democratic member of the Michigan House of Representatives).

Disclaimer

View this page and any external web sites at your own risk. I am not responsible for any possible spiritual, emotional, physical, financial or any other damage to you, your friends, family, ancestors, or descendants in the past, present, or future, living or dead, in this dimension or any other.

 

Use any example programs at your own risk. I am not responsible if they blow up your computer or melt your Atari 2600. Use assembly language at your own risk. I am not responsible if assembly language makes you cry or gives you brain damage.

 

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