By Andrew Davie (adapted by Duane Alan Hahn, a.k.a. Random Terrain)
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Page Table of Contents
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 it—and, 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 everything—we'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!
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 code—for 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:
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: Atari 2600 Programming (#ad)
Amazon: 6502 Assembly Language Programming (#ad)
Atari 2600 Programming for Newbies (#ad)
Making Games for the Atari 2600 (#ad)
Session 2: Television Display Basics
Sessions 3 & 6: The TIA and the 6502
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 14: Playfield Weirdness
Session 15: Playfield Continued
Session 16: Letting the Assembler do the Work
Sessions 17 & 18: Asymmetrical Playfields (Parts 1 & 2)
Session 20: Asymmetrical Playfields (Part 3)
Session 22: Sprites, Horizontal Positioning (Part 1)
Session 22: Sprites, Horizontal Positioning (Part 2)
Session 23: Moving Sprites Vertically
Session 25: Advanced Timeslicing
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 6502 Instruction Set broken down into 6 groups.
Nice, simple instruction set in little boxes (not made out of ticky-tacky).
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.
An easy-to-read page from The Second Book Of Machine Language.
6502 Instruction Set with Examples
A useful page from Assembly Language Programming for the Atari Computers.
Continually strives to remain the largest and most complete source for 6502-related information in the world.
By John Pickens. Updated by Bruce Clark.
Guide to 6502 Assembly Language Programming by Andrew Jacobs
Below are direct links to the most important pages.
Goes over each of the internal registers and their use.
Gives a summary of whole instruction set.
Describes each of the 6502 memory addressing modes.
Describes the complete instruction set in detail.
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 programming specs (HTML version).
Atari 2600 Programming Page (AtariAge)
Links to useful information, tools, source code, and documentation.
Atari 2600 programming site based on Garon's "The Dig," which is now dead.
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.
A guide and a check list for finished carts.
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. Stella finally got Atari 2600 quality sound in December of 2018. Until version 6.0, the game sounds in Stella were mostly OK, but not great. Now it's almost impossible to tell the difference between the sound effects in Stella and a real Atari 2600.
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.
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.
Did you know that Trump's rushed experimental rona jab has less than one percent overall benefit? It also has many possible horrible side effects. Some brainwashed rona jab cultists claim that there are no victims of the jab, but person after person will post what the jab did to them, a friend, or a family member on web sites such as Facebook and Twitter and they'll be lucky if they don't get banned soon after. Posting the truth is “misinformation” don't you know. Awakened sheep might turn into lions, so powerful people will do just about anything to keep the sheep from waking up.
Check out these videos:
What is causing the mysterious self-assembling non-organic clots?
If You Got the COVID Shot and Aren't Injured, This May Be Why
Full Video of Tennessee House of Representatives Health Subcommittee Hearing Room 2 (The Doctors Start Talking at 33:28)
Take a look at my page called The H Word and Beyond. You might also want to look at my page called Zinc and Quercetin. My sister and I have been taking those two supplements since summer of 2020 in the hopes that they would scare away the flu and other viruses (or at least make them less severe).
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 Jarrow B-Right (#ad) for many years. It makes me much easier to live with.
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.
If you are overweight, have type II diabetes, or are worried about the condition of your heart, check out the videos by Ken D Berry, 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: Undoctored (#ad), Wheat Belly (#ad), and Eat Rich, Live Long (#ad).
Negative ions are good for us. You might want to avoid positive ion generators and ozone generators. 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.
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.
Eliminating farms and ranches, eating bugs, getting locked down in 15-minute cities, owning nothing, using digital currency (with expiration dates) that is tied to your social credit score, and paying higher taxes will not make things better and “save the Earth.” All that stuff is part of an agenda that has nothing to do with making the world a better place for the average person. It's all about control, depopulation, and making things better for the ultra-rich. They just want enough peasants left alive to keep things running smoothly.
Watch these two YouTube videos for more information:
Charlie Robinson had some good advice about waking up normies (see the link to the video below). He said instead of verbally unloading or being nasty or acting like a bully, ask the person a question. Being nice and asking a question will help the person actually think about the subject.
Charlie Robinson Talks About the Best Way to Wake Up Normies
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.