https://github.com/barrettotte/game-2600
A screw around project in 6502 assembly for the Atari 2600 (VCS)
https://github.com/barrettotte/game-2600
assembly-6502 atari-2600
Last synced: about 1 year ago
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A screw around project in 6502 assembly for the Atari 2600 (VCS)
- Host: GitHub
- URL: https://github.com/barrettotte/game-2600
- Owner: barrettotte
- Created: 2020-01-09T03:05:44.000Z (over 6 years ago)
- Default Branch: master
- Last Pushed: 2020-06-04T01:21:27.000Z (about 6 years ago)
- Last Synced: 2025-02-03T13:13:20.231Z (over 1 year ago)
- Topics: assembly-6502, atari-2600
- Language: Assembly
- Homepage:
- Size: 74.2 KB
- Stars: 1
- Watchers: 3
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
# Game-2600
Some fun messing around with 6502 assembly on the Atari 2600 (VCS).
## Game
This isn't quite a game; its more of a screw around project I kicked around.
At this point its only a skeleton and has the following:
* Scoreboard and timer BCD display
* Player movement with joysticks
* Graphics and color binary loading
* Reset button
* A bit of black and white TV support
* Random numbers via Linear Feedback Shift Register (LFSR)
I really wanted to do more with this.
But, truthfully I just don't feel like working on it anymore.
Its time for this to go on the shelf.
## Screenshot
Yeah...this is all I have after ~2 weeks of messing around. This stuff is difficult for me.
## Stella Emulator Controls
* Arrow keys - joystick
* Spacebar - fire
* F2 - reset
* F3 - color TV
* F4 - black and white TV
* PAUSE - pause emulator
## Unimplemented Ideas
* Full black and white TV support
* Player and enemy projectiles
* Basic pathfinding for Enemy
* Difficulty switches increase enemy speed
* Random generated playfield obstacles
## Notes
#### Memory Map
```
+---------------------------+
| TIA Registers | $00-$7F
+---------------------------+
| PIA RAM | $80-$FF
+---------------------------+
| ??? |
+---------------------------+
| PIA Ports and Timer | $280-$297
+---------------------------+
| ??? |
+---------------------------+
| Cartridge ROM | $F000-$FFFF
+---------------------------+
```
#### NTSC Video Frame
```
+-------------------------------------------------+ <-----+
| Vertical Sync | 3 lines |
| | |
+-------------------------------------------------+ |
| Vertical Blank | 37 lines |
| | |
+--------------------+----------------------------+ +-- 262 lines
| Horiz. | Visible | |
| Blank | Frame | 192 lines |
| | <-- 160 color clocks --> | |
+--------------------+----------------------------+ |
| Overscan | 30 lines |
| | |
+-------------------------------------------------+ <-----+
|-------------- 228 color clocks ----------------|
|--------------- 76 CPU cycles -----------------|
```
## References
**Main reference**: https://atariage.com/forums/profile/3056-spiceware/ . This guy is absolutely incredible with 6502 asm.
* 6502 instruction set with cycle counts - https://www.masswerk.at/6502/6502_instruction_set.html
* Atari 2600 killer hacks - https://atariage.com/forums/topic/71120-6502-killer-hacks/page/3/?tab=comments#comment-1071314
* ```.byte $2C``` - "skip 2 bytes" pseudo-instruction (ABS BIT)
* Counting cycles on Atari 2600 - https://www.randomterrain.com/atari-2600-memories-guide-to-cycle-counting.html
* DASM Macro Assembler - https://github.com/munsie/dasm
* Introduction to Atari2600 - https://www.randomterrain.com/
* Sprite ASM Generator - https://alienbill.com/2600/playerpalnext.html
* Stella Emulator - https://stella-emu.github.io/
* Unofficial 6502 opcodes - https://wiki.nesdev.com/w/index.php/Programming_with_unofficial_opcodes
* ```dcp $0F``` - decrement at memory address and compare with accumulator