A snake game clone for Commodore home computers
You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
 
 
 
giomba 9c902abb59 intro/demo: show PETSCII brand name + forbid intro skip 1 year ago
dist disk and tape loader 2 years ago
liblzg@182b56cb36 compression routine for cartridge version, temporarily deprecates tape version 2 years ago
res.org refactoring: wip: move code segments 1 year ago
scrot polishing 1 year ago
src intro/demo: show PETSCII brand name + forbid intro skip 1 year ago
util updated sid tune 2 years ago
.gitignore added distribution binary file .prg 3 years ago
.gitmodules compression routine for cartridge version, temporarily deprecates tape version 2 years ago
LICENSE.md updated LICENSE 2 years ago
Makefile polishing 1 year ago
README.md polishing 1 year ago

README.md

snake6502

Intro screenshot Gameplay screenshot

snake6502 is a snake-like game clone for Commodore home computers, written for fun because «I always wanted to code something for a computer of my retrocomputers collection – actually, this is the main reason I collect them: to write programs».

Current development status here.

Download

  • .d64 for floppy disks
  • .bin for 8KiB cartridges

Compile

You need the GNU compiler collection and the dasm macro assembler, then:

$ git submodule init
$ git submodule update
$ make

Interesting targets:

  • make bin/snake6502.bin produces .bin, ready to be burnt on an 8K EEPROM for making a cartridge
  • make bin/snake6502.d64 produces .d64, ready to be used for floppy disks

You can also define the following environment variables:

$ DEBUG=1 make build with debugging artifacts

Tape

Copy loader.prg and packlz from disk to tape. On a physical machine, you can use disk2tape.

Developer docs

Package

The whole program is assembled into a snake.pack binary blob with the following structure.

Absolute Offset Description
$1000 $0000 load address
$2800 $1800 entry point (start address)

Memory map

Address PRG Description
$0000 - $0001 no hardware
$0002 - $00FF no zero page pointers
$0100 - $01FF no stack page
$0200 - $03FF no operating system variables
$0400 - $07FF no video memory
$1000 - $1FFF yes SID tune, may overlap charset
$2000 - $23FF yes custom char, unused, allow SID overlap
$2400 - $27FF yes custom char (actual 0x80+)
$2800 - $xxxx yes Program segment (only needed part used)
$xxxx - $CCFF no free ram
$CD00 - $CFFF no data segment (not-initialized vars)
$D000 - $DFFF no I/O
$E000 - $FFFF no Kernal

Compression

snake.pack is compressed into snake.pack.lz using liblzg, to save space, mainly in order to fit the game in a *PROM. Decompression occurs with one of the following loaders.

Loader

Cartridge

cart.asm is located at $8000 (standard org address for C64 cartridges), and contains the decompression routine and the snake.pack.lz. It decompresses snake.pack.lz back to $1000, and jumps to its entry point at $2800.

Disk

loader.asm loads at $801, like any other BASIC automatic runner, and contains the decompression routine. snake.pack.lz is loaded at $8000 from disk drive, then decompressed back to $1000, and finally the loader jumps to the program entry point at $2800.

Miscellanea

Custom charset

Index Description
$00 - $7F unused (space for SID)
$80 - $9F A-Z (space first)
$A0 - $BF A-Z, reversed (space first)
$C0 - $CF hex digits
$D0 - $DF hex digits, reversed
$E0 - $EF game tiles
$F0 - $FF semigraphic tiles
Semigrahic Tiles
Char Output
$F0
$F1
$F2
$F3
$F4 -
$F5 ```
$F6
$F7
$F8
$F9
$FA
$FB
$FC
$FD