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A snake game clone for Commodore home computers
63 Commits 3 Branches 4 Tags 190 KiB
Assembly 95.6%
C++ 2.3%
Makefile 2.1%
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giomba c8199e7144 updated sid tune 
new sid tune is bigger than 4k, so charset had to be moved
now (part of) first half of the charset actually is used by the sid
and ignored by the VIC; chars had to be redefined
2021-04-12 23:28:34 +02:00
dist disk and tape loader 2021-04-12 22:00:04 +02:00
liblzg@182b56cb36 compression routine for cartridge version, temporarily deprecates tape version 2020-10-04 17:51:35 +02:00
res.org compression routine for cartridge version, temporarily deprecates tape version 2020-10-04 17:51:35 +02:00
scrot added cute screenshot 2020-04-23 12:26:19 +02:00
src updated sid tune 2021-04-12 23:28:34 +02:00
util updated sid tune 2021-04-12 23:28:34 +02:00
.gitignore added distribution binary file .prg 2020-04-23 12:32:51 +02:00
.gitmodules compression routine for cartridge version, temporarily deprecates tape version 2020-10-04 17:51:35 +02:00
LICENSE.md updated LICENSE 2020-10-04 17:59:30 +02:00
Makefile disk and tape loader 2021-04-12 22:00:04 +02:00
README.md updated sid tune 2021-04-12 23:28:34 +02:00

README.md

snake6502

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

$ VERBOSE=1 make output useful info during compilation

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 - $07FF no free ram
$1000 - $1FFF yes SID tune
$2000 - $27FF yes custom char
$2800 - $xxxx yes Program segment (only needed part used)
$xxxx - $CCFF no free ram
$CD00 - $CDFF no data segment (not-initialized vars)
$CE00 - $CEFF no list X
$CF00 - $CFFF no list Y
$D000 - $DFFF no I/O
$E000 - $FFFF no Kernal

Compression

snake.pack is compressed into snake.pack.lz using liblzg, to save space in order to fit the game in a *PROM.

Decompression

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.

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 - game tiles