Snake on Commodore 64 Commodore 64 was a popular computer during the eighties. It's is still possible to get hold of one; Either by buying a vintage computer from an auction site or you could get a reproduction made with modern technology. If you do not want the real-thing, you could use an emulator We will make the game snake or nibbles on the c64. Snake is a well-known game that have been available in many platforms, lately also on playstation 3. This tutorial will be on Linux, but don't worry, we will show how you can easily use Linux from either Windows or Mac OSX.

Step 1 Download vmware player; http://www.vmware.com/products/player/

Step 2 You going to need a virtual applicance that will run from vmware player. We use this one; http://www.quotrader.org/vm/ubuntu1004/ If you do not want to follow step 1 to Step 7 it's possible to get a pre-installed version from us (post@retrotard.com)

Step 3 Start-up the downloaded vmware image, you will be prompted from a password, which (if you downloaded some of the above images) is "password"

Step 4 Next we need to install a c64 emulator. Start up a terminal, then type: sudo apt-get install vice This will install a c64 emulator. In addition for this emulator, vice, we also need to install some rom files. Start firefox browser inside your Linux, and go to http://www.zimmers.net/anonftp/pub/cbm/crossplatform/emulators/VICE/old/index.html Download: vice-0.14.2-roms.tar.gz Locate the downloaded files, usually by typing the following in the terminal: cd /home/user/Downloads Extract the files by typing: tar -xvfz vice-0.14.2-roms.tar.gz Next copy the rom files so the emulator can find them sudo cp * /usr/lib/vice/C64/. type: x64 to start the emulator

Step 5 Let's play around with the emulator, type poke 53281,0 inside the emulator Try to change 0 to a number between 0 and 15. poke means, place a value in memory, and by placing 0 at position 54281 in memory we change the color of the screen.

Step 6 We could go ahead an write snake in the built in basic on the c64, but that wouldn't be very satisfying. We could also find an assembler, but that would be a bit to detailed. The cool thing would be to build it on your host computer (linux) and send it to the c64 emulator. Luckily for us, there is a C compiler that produces c64 binaries that are compatible with the emulator. go to : ftp://ftp.musoftware.de/pub/uz/cc65/ download: cc65-sources-2.13.2.tar.bz2 and cc65-c64-2.13.2-1.zip Locate the downloaded files, and extract them with: tar -xvf cc65-sources-2.13.2.tar.bz2 and unzip cc65-c64-2.13.2-1.zip

Step 7 Locate the extracted directory cc65-2.13.2 cd cc65-2.13.2 Then type: sudo make -f make/gcc.mak Then sudo make -f make/gcc.mak install Now your development environment should be all set up. If you want to skip this part, you could get the vmware file from here

Step 8 Open gedit to type in the program gedit snake.c & type in (or copy and paste) the following code into gedit: /* SNAKE FOR C-64 */ #include <stdio.h> #include <stdlib.h> #define POKE(addr,val) (*(unsigned char*) (addr) = (val)) #define POKEW(addr,val) (*(unsigned*) (addr) = (val)) #define PEEK(addr) (*(unsigned char*) (addr)) #define PEEKW(addr) (*(unsigned*) (addr)) int key; int apples = 10; int applep[10][2]; int snakesize = 5; int snakesizep[40*25][2]; int px=20; int py=12; int ax=0; int ay=1; int tmp1; int tmp2; int tmp3; int tmp4; int main(void){ unsigned int i; POKE(53281,0); POKE(53272,21); for(i=0;i<40*25;i++){snakesizep[i][0]=snakesizep[i][1]=-1;} for(i=0;i<(40*25);i++){POKE(1024+i,32);} for(i=0;i<apples;i++){ applep[i][0] = rand()%40; applep[i][1] = rand()%25; POKE(1024+(applep[i][0]+applep[i][1]*40),36); POKE(55296+(applep[i][0]+applep[i][1]*40),2); } while(1){ POKE(1024+(snakesizep[snakesize-1][0]+snakesizep[snakesize-1][1]*40),32); POKE(55296+(snakesizep[snakesize-1][0]+snakesizep[snakesize-1][1]*40),0); key = PEEK(56320); if(key == 126){ ay=-1; ax=0; } else if(key == 125){ ay=1; ax=0; } else if(key == 123){ ay=0; ax=-1; } else if(key == 119){ ay=0; ax=1; } px+=ax; py+=ay; px%=40; py%=25; if(px<0){px=39;} if(py<0){py=24;} for(i=0;i<snakesize;i++){ if(snakesizep[i][0] == px && snakesizep[i][1] == py){ return 1; } } for(i=0;i<apples;i++){ if(applep[i][0] == px && applep[i][1] == py){ snakesize++; applep[i][0]=rand()%40; applep[i][1]=rand()%25; POKE(1024+(applep[i][0]+applep[i][1]*40),36); POKE(55296+(applep[i][0]+applep[i][1]*40),2); break; } } tmp3 = px; tmp4 = py; for(i=0;i<snakesize;i++){ tmp1 = snakesizep[i][0]; tmp2 = snakesizep[i][1]; snakesizep[i][0]=tmp3; snakesizep[i][1]=tmp4; tmp3 = tmp1; tmp4 = tmp2; } for(i=0;i<snakesize;i++){ if(snakesizep[i][0]!=-1){ POKE(1024+(snakesizep[i][0]+snakesizep[i][1]*40),42); POKE(55296+(snakesizep[i][0]+snakesizep[i][1]*40),5); } } } return EXIT_SUCCESS; } Save the file, and type: cc65 -O -t c64 snake.c Then ca65 snake.s and finally: ld65 -t c64 -o snake snake.o lib/c64.lib Where c64 lib is found in the directoy of the zip file

Step 9 Now let's try out the game: x64 snake which should make something like this:

Conclusion The game is played by setting the joystick in port no.2 For an interactive video guide, contact us post@retrotard.com