Cool. I was thinking of making a gameboy emulator too but I'm too lazy. You might be interested in this java gb emulator, its got source code too.

Wow that was fast [smile]

The system itself is very simplistic, but still it takes a lot of patience to make an emulator. Building the CPU core takes a long time and even when it's "done", the chances of it working right are pretty slim.

I can't get that link to work, but I'd stick with the VisualBoyAdvance source anyway. It has both the GB and GBA, and is in C/C++. Thanks for trying to help though [smile]

How exactly do you load from ROMs? Do they present themselves as an extension to the available addresses in memory?

I'm not really sure what you're asking. Is it how the ROM memory works? I'll try to explain that.

The GB has 64KB of onboard memory. ROM can be 2MB in size and external RAM can be 128KB, both are located in the cartridge.

unsigned char *Memory[0x10];
unsigned char ROM[0x200000];
unsigned char RAM[0x20000];

The GB has 2 ROM banks, 16KB each in size, at 0x0000-0x7FFF. The first ROM bank is always bank 0(0x0000-0x3FFF of the ROM). On startup the second bank is set to ROM bank 1(0x4000-0x7FFF of the ROM, this can never be bank 0).

The GB has one 8KB RAM bank at 0xA000. At startup this is set to bank 0(0x0000-0x1FFF of external RAM).

So when I load a ROM(or memory dump):

Read each byte of the ROM file into ROM;
clear RAM;
Memory[0x0]=&ROM[0x0];
Memory[0x1]=&ROM[0x1000];
Memory[0x2]=&ROM[0x2000];
Memory[0x3]=&ROM[0x3000];
Memory[0x4]=&ROM[0x4000];
Memory[0x5]=&ROM[0x5000];
Memory[0x6]=&ROM[0x6000];
Memory[0x7]=&ROM[0x7000];
Memory[0xA]=&RAM[0x0];
Memory[0xB]=&RAM[0x1000];

To change the ROM bank(in say mapper #1) one must write a byte between 0x2000 and 0x3FFF. The lower 5 bits of that byte become the new address for bank 2(0x4000-0x7FFF).

RomBank=Value&0x1F;
if(RomBank==0){RomBank++;}
RomBank<<=14;
Memory[0x4]=&ROM[RomBank];
Memory[0x5]=&ROM[RomBank+0x1000];
Memory[0x6]=&ROM[RomBank+0x2000];
Memory[0x7]=&ROM[RomBank+0x3000];

It works in a somewhat similar fashiion for RAM switching. Basically to access the mappers and change banks, a byte with the right information is written to the onboard read-only memory at 0x0000-0x7FFF.