kgabis/agnes

NES emulation library with an easy to use API.

agnes's Issues

Non mirrored CHR banks causes out of bounds memory access

I created a ROM that can crash the emulator or allow it to access out of bounds memory.

The ROM essentially writes a value from 0 to 255 to the MMC3 CHR banks registers, then increments this value every frame.

If the ROM has just one bank, the expected behavior is for that one bank to be mirrored.

I fixed it in the tool I included agnes in with modulus at the mapper level, but this breaks CHR RAM and doesn't properly respect powers of two for mirroring.

	int modValue = mapper->agnes->gamepack.chr_rom_banks_count*8;
    switch (mapper->chr_mode) {
        case 0: { // R0_1, R0_2, R1_1, R1_2, R2, R3, R4, R5
            mapper->chr_bank_offsets[0] = ((mapper->regs[0]%modValue) & 0xfe) * 1024;
			//similar modulus for all other lines

A real fix would probably be to allocate memory to the next power of two at load (for weird CHR bank values like 3 rather than 4), then AND instead of %

I've attached the ROM (It is homebrew, not commercial):
anim.zip

Why doesn't this include audio?

I know it's hard to make this library, but I'm just wondering why audio was never implemented

Why header only?

The concept of NES emulation library is great.
I think release it as a dynamically linked library is good enough, why restrict to header-only?