I'm writing a CHIP-8 emulator, and have a lot of questions.

Anikom15 · 12-20-2009, 12:43 PM

I'm writing it in C. Here's the current code: (it's a work in progress)

Code:

#include <stdio.h>

main()
{
	unsigned int memory[0xfff];
	unsigned int stack[0xf];
	unsigned int V[0xf];
	unsigned int I;
	unsigned int delay = 0;
	unsigned int sound = 0;
	unsigned int PC;
	unsigned int SP;
	unsigned int opcode;

	unsigned int xres = 64;
	unsigned int yres = 32;

	for(;;) {
		opcode = memory[PC++];

		switch (opcode) {
			case 0x0:
				if ((opcode& 0x00ff) == 0xe0) {
					/* Clear display */
					break;
				}
				if ((opcode& 0x00ff) == 0xee) {
					/* Return from a subroutine */
					break;
				}
				break;
			case 0x1:
				/* Jump to 0x0fff */
				PC = opcode& 0x0fff;
				break;
			case 0x2:
				/* Call CHIP-8 sub-routine at 0x0fff */
				break;
		}
		PC += 2;
	}

	printf("Bye.\n");
	return 0;
}

1. What's the best method for doing the graphics and sound?

2. What's the "sub-routine" and how do I implement it?

3. How do I load a ROM file from the commandline like this:

Code:

$ <executable> <romfilename>

Thx.

smeezekitty · 12-20-2009, 01:11 PM

Quote:

What's the best method for doing the graphics and sound?

SDL or switch to MS-DOS.

Quote:

What's the "sub-routine" and how do I implement it

you put the value of PC+sizeof(procedure-opcode) on the stack then incrment the stack pointer.
when you return, you deincrment the stack pointer and jump to the address at STACK + SP.

Quote:

How do I load a ROM file from the commandline like this:

main (int argc, char **argv){}
argv is a list of strings passed on the command line.

Anikom15 · 12-20-2009, 01:53 PM

Ok. I can get it from the commandline, but how do I put the ROM information into the emulator's "memory"?

smeezekitty · 12-20-2009, 04:30 PM

Code:

FILE *f = fopen(argv[1], "rb");
fread(&memory, 1, 4096, f);
fclose(f);

That will load the file into the emulators memory.

Anikom15 · 12-21-2009, 12:30 PM

Ok, what should the value of "procedure" be?

Anikom15 · 12-21-2009, 05:46 PM

Sorry, double post.

Anikom15 · 12-21-2009, 05:47 PM

Ok, here's a snippet of code:

Code:

case 0xd:
/* Some sprite drawing! */
	for (n = (opcode& 0x000f); n > 0; n--) {
		len = 0;
		PC = memory[I];
		while (len <= 8) {
			putpixel(screen, V[opcode& 0x0f00] + len, V[opcode& 0x00f0] + n, color1);
			len++;
		}
	}
break;

How can I test if a color1 (white) pixel has replaced another white pixel? How can I wrap a sprite around to the other side of the screen if it's too long?

smeezekitty · 12-21-2009, 06:11 PM

Quote:

Originally Posted by Anikom15

Ok, here's a snippet of code:

Code:

case 0xd:
/* Some sprite drawing! */
	for (n = (opcode& 0x000f); n > 0; n--) {
		len = 0;
		PC = memory[I];
		while (len <= 8) {
			putpixel(screen, V[opcode& 0x0f00] + len, V[opcode& 0x00f0] + n, color1);
			len++;
		}
	}
break;

How can I test if a color1 (white) pixel has replaced another white pixel?

you cannot, unless you 'get' a pixel

Quote:

How can I wrap a sprite around to the other side of the screen if it's too long?

Code:

case 0xd:
/* Some sprite drawing! */

	for (n = (opcode& 0x000f); n > 0; n--) {
int wrapx=0,wrapy=0;
while(V[opcode& 0x0f00]+ len - wrapx >  [screen-width]/*replace this*/){wrapx += [screen-width]; /*replace this*/}
while(V[opcode& 0x00f0]+ n - wrapy > [screen-height]/*replace this*/){wrapy += [screen-height]; /*replace this*/}

		len = 0;
		PC = memory[I];
		while (len <= 8) {
			putpixel(screen, V[opcode& 0x0f00] + len - wrapx, V[opcode& 0x00f0] + n - wrapy, color1);
			len++;
		}
	}
break;

Anikom15 · 12-22-2009, 01:16 PM

Ok how do I implement this opcode:

Quote:

Fx33 - LD B, Vx
Store BCD representation of Vx in memory locations I, I+1, and I+2.

The interpreter takes the decimal value of Vx, and places the hundreds digit in memory at location in I, the tens digit at location I+1, and the ones digit at location I+2.

And I need to scale the entire surface (screen) by 10.

SS-00 · 12-23-2009, 01:23 PM

HeLLo
SoRRy for my post
I want to programming CHIP8 but I want someone explain to me how do that with c++ and sdl i tried before but i can't
please I want someone start and Explain it Line by line
I know CHIP8 instructions
I wait for your answer smeezekitty and Anikom15

Anikom15 · 12-23-2009, 01:47 PM

You want to program Chip-8 games? You'll need a chip-8 assembler, I don't know if any exist for linux.

SS-00 · 12-23-2009, 05:28 PM

thank you for your reply
what i want is how I write a CHIP8 Emulator like what are you doing now I want you tou explain to me each line for your program.i know how chip8 work and its component
I hope that does not hinder smeezekitty to help you

smeezekitty · 12-23-2009, 05:37 PM

Quote:

Ok how do I implement this opcode:
Quote:
Fx33 - LD B, Vx
Store BCD representation of Vx in memory locations I, I+1, and I+2.
The interpreter takes the decimal value of Vx, and places the hundreds digit in memory at location in I, the tens digit at location I+1, and the ones digit at location I+2.

Just a guess:

Code:

unsigned char digits[10];
itoa(V[PC+1], digits, 10);
V[I+2] = digits[strlen(digits)] - '0';
V[I+1] = digits[strlen(digits)-1] - '0';
V[I] = digits[strlen(digits]-2] - '0';

Of cource i did not include the switch case, etc.

Anikom15 · 12-23-2009, 11:47 PM

Quote:

Originally Posted by SS-00

thank you for your reply
what i want is how I write a CHIP8 Emulator like what are you doing now I want you tou explain to me each line for your program.i know how chip8 work and its component
I hope that does not hinder smeezekitty to help you

Well, I say read this first.

Then this.

You can take any code of mine if you wish, though it doesn't work yet.