mem.cpp

#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include "mem.h"
#include "rom.h"
#include "lcd.h"
#include "mbc.h"
#include "interrupt.h"
#include "timer.h"
#include "cpu.h"

bool usebootrom = false;
uint8_t *mem = nullptr;
static uint8_t *echo;
static uint32_t DMA_pending;
static uint8_t joypad_select_buttons, joypad_select_directions;
uint8_t btn_directions, btn_faces;
static const s_rominfo *rominfo;
static const uint8_t *rom;


uint8_t mem_get_byte(uint16_t i)
{
	if(DMA_pending && i < 0xFF80)
	{
		uint32_t elapsed = cpu_get_cycles() - DMA_pending;
		if(elapsed >= 160) {
			DMA_pending = 0;
		} else {
			return mem[0xFE00+elapsed];
		}
	}

	if(i >= 0x4000 && i < 0x8000)
		return rombank[i - 0x4000];

	else if (i >= 0xA000 && i < 0xC000)
		return mbc_read_ram(i);
	
	else if (i >= 0xE000 && i < 0xFE00)
		return echo[i];

	else switch(i)
	{
		case 0xFF00: {	/* Joypad */
			uint8_t mask = 0;
			if(!joypad_select_buttons)
				mask = btn_faces;
			if(!joypad_select_directions)
				mask = btn_directions;
			return (0xC0) | (joypad_select_buttons | joypad_select_directions) | (mask);
		}
		case 0xFF04: return timer_get_div();
		case 0xFF0F: return 0xE0 | IF;
		case 0xFF41: return lcd_get_stat();
		case 0xFF44: return lcd_get_line();
		case 0xFF4D: return 0xFF; /* GBC speed switch */
		case 0xFFFF: return IE;
	}

	return mem[i];
}

void mem_write_byte(uint16_t d, uint8_t i)
{
	/* ROM */
	if (d < 0x8000)
		mbc_write_rom(d, i);
	
	/* SRAM */
	else if (d >= 0xA000 && d < 0xC000)
		mbc_write_ram(d, i);
	
	/* ECHO */
	else if (d >= 0xE000 && d < 0xFE00)
		echo[d] = i;

	else switch(d)
	{
		case 0xFF00:	/* Joypad */
			joypad_select_buttons = i&0x20;
			joypad_select_directions = i&0x10;
		break;
		case 0xFF04: timer_reset_div(); break;
		case 0xFF07: timer_set_tac(i); break;
		case 0xFF0F: IF = i; break;
		case 0xFF40: lcd_write_control(i); break;
		case 0xFF41: lcd_write_stat(i); break;
		case 0xFF42: lcd_write_scroll_y(i); break;
		case 0xFF43: lcd_write_scroll_x(i); break;
		case 0xFF44: lcd_reset(); break;
		case 0xFF45: lcd_set_ly_compare(i); break;
		case 0xFF46: { /* OAM DMA */
			/* Check if address overlaps with RAM or ROM */
			uint16_t addr = i * 0x100;
			const uint8_t* src = mem;
			if (addr >= 0x4000 && addr < 0x8000) {
				src = rombank;
				addr -= 0x4000;
			}
			else if (addr >= 0xA000 && addr < 0xC000) {
				src = rambank;
				addr -= 0xA000;
			}
			
			/* Copy 0xA0 bytes from source to OAM */
			memcpy(&mem[0xFE00], &src[addr], 0xA0);
			DMA_pending = cpu_get_cycles();
			break;
		}
		case 0xFF47: lcd_write_bg_palette(i); break;
		case 0xFF48: lcd_write_spr_palette1(i); break;
		case 0xFF49: lcd_write_spr_palette2(i); break;
		case 0xFF4A: lcd_set_window_y(i); break;
		case 0xFF4B: lcd_set_window_x(i); break;
		case 0xFF50: memcpy(&mem[0x0000], &rom[0x0000], 0x100); break; /* Lock bootROM */
		case 0xFFFF: IE = i; break;

		default: mem[d] = i; break;
	}
}

bool mmu_init(const uint8_t* bootrom)
{
	mem = (uint8_t *)calloc(1, 0x10000);
	if (!mem)
		return false;
	
	if (!mbc_init())
		return false;
	
	rom = rom_getbytes();
	echo = mem + 0xC000 - 0xE000;
	
	if (bootrom) {
		memcpy(&mem[0x0000], &bootrom[0x0000], 0x100);
		memcpy(&mem[0x0100], &rom[0x0100], 0x4000 - 0x100);
		usebootrom = true;
		return true;
	}
	
	// First ROM bank is always in RAM
	memcpy(&mem[0x0000], &rom[0x0000], 0x4000);

	// Default values if bootrom is not present
	mem[0xFF10] = 0x80;
	mem[0xFF11] = 0xBF;
	mem[0xFF12] = 0xF3;
	mem[0xFF14] = 0xBF;
	mem[0xFF16] = 0x3F;
	mem[0xFF19] = 0xBF;
	mem[0xFF1A] = 0x7F;
	mem[0xFF1B] = 0xFF;
	mem[0xFF1C] = 0x9F;
	mem[0xFF1E] = 0xBF;
	mem[0xFF20] = 0xFF;
	mem[0xFF23] = 0xBF;
	mem[0xFF24] = 0x77;
	mem[0xFF25] = 0xF3;
	mem[0xFF26] = 0xF1;
	mem[0xFF40] = 0x91;
	mem[0xFF47] = 0xFC;
	mem[0xFF48] = 0xFF;
	mem[0xFF49] = 0xFF;
	
	return true;
}