gb6/src/dmg.c

#include <stdio.h>
#include <string.h>

#include "cpu.h"
#include "rom.h"
#include "lcd.h"
#include "dmg.h"
#include "types.h"
#include "bootstrap.h"

void dmg_new(struct dmg *dmg, struct cpu *cpu, struct rom *rom, struct lcd *lcd)
{
    dmg->cpu = cpu;
    dmg->rom = rom;
    dmg->lcd = lcd;

    dmg->joypad = 0xf; // nothing pressed
    dmg->action_buttons = 0xf;
}

void dmg_set_button(struct dmg *dmg, int field, int button, int pressed)
{
    u8 *mod;
    if (field == FIELD_JOY) {
        mod = &dmg->joypad;
    } else if (field == FIELD_ACTION) {
        mod = &dmg->action_buttons;
    } else {
        printf("setting invalid button state\n");
        return;
    }

    if (pressed) {
        *mod &= ~button;
    } else {
        *mod |= button;
    }
}

static u8 get_button_state(struct dmg *dmg)
{
    return dmg->action_selected ? dmg->action_buttons : dmg->joypad;
}

u8 dmg_read(void *_dmg, u16 address)
{
    struct dmg *dmg = (struct dmg *) _dmg;
//    if (address < 0x100) {
//        return dmg_boot_rom[address];
//    } else if (address < 0x4000) {
    if (address < 0x4000) {
        return dmg->rom->data[address];
    } else if (address < 0x8000) {
        // TODO switchable rom bank
        return dmg->rom->data[address];
    } else if (address < 0xa000) {
        return dmg->video_ram[address - 0x8000];
    } else if (address < 0xc000) {
        // TODO switchable ram bank
        return 0;
    } else if (address < 0xe000) {
        return dmg->main_ram[address - 0xc000];
    } else if (lcd_is_valid_addr(address)) {
        return lcd_read(dmg->lcd, address);
    } else if (address >= 0xff80 && address <= 0xfffe) {
        return dmg->zero_page[address - 0xff80];
    } else if (address == 0xff00) {
        return get_button_state(dmg);
    } else if (address == 0xff0f) {
        return dmg->interrupt_requested;
    } else if (address == 0xffff) {
        return dmg->interrupt_enabled;
    } else {
        // not sure about any of this yet
        // commented out bc of memory view window
        // fprintf(stderr, "don't know how to read 0x%04x\n", address);
        return 0;
    }
}

void dmg_write(void *_dmg, u16 address, u8 data)
{
    struct dmg *dmg = (struct dmg *) _dmg;
    if (address < 0x4000) {
        printf("warning: writing 0x%04x in rom\n", address);
        dmg->rom->data[address] = data;
    } else if (address < 0x8000) {
        // TODO switchable rom bank
        printf("warning: writing 0x%04x in rom\n", address);
        dmg->rom->data[address] = data;
    } else if (address < 0xa000) {
        dmg->video_ram[address - 0x8000] = data;
    } else if (address < 0xc000) {
        // TODO switchable ram bank
    } else if (address < 0xe000) {
        dmg->main_ram[address - 0xc000] = data;
    } else if (lcd_is_valid_addr(address)) {
        lcd_write(dmg->lcd, address, data);
    } else if (address >= 0xff80 && address <= 0xfffe) {
        dmg->zero_page[address - 0xff80] = data;
    } else if (address == 0xff00) {
        dmg->action_selected = data & (1 << 5);
    } else if (address == 0xff0f) {
        dmg->interrupt_requested = data;
    } else if (address == 0xffff) {
        dmg->interrupt_enabled = data;
    } else {
        // not sure about any of this yet
    }
}

void dmg_request_interrupt(struct dmg *dmg, int nr)
{
    dmg->interrupt_requested |= nr;
}

void dmg_step(void *_dmg)
{
    struct dmg *dmg = (struct dmg *) _dmg;

    // order of dependencies? i think cpu needs to step first then update
    // all other hw
    cpu_step(dmg->cpu);

    // each line takes 456 cycles
    if (dmg->cpu->cycle_count - dmg->last_lcd_update >= 456) {
        dmg->last_lcd_update = dmg->cpu->cycle_count;
        int next_scanline = lcd_step(dmg->lcd);
        if (next_scanline == 144) {
            // vblank has started, draw all the stuff from ram into the lcd
            dmg_request_interrupt(dmg, INT_VBLANK);

            int lcdc = lcd_read(dmg->lcd, REG_LCDC);
            int bg_base = (lcdc & LCDC_BG_TILE_MAP) ? 0x9c00 : 0x9800;
            int window_base = (lcdc & LCDC_WINDOW_TILE_MAP) ? 0x9c00 : 0x9800;
            int use_unsigned = lcdc & LCDC_BG_TILE_DATA;
            int tilebase = use_unsigned ? 0x8000 : 0x9000;

            int k = 0, off = 0;
            int tile_y = 0, tile_x = 0;
            for (tile_y = 0; tile_y < 32; tile_y++) {
                for (tile_x = 0; tile_x < 32; tile_x++) {
                    off = 256 * 8 * tile_y + 8 * tile_x;
                    int tile = dmg_read(dmg, bg_base + (tile_y * 32 + tile_x));
                    int eff_addr;
                    if (use_unsigned) {
                        eff_addr = tilebase + 16 * tile;
                    } else {
                        eff_addr = tilebase + 16 * (signed char) tile;
                    }
                    int b, i;
                    for (b = 0; b < 16; b += 2) {
                        int data1 = dmg_read(dmg, eff_addr + b);
                        int data2 = dmg_read(dmg, eff_addr + b + 1);
                        for (i = 7; i >= 0; i--) {
                            // monochrome for now
                            dmg->lcd->buf[off] = (data1 & (1 << i)) ? 1 : 0;
                            //dmg->lcd->buf[off] |= (data2 & (1 << i)) ? 1 : 0;
                            off++;
                        }
                        off += 248;
                    }
                }
            }

            // now copy 256x256 buf to 160x144 based on window registers
            lcd_copy(dmg->lcd);
            lcd_draw(dmg->lcd);
        }
    }
}