Step 0413: Fix STAT/LY/LCDC (PPU-MMIO) + LCD Toggle

⚙️ Implementation

Change 1: `PPU::get_stat()` - Dynamic STAT

Added methodget_stat()inPPU.cppwhich constructs the value of STAT dynamically:

uint8_t PPU::get_stat() const {
    // Step 0413: Build STAT dynamically
    // Bits 0-1: Current PPU mode
    uint8_t stat = mode_ & 0x03;
    
    // Bit 2: Match LYC=LY
    if (ly_ == lyc_) {
        stat |= 0x04;
    }
    
    // Bits 3-6: Interrupt masks (read from memory)
    // Bit 7: Always 1
    uint8_t stat_mem = mmu_->read(IO_STAT);
    stat |= (stat_mem & 0xF8);  // Preserve bits 3-7
    
    return stat;
}

Change 2: `MMU::read(0xFF41)` Use `get_stat()`

UpdatedMMU.cppso that when 0xFF41 is read, callppu_->get_stat():

// --- Step 0413: Dynamic STAT (Register 0xFF41) ---
if (addr == 0xFF41) {
    if (ppu_ != nullptr) {
        return ppu_->get_stat();
    }
    // If there is no PPU, return default value (mode 0, no match, bit 7 = 1)
    return (memory_[addr] & 0xF8) | 0x80;
}

Change 3: `PPU::handle_lcd_toggle()` - Timing Reset

Added methodhandle_lcd_toggle(bool lcd_on)inPPU.cpp:

void PPU::handle_lcd_toggle(bool lcd_on) {
    static int lcd_toggle_count = 0;
    
    if (lcd_on) {
        // LCD turns on: reset state at start of frame
        ly_ = 0;
        mode_ = MODE_2_OAM_SEARCH;
        clock_ = 0;
        scanline_rendered_ = false;
        
        // Update STAT to reflect mode 2
        uint8_t stat = mmu_->read(IO_STAT);
        stat = (stat & 0xFC) | MODE_2_OAM_SEARCH;  // Bits 0-1 = mode 2
        
        // Check LYC=LY match (must be LY=0)
        if (ly_ == lyc_) {
            stat |= 0x04;
        } else {
            stat &= ~0x04;
        }
        
        mmu_->write(IO_STAT, stat);
        
        if (lcd_toggle_count< 10) {
            printf("[PPU-LCD-TOGGLE] LCD turned ON | LY=%d Mode=%d STAT=0x%02X\n",
                   ly_, mode_, stat);
            lcd_toggle_count++;
        }
    } else {
        // LCD se apaga: forzar LY=0 y modo H-Blank
        ly_ = 0;
        mode_ = MODE_0_HBLANK;
        clock_ = 0;
        frame_ready_ = false;
        scanline_rendered_ = false;
        
        // Actualizar STAT para reflejar modo 0
        uint8_t stat = mmu_->read(IO_STAT);
        stat = (stat & 0xFC) | MODE_0_HBLANK;  // Bits 0-1 = mode 0
        
        // Clear LYC=LY match
        if (ly_ == lyc_) {
            stat |= 0x04;
        } else {
            stat &= ~0x04;
        }
        
        mmu_->write(IO_STAT, stat);
        
        if (lcd_toggle_count< 10) {
            printf("[PPU-LCD-TOGGLE] LCD turned OFF | LY=%d Mode=%d STAT=0x%02X\n",
                   ly_, mode_, stat);
            lcd_toggle_count++;
        }
    }
}

Change 4: Detect Toggle in `MMU::write(0xFF40)`

UpdatedMMU.cppto detect changes in LCDC bit 7 and callhandle_lcd_toggle():

if (addr == 0xFF40) {
    uint8_t old_lcdc = memory_[addr];
    uint8_t new_lcdc = value;
    
    if (old_lcdc != new_lcdc) {
        // Break down significant bits
        bool lcd_on_old = (old_lcdc & 0x80) != 0;
        bool lcd_on_new = (new_lcdc & 0x80) != 0;
        
        //...logging...
        
        // --- Step 0413: Detect LCD toggle (bit 7) ---
        if (lcd_on_old != lcd_on_new && ppu_ != nullptr) {
            ppu_->handle_lcd_toggle(lcd_on_new);
        }
        // -------------------------------------------
    }
}