melonDS/src/GPU.cpp

/*
    Copyright 2016-2019 Arisotura

    This file is part of melonDS.

    melonDS is free software: you can redistribute it and/or modify it under
    the terms of the GNU General Public License as published by the Free
    Software Foundation, either version 3 of the License, or (at your option)
    any later version.

    melonDS is distributed in the hope that it will be useful, but WITHOUT ANY
    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
    FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

    You should have received a copy of the GNU General Public License along
    with melonDS. If not, see http://www.gnu.org/licenses/.
*/

#include <stdio.h>
#include <string.h>
#include "NDS.h"
#include "GPU.h"
u64 vbltime;

namespace GPU
{

#define LINE_CYCLES  (355*6)
#define HBLANK_CYCLES (48+(256*6))
#define FRAME_CYCLES  (LINE_CYCLES * 263)

u16 VCount;
u32 NextVCount;
u16 TotalScanlines;

bool RunFIFO;

u16 DispStat[2], VMatch[2];

u8 Palette[2*1024];
u8 OAM[2*1024];

u8 VRAM_A[128*1024];
u8 VRAM_B[128*1024];
u8 VRAM_C[128*1024];
u8 VRAM_D[128*1024];
u8 VRAM_E[ 64*1024];
u8 VRAM_F[ 16*1024];
u8 VRAM_G[ 16*1024];
u8 VRAM_H[ 32*1024];
u8 VRAM_I[ 16*1024];
u8* VRAM[9] = {VRAM_A, VRAM_B, VRAM_C, VRAM_D, VRAM_E, VRAM_F, VRAM_G, VRAM_H, VRAM_I};

u8 VRAMCNT[9];
u8 VRAMSTAT;

u32 VRAMMap_LCDC;

u32 VRAMMap_ABG[0x20];
u32 VRAMMap_AOBJ[0x10];
u32 VRAMMap_BBG[0x8];
u32 VRAMMap_BOBJ[0x8];

u32 VRAMMap_ABGExtPal[4];
u32 VRAMMap_AOBJExtPal;
u32 VRAMMap_BBGExtPal[4];
u32 VRAMMap_BOBJExtPal;

u32 VRAMMap_Texture[4];
u32 VRAMMap_TexPal[8];

u32 VRAMMap_ARM7[2];

int FrontBuffer;
u32* Framebuffer[2][2];
int FBScale[2];
bool Accelerated;

GPU2D* GPU2D_A;
GPU2D* GPU2D_B;


bool Init()
{
    GPU2D_A = new GPU2D(0);
    GPU2D_B = new GPU2D(1);
    if (!GPU3D::Init()) return false;

    FrontBuffer = 0;
    Framebuffer[0][0] = NULL; Framebuffer[0][1] = NULL;
    Framebuffer[1][0] = NULL; Framebuffer[1][1] = NULL;
    FBScale[0] = -1; FBScale[1] = -1; Accelerated = false;
    SetDisplaySettings(0, 0, false);

    return true;
}

void DeInit()
{
    delete GPU2D_A;
    delete GPU2D_B;
    GPU3D::DeInit();

    if (Framebuffer[0][0]) delete[] Framebuffer[0][0];
    if (Framebuffer[0][1]) delete[] Framebuffer[0][1];
    if (Framebuffer[1][0]) delete[] Framebuffer[1][0];
    if (Framebuffer[1][1]) delete[] Framebuffer[1][1];
}

void Reset()
{
    VCount = 0;
    NextVCount = -1;
    TotalScanlines = 0;

    DispStat[0] = 0;
    DispStat[1] = 0;
    VMatch[0] = 0;
    VMatch[1] = 0;

    memset(Palette, 0, 2*1024);
    memset(OAM, 0, 2*1024);

    memset(VRAM_A, 0, 128*1024);
    memset(VRAM_B, 0, 128*1024);
    memset(VRAM_C, 0, 128*1024);
    memset(VRAM_D, 0, 128*1024);
    memset(VRAM_E, 0,  64*1024);
    memset(VRAM_F, 0,  16*1024);
    memset(VRAM_G, 0,  16*1024);
    memset(VRAM_H, 0,  32*1024);
    memset(VRAM_I, 0,  16*1024);

    memset(VRAMCNT, 0, 9);
    VRAMSTAT = 0;

    VRAMMap_LCDC = 0;

    memset(VRAMMap_ABG, 0, sizeof(VRAMMap_ABG));
    memset(VRAMMap_AOBJ, 0, sizeof(VRAMMap_AOBJ));
    memset(VRAMMap_BBG, 0, sizeof(VRAMMap_BBG));
    memset(VRAMMap_BOBJ, 0, sizeof(VRAMMap_BOBJ));

    memset(VRAMMap_ABGExtPal, 0, sizeof(VRAMMap_ABGExtPal));
    VRAMMap_AOBJExtPal = 0;
    memset(VRAMMap_BBGExtPal, 0, sizeof(VRAMMap_BBGExtPal));
    VRAMMap_BOBJExtPal = 0;

    memset(VRAMMap_Texture, 0, sizeof(VRAMMap_Texture));
    memset(VRAMMap_TexPal, 0, sizeof(VRAMMap_TexPal));

    VRAMMap_ARM7[0] = 0;
    VRAMMap_ARM7[1] = 0;

    for (int i = 0; i < (256*192)<<(FBScale[0]*2); i++)
    {
        Framebuffer[0][0][i] = 0xFFFFFFFF;
        Framebuffer[1][0][i] = 0xFFFFFFFF;
    }
    for (int i = 0; i < (256*192)<<(FBScale[1]*2); i++)
    {
        Framebuffer[0][1][i] = 0xFFFFFFFF;
        Framebuffer[1][1][i] = 0xFFFFFFFF;
    }

    GPU2D_A->Reset();
    GPU2D_B->Reset();
    GPU3D::Reset();

    int backbuf = FrontBuffer ? 0 : 1;
    GPU2D_A->SetFramebuffer(Framebuffer[backbuf][1]);
    GPU2D_B->SetFramebuffer(Framebuffer[backbuf][0]);
}

void Stop()
{
    memset(Framebuffer[0][0], 0, (256*192)<<(FBScale[0]*2));
    memset(Framebuffer[0][1], 0, (256*192)<<(FBScale[1]*2));
    memset(Framebuffer[1][0], 0, (256*192)<<(FBScale[0]*2));
    memset(Framebuffer[1][1], 0, (256*192)<<(FBScale[1]*2));
}

void DoSavestate(Savestate* file)
{
    file->Section("GPUG");

    file->Var16(&VCount);
    file->Var32(&NextVCount);
    file->Var16(&TotalScanlines);

    file->Var16(&DispStat[0]);
    file->Var16(&DispStat[1]);
    file->Var16(&VMatch[0]);
    file->Var16(&VMatch[1]);

    file->VarArray(Palette, 2*1024);
    file->VarArray(OAM, 2*1024);

    file->VarArray(VRAM_A, 128*1024);
    file->VarArray(VRAM_B, 128*1024);
    file->VarArray(VRAM_C, 128*1024);
    file->VarArray(VRAM_D, 128*1024);
    file->VarArray(VRAM_E,  64*1024);
    file->VarArray(VRAM_F,  16*1024);
    file->VarArray(VRAM_G,  16*1024);
    file->VarArray(VRAM_H,  32*1024);
    file->VarArray(VRAM_I,  16*1024);

    file->VarArray(VRAMCNT, 9);
    file->Var8(&VRAMSTAT);

    file->Var32(&VRAMMap_LCDC);

    file->VarArray(VRAMMap_ABG, sizeof(VRAMMap_ABG));
    file->VarArray(VRAMMap_AOBJ, sizeof(VRAMMap_AOBJ));
    file->VarArray(VRAMMap_BBG, sizeof(VRAMMap_BBG));
    file->VarArray(VRAMMap_BOBJ, sizeof(VRAMMap_BOBJ));

    file->VarArray(VRAMMap_ABGExtPal, sizeof(VRAMMap_ABGExtPal));
    file->Var32(&VRAMMap_AOBJExtPal);
    file->VarArray(VRAMMap_BBGExtPal, sizeof(VRAMMap_BBGExtPal));
    file->Var32(&VRAMMap_BOBJExtPal);

    file->VarArray(VRAMMap_Texture, sizeof(VRAMMap_Texture));
    file->VarArray(VRAMMap_TexPal, sizeof(VRAMMap_TexPal));

    file->Var32(&VRAMMap_ARM7[0]);
    file->Var32(&VRAMMap_ARM7[1]);

    GPU2D_A->DoSavestate(file);
    GPU2D_B->DoSavestate(file);
    GPU3D::DoSavestate(file);
}

void AssignFramebuffers()
{
    int backbuf = FrontBuffer ? 0 : 1;
    if (NDS::PowerControl9 & (1<<15))
    {
        GPU2D_A->SetFramebuffer(Framebuffer[backbuf][0]);
        GPU2D_B->SetFramebuffer(Framebuffer[backbuf][1]);
    }
    else
    {
        GPU2D_A->SetFramebuffer(Framebuffer[backbuf][1]);
        GPU2D_B->SetFramebuffer(Framebuffer[backbuf][0]);
    }
}

void SetDisplaySettings(int topscale, int bottomscale, bool accel)
{accel=true;
    if (topscale != FBScale[0] || accel != Accelerated)
    {
        FBScale[0] = accel ? 0 : topscale;

        int fbsize;
        if (accel) fbsize = (256*3 + 1) * 192;
        else       fbsize = (256 * 192) << (FBScale[0] * 2);
        if (Framebuffer[0][0]) delete[] Framebuffer[0][0];
        if (Framebuffer[1][0]) delete[] Framebuffer[1][0];
        Framebuffer[0][0] = new u32[fbsize];
        Framebuffer[1][0] = new u32[fbsize];

        memset(Framebuffer[0][0], 0, fbsize*4);
        memset(Framebuffer[1][0], 0, fbsize*4);

        int backbuf = FrontBuffer ? 0 : 1;
        if (NDS::PowerControl9 & (1<<15))
        {
            GPU2D_A->SetFramebuffer(Framebuffer[backbuf][0]);
            GPU2D_A->SetDisplaySettings(FBScale[0], accel);
            GPU3D::SetDisplaySettings(topscale, accel);
        }
        else
        {
            GPU2D_B->SetFramebuffer(Framebuffer[backbuf][0]);
            GPU2D_B->SetDisplaySettings(FBScale[0], accel);
        }
    }

    if (bottomscale != FBScale[1] || accel != Accelerated)
    {
        FBScale[1] = accel ? 0 : bottomscale;

        int fbsize;
        if (accel) fbsize = (256*3 + 1) * 192;
        else       fbsize = (256 * 192) << (FBScale[1] * 2);
        if (Framebuffer[0][1]) delete[] Framebuffer[0][1];
        if (Framebuffer[1][1]) delete[] Framebuffer[1][1];
        Framebuffer[0][1] = new u32[fbsize];
        Framebuffer[1][1] = new u32[fbsize];

        memset(Framebuffer[0][1], 0, fbsize*4);
        memset(Framebuffer[1][1], 0, fbsize*4);

        int backbuf = FrontBuffer ? 0 : 1;
        if (NDS::PowerControl9 & (1<<15))
        {
            GPU2D_B->SetFramebuffer(Framebuffer[backbuf][1]);
            GPU2D_B->SetDisplaySettings(FBScale[1], accel);
        }
        else
        {
            GPU2D_A->SetFramebuffer(Framebuffer[backbuf][1]);
            GPU2D_A->SetDisplaySettings(FBScale[1], accel);
            GPU3D::SetDisplaySettings(bottomscale, accel);
        }
    }

    Accelerated = accel;
}


// VRAM mapping notes
//
// mirroring:
// unmapped range reads zero
// LCD is mirrored every 0x100000 bytes, the gap between each mirror reads zero
// ABG:
//   bank A,B,C,D,E mirror every 0x80000 bytes
//   bank F,G mirror at base+0x8000, mirror every 0x80000 bytes
// AOBJ:
//   bank A,B,E mirror every 0x40000 bytes
//   bank F,G mirror at base+0x8000, mirror every 0x40000 bytes
// BBG:
//   bank C mirrors every 0x20000 bytes
//   bank H mirrors every 0x10000 bytes
//   bank I mirrors at base+0x4000, mirrors every 0x10000 bytes
// BOBJ:
//   bank D mirrors every 0x20000 bytes
//   bank I mirrors every 0x4000 bytes
//
// untested:
//   ARM7 (TODO)
//   extended palette (mirroring doesn't apply)
//   texture/texpal (does mirroring apply?)
//   -> trying to use extpal/texture/texpal with no VRAM mapped.
//      would likely read all black, but has to be tested.
//
// overlap:
// when reading: values are read from each bank and ORed together
// when writing: value is written to each bank

#define MAP_RANGE(map, base, n)  for (int i = 0; i < n; i++) map[(base)+i] |= bankmask;
#define UNMAP_RANGE(map, base, n)  for (int i = 0; i < n; i++) map[(base)+i] &= ~bankmask;

void MapVRAM_AB(u32 bank, u8 cnt)
{
    u8 oldcnt = VRAMCNT[bank];
    VRAMCNT[bank] = cnt;

    if (oldcnt == cnt) return;

    u8 oldofs = (oldcnt >> 3) & 0x3;
    u8 ofs = (cnt >> 3) & 0x3;
    u32 bankmask = 1 << bank;

    if (oldcnt & (1<<7))
    {
        switch (oldcnt & 0x3)
        {
        case 0: // LCDC
            VRAMMap_LCDC &= ~bankmask;
            break;

        case 1: // ABG
            UNMAP_RANGE(VRAMMap_ABG, oldofs<<3, 8);
            break;

        case 2: // AOBJ
            oldofs &= 0x1;
            UNMAP_RANGE(VRAMMap_AOBJ, oldofs<<3, 8);
            break;

        case 3: // texture
            VRAMMap_Texture[oldofs] &= ~bankmask;
            break;
        }
    }

    if (cnt & (1<<7))
    {
        switch (cnt & 0x3)
        {
        case 0: // LCDC
            VRAMMap_LCDC |= bankmask;
            break;

        case 1: // ABG
            MAP_RANGE(VRAMMap_ABG, ofs<<3, 8);
            break;

        case 2: // AOBJ
            ofs &= 0x1;
            MAP_RANGE(VRAMMap_AOBJ, ofs<<3, 8);
            break;

        case 3: // texture
            VRAMMap_Texture[ofs] |= bankmask;
            break;
        }
    }
}

void MapVRAM_CD(u32 bank, u8 cnt)
{
    u8 oldcnt = VRAMCNT[bank];
    VRAMCNT[bank] = cnt;

    VRAMSTAT &= ~(1 << (bank-2));

    if (oldcnt == cnt) return;

    u8 oldofs = (oldcnt >> 3) & 0x7;
    u8 ofs = (cnt >> 3) & 0x7;
    u32 bankmask = 1 << bank;

    if (oldcnt & (1<<7))
    {
        switch (oldcnt & 0x7)
        {
        case 0: // LCDC
            VRAMMap_LCDC &= ~bankmask;
            break;

        case 1: // ABG
            UNMAP_RANGE(VRAMMap_ABG, oldofs<<3, 8);
            break;

        case 2: // ARM7 VRAM
            oldofs &= 0x1;
            VRAMMap_ARM7[oldofs] &= ~bankmask;
            break;

        case 3: // texture
            VRAMMap_Texture[oldofs] &= ~bankmask;
            break;

        case 4: // BBG/BOBJ
            if (bank == 2)
            {
                UNMAP_RANGE(VRAMMap_BBG, 0, 8);
            }
            else
            {
                UNMAP_RANGE(VRAMMap_BOBJ, 0, 8);
            }
            break;
        }
    }

    if (cnt & (1<<7))
    {
        switch (cnt & 0x7)
        {
        case 0: // LCDC
            VRAMMap_LCDC |= bankmask;
            break;

        case 1: // ABG
            MAP_RANGE(VRAMMap_ABG, ofs<<3, 8);
            break;

        case 2: // ARM7 VRAM
            ofs &= 0x1;
            VRAMMap_ARM7[ofs] |= bankmask;
            VRAMSTAT |= (1 << (bank-2));
            break;

        case 3: // texture
            VRAMMap_Texture[ofs] |= bankmask;
            break;

        case 4: // BBG/BOBJ
            if (bank == 2)
            {
                MAP_RANGE(VRAMMap_BBG, 0, 8);
            }
            else
            {
                MAP_RANGE(VRAMMap_BOBJ, 0, 8);
            }
            break;
        }
    }
}

void MapVRAM_E(u32 bank, u8 cnt)
{
    u8 oldcnt = VRAMCNT[bank];
    VRAMCNT[bank] = cnt;

    if (oldcnt == cnt) return;

    u32 bankmask = 1 << bank;

    if (oldcnt & (1<<7))
    {
        switch (oldcnt & 0x7)
        {
        case 0: // LCDC
            VRAMMap_LCDC &= ~bankmask;
            break;

        case 1: // ABG
            UNMAP_RANGE(VRAMMap_ABG, 0, 4);
            break;

        case 2: // AOBJ
            UNMAP_RANGE(VRAMMap_AOBJ, 0, 4);
            break;

        case 3: // texture palette
            UNMAP_RANGE(VRAMMap_TexPal, 0, 4);
            break;

        case 4: // ABG ext palette
            UNMAP_RANGE(VRAMMap_ABGExtPal, 0, 4);
            GPU2D_A->BGExtPalDirty(0);
            GPU2D_A->BGExtPalDirty(2);
            break;
        }
    }

    if (cnt & (1<<7))
    {
        switch (cnt & 0x7)
        {
        case 0: // LCDC
            VRAMMap_LCDC |= bankmask;
            break;

        case 1: // ABG
            MAP_RANGE(VRAMMap_ABG, 0, 4);
            break;

        case 2: // AOBJ
            MAP_RANGE(VRAMMap_AOBJ, 0, 4);
            break;

        case 3: // texture palette
            MAP_RANGE(VRAMMap_TexPal, 0, 4);
            break;

        case 4: // ABG ext palette
            MAP_RANGE(VRAMMap_ABGExtPal, 0, 4);
            GPU2D_A->BGExtPalDirty(0);
            GPU2D_A->BGExtPalDirty(2);
            break;
        }
    }
}

void MapVRAM_FG(u32 bank, u8 cnt)
{
    u8 oldcnt = VRAMCNT[bank];
    VRAMCNT[bank] = cnt;

    if (oldcnt == cnt) return;

    u8 oldofs = (oldcnt >> 3) & 0x7;
    u8 ofs = (cnt >> 3) & 0x7;
    u32 bankmask = 1 << bank;

    if (oldcnt & (1<<7))
    {
        switch (oldcnt & 0x7)
        {
        case 0: // LCDC
            VRAMMap_LCDC &= ~bankmask;
            break;

        case 1: // ABG
            VRAMMap_ABG[(oldofs & 0x1) + ((oldofs & 0x2) << 1)] &= ~bankmask;
            VRAMMap_ABG[(oldofs & 0x1) + ((oldofs & 0x2) << 1) + 2] &= ~bankmask;
            break;

        case 2: // AOBJ
            VRAMMap_AOBJ[(oldofs & 0x1) + ((oldofs & 0x2) << 1)] &= ~bankmask;
            VRAMMap_AOBJ[(oldofs & 0x1) + ((oldofs & 0x2) << 1) + 2] &= ~bankmask;
            break;

        case 3: // texture palette
            VRAMMap_TexPal[(oldofs & 0x1) + ((oldofs & 0x2) << 1)] &= ~bankmask;
            break;

        case 4: // ABG ext palette
            VRAMMap_ABGExtPal[((oldofs & 0x1) << 1)] &= ~bankmask;
            VRAMMap_ABGExtPal[((oldofs & 0x1) << 1) + 1] &= ~bankmask;
            GPU2D_A->BGExtPalDirty((oldofs & 0x1) << 1);
            break;

        case 5: // AOBJ ext palette
            VRAMMap_AOBJExtPal &= ~bankmask;
            GPU2D_A->OBJExtPalDirty();
            break;
        }
    }

    if (cnt & (1<<7))
    {
        switch (cnt & 0x7)
        {
        case 0: // LCDC
            VRAMMap_LCDC |= bankmask;
            break;

        case 1: // ABG
            VRAMMap_ABG[(ofs & 0x1) + ((ofs & 0x2) << 1)] |= bankmask;
            VRAMMap_ABG[(ofs & 0x1) + ((ofs & 0x2) << 1) + 2] |= bankmask;
            break;

        case 2: // AOBJ
            VRAMMap_AOBJ[(ofs & 0x1) + ((ofs & 0x2) << 1)] |= bankmask;
            VRAMMap_AOBJ[(ofs & 0x1) + ((ofs & 0x2) << 1) + 2] |= bankmask;
            break;

        case 3: // texture palette
            VRAMMap_TexPal[(ofs & 0x1) + ((ofs & 0x2) << 1)] |= bankmask;
            break;

        case 4: // ABG ext palette
            VRAMMap_ABGExtPal[((ofs & 0x1) << 1)] |= bankmask;
            VRAMMap_ABGExtPal[((ofs & 0x1) << 1) + 1] |= bankmask;
            GPU2D_A->BGExtPalDirty((ofs & 0x1) << 1);
            break;

        case 5: // AOBJ ext palette
            VRAMMap_AOBJExtPal |= bankmask;
            GPU2D_A->OBJExtPalDirty();
            break;
        }
    }
}

void MapVRAM_H(u32 bank, u8 cnt)
{
    u8 oldcnt = VRAMCNT[bank];
    VRAMCNT[bank] = cnt;

    if (oldcnt == cnt) return;

    u32 bankmask = 1 << bank;

    if (oldcnt & (1<<7))
    {
        switch (oldcnt & 0x3)
        {
        case 0: // LCDC
            VRAMMap_LCDC &= ~bankmask;
            break;

        case 1: // BBG
            VRAMMap_BBG[0] &= ~bankmask;
            VRAMMap_BBG[1] &= ~bankmask;
            VRAMMap_BBG[4] &= ~bankmask;
            VRAMMap_BBG[5] &= ~bankmask;
            break;

        case 2: // BBG ext palette
            UNMAP_RANGE(VRAMMap_BBGExtPal, 0, 4);
            GPU2D_B->BGExtPalDirty(0);
            GPU2D_B->BGExtPalDirty(2);
            break;
        }
    }

    if (cnt & (1<<7))
    {
        switch (cnt & 0x3)
        {
        case 0: // LCDC
            VRAMMap_LCDC |= bankmask;
            break;

        case 1: // BBG
            VRAMMap_BBG[0] |= bankmask;
            VRAMMap_BBG[1] |= bankmask;
            VRAMMap_BBG[4] |= bankmask;
            VRAMMap_BBG[5] |= bankmask;
            break;

        case 2: // BBG ext palette
            MAP_RANGE(VRAMMap_BBGExtPal, 0, 4);
            GPU2D_B->BGExtPalDirty(0);
            GPU2D_B->BGExtPalDirty(2);
            break;
        }
    }
}

void MapVRAM_I(u32 bank, u8 cnt)
{
    u8 oldcnt = VRAMCNT[bank];
    VRAMCNT[bank] = cnt;

    if (oldcnt == cnt) return;

    u32 bankmask = 1 << bank;

    if (oldcnt & (1<<7))
    {
        switch (oldcnt & 0x3)
        {
        case 0: // LCDC
            VRAMMap_LCDC &= ~bankmask;
            break;

        case 1: // BBG
            VRAMMap_BBG[2] &= ~bankmask;
            VRAMMap_BBG[3] &= ~bankmask;
            VRAMMap_BBG[6] &= ~bankmask;
            VRAMMap_BBG[7] &= ~bankmask;
            break;

        case 2: // BOBJ
            UNMAP_RANGE(VRAMMap_BOBJ, 0, 8);
            break;

        case 3: // BOBJ ext palette
            VRAMMap_BOBJExtPal &= ~bankmask;
            GPU2D_B->OBJExtPalDirty();
            break;
        }
    }

    if (cnt & (1<<7))
    {
        switch (cnt & 0x3)
        {
        case 0: // LCDC
            VRAMMap_LCDC |= bankmask;
            break;

        case 1: // BBG
            VRAMMap_BBG[2] |= bankmask;
            VRAMMap_BBG[3] |= bankmask;
            VRAMMap_BBG[6] |= bankmask;
            VRAMMap_BBG[7] |= bankmask;
            break;

        case 2: // BOBJ
            MAP_RANGE(VRAMMap_BOBJ, 0, 8);
            break;

        case 3: // BOBJ ext palette
            VRAMMap_BOBJExtPal |= bankmask;
            GPU2D_B->OBJExtPalDirty();
            break;
        }
    }
}


void SetPowerCnt(u32 val)
{
    // POWCNT1 effects:
    // * bit0: asplodes hardware??? not tested.
    // * bit1: disables engine A palette and OAM (zero-filled) (TODO: affects mem timings???)
    // * bit2: disables rendering engine, resets its internal state (polygons and registers)
    // * bit3: disables geometry engine
    // * bit9: disables engine B palette, OAM and rendering (screen turns white)
    // * bit15: screen swap

    if (!(val & (1<<0))) printf("!!! CLEARING POWCNT BIT0. DANGER\n");

    GPU2D_A->SetEnabled(val & (1<<1));
    GPU2D_B->SetEnabled(val & (1<<9));
    GPU3D::SetEnabled(val & (1<<3), val & (1<<2));

    AssignFramebuffers();
}


void DisplayFIFO(u32 x)
{
    // sample the FIFO
    // as this starts 16 cycles (~3 pixels) before display start,
    // we aren't aligned to the 8-pixel grid
    if (x > 0)
    {
        if (x == 8)
            GPU2D_A->SampleFIFO(0, 5);
        else
            GPU2D_A->SampleFIFO(x-11, 8);
    }

    if (x < 256)
    {
        // transfer the next 8 pixels
        NDS::CheckDMAs(0, 0x04);
        NDS::ScheduleEvent(NDS::Event_DisplayFIFO, true, 6*8, DisplayFIFO, x+8);
    }
    else
        GPU2D_A->SampleFIFO(253, 3); // sample the remaining pixels
}

void StartFrame()
{
    // only run the display FIFO if needed:
    // * if it is used for display or capture
    // * if we have display FIFO DMA
    RunFIFO = GPU2D_A->UsesFIFO() || NDS::DMAsInMode(0, 0x04);

    TotalScanlines = 0;
    StartScanline(0);
}

void StartHBlank(u32 line)
{
    DispStat[0] |= (1<<1);
    DispStat[1] |= (1<<1);

    if (VCount < 192)
    {
        // draw
        // note: this should start 48 cycles after the scanline start
        if (line < 192)
        {
            GPU2D_A->DrawScanline(line);
            GPU2D_B->DrawScanline(line);
        }

        NDS::CheckDMAs(0, 0x02);
    }
    else if (VCount == 215)
    {
        GPU3D::VCount215();
    }

    if (DispStat[0] & (1<<4)) NDS::SetIRQ(0, NDS::IRQ_HBlank);
    if (DispStat[1] & (1<<4)) NDS::SetIRQ(1, NDS::IRQ_HBlank);

    if (VCount < 262)
        NDS::ScheduleEvent(NDS::Event_LCD, true, (LINE_CYCLES - HBLANK_CYCLES), StartScanline, line+1);
    else
        NDS::ScheduleEvent(NDS::Event_LCD, true, (LINE_CYCLES - HBLANK_CYCLES), FinishFrame, line+1);
}

void FinishFrame(u32 lines)
{
    FrontBuffer = FrontBuffer ? 0 : 1;
    AssignFramebuffers();

    TotalScanlines = lines;
}

void StartScanline(u32 line)
{
    if (line == 0)
        VCount = 0;
    else if (NextVCount != -1)
        VCount = NextVCount;
    else
        VCount++;

    NextVCount = -1;

    DispStat[0] &= ~(1<<1);
    DispStat[1] &= ~(1<<1);

    if (VCount == VMatch[0])
    {
        DispStat[0] |= (1<<2);

        if (DispStat[0] & (1<<5)) NDS::SetIRQ(0, NDS::IRQ_VCount);
    }
    else
        DispStat[0] &= ~(1<<2);

    if (VCount == VMatch[1])
    {
        DispStat[1] |= (1<<2);

        if (DispStat[1] & (1<<5)) NDS::SetIRQ(1, NDS::IRQ_VCount);
    }
    else
        DispStat[1] &= ~(1<<2);

    GPU2D_A->CheckWindows(VCount);
    GPU2D_B->CheckWindows(VCount);

    if (VCount >= 2 && VCount < 194)
        NDS::CheckDMAs(0, 0x03);
    else if (VCount == 194)
        NDS::StopDMAs(0, 0x03);

    if (line < 192)
    {
        if (line == 0)
        {
            GPU2D_A->VBlankEnd();
            GPU2D_B->VBlankEnd();
        }

        if (RunFIFO)
            NDS::ScheduleEvent(NDS::Event_DisplayFIFO, false, 32, DisplayFIFO, 0);
    }

    if (VCount == 262)
    {
        // frame end

        DispStat[0] &= ~(1<<0);
        DispStat[1] &= ~(1<<0);
    }
    else
    {
        if (VCount == 192)
        {
            // VBlank
            DispStat[0] |= (1<<0);
            DispStat[1] |= (1<<0);

            NDS::StopDMAs(0, 0x04);

            NDS::CheckDMAs(0, 0x01);
            NDS::CheckDMAs(1, 0x11);

            if (DispStat[0] & (1<<3)) NDS::SetIRQ(0, NDS::IRQ_VBlank);
            if (DispStat[1] & (1<<3)) NDS::SetIRQ(1, NDS::IRQ_VBlank);

            GPU2D_A->VBlank();
            GPU2D_B->VBlank();
            GPU3D::VBlank();
        }
        else if (VCount == 144)
        {
            GPU3D::VCount144();
        }
    }

    NDS::ScheduleEvent(NDS::Event_LCD, true, HBLANK_CYCLES, StartHBlank, line);
}


void SetDispStat(u32 cpu, u16 val)
{
    val &= 0xFFB8;
    DispStat[cpu] &= 0x0047;
    DispStat[cpu] |= val;

    VMatch[cpu] = (val >> 8) | ((val & 0x80) << 1);
}

void SetVCount(u16 val)
{
    // VCount write is delayed until the next scanline

    // TODO: how does the 3D engine react to VCount writes while it's rendering?
    // 3D engine seems to give up on the current frame in that situation, repeating the last two scanlines
    // TODO: also check the various DMA types that can be involved

    NextVCount = val;
}

}