A7800DS/arm9/source/emu/ProSystem.c

// ----------------------------------------------------------------------------
//   ___  ___  ___  ___       ___  ____  ___  _  _
//  /__/ /__/ /  / /__  /__/ /__    /   /_   / |/ /
// /    / \  /__/ ___/ ___/ ___/   /   /__  /    /  emulator
//
// ----------------------------------------------------------------------------
// Copyright 2003, 2004 Greg Stanton
// 
// This program 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 2 of the License, or
// (at your option) any later version.
//
// This program 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 this program; if not, write to the Free Software
// Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
// ----------------------------------------------------------------------------
// ProSystem.cpp
// ----------------------------------------------------------------------------

#include "ProSystem.h"
#include "Database.h"

extern u8 isDS_LITE;
extern u8 frameSkipMask;

uint prosystem_cycles __attribute__((section(".dtcm"))) = 0;
uint32 bg32           __attribute__((section(".dtcm"))) = 0;
uint bRenderFrame     __attribute__((section(".dtcm"))) = 0;


#define CYCLES_BEFORE_DMA      28     // Number of cycles before DMA kicks in (really 7 CPU cycles)
#define CYCLES_PER_SCANLINE   454     // 454 Cycles per Scanline in an NTSC system (really 113.5 CPU cycles)


// ----------------------------------------------------------------------------
// Reset
// ----------------------------------------------------------------------------
void prosystem_Reset()
{
    if(cartridge_IsLoaded())
    {
        sally_Reset();
        region_Reset();
        tia_Clear();
        tia_Reset();
        pokey_Clear();
        pokey_Reset();
        memory_Reset();
        maria_Clear();
        maria_Reset();
        riot_Reset();
        cartridge_LoadHighScoreCart();

        cartridge_Store(); // Always call this - it may setup some RAM or other stuff below the BIOS region...

        // Load 7800 BIOS if available... otherwise direct load the CART
        if(bios_available && !bSkipBIOS)
        {
            bios_Store();
            bios_show_counter = myCartInfo.biosTimeout;
        }

        prosystem_cycles = sally_ExecuteRES();
    }
}


// ----------------------------------------------------------------------------
// ExecuteFrame - this is hand-tuned for NTSC output with hard-coded
// NTSC frame values ... this will not work properly if a PAL ROM is used.
// ----------------------------------------------------------------------------
ITCM_CODE void prosystem_ExecuteFrame(const byte * input)
{
    extern u16 gTotalAtariFrames;
    extern word * framePtr;
    extern uint maria_cycles;

    gTotalAtariFrames++;
    bRenderFrame = 0;

    riot_SetInput(input);

    // ---------------------------------------------------------------------
    // Handle the VERTICAL BLANK area first... speeds up processing below...
    // ---------------------------------------------------------------------
    memory_ram[MSTAT] = 128; // Into the Vertical Blank...  

    // -------------------------------------------------------------------------------------------  
    // Note: this is not accurate. It should be 263 scanlines total but it doesn't work for all
    // games at 263 so we've gone with 262 for maximum compatibility. This is likely due to some
    // emulation cycle counting inaccuracies. At 263, some games run too fast (Asteroids, Deluxe) 
    // and some crash (Robotron) and some issues with Pole Position II and the joystick selection
    // of a course to play. I've also seen graphical glitches in Crossbow when loaded via the 
    // BIOS and all kinds of graphical oddities in Xenophobe. Be very careful if you change this...
    // be sure you understand the consequences (and this developer doesn't... so be warned!).
    // -------------------------------------------------------------------------------------------    
    for(maria_scanline = 1; maria_scanline <= 21; maria_scanline++)
    {
        prosystem_cycles = 0;

        if(maria_scanline == 21) // Maria can start to do her thing... We've had 20 VBLANK scanlines
        {
            memory_ram[MSTAT] = 0; // Out of the vertical blank
            framePtr = (word * )(maria_surface);
            sally_Execute(CYCLES_BEFORE_DMA);

            maria_RenderScanlineTOP();

            // Cycle Stealing happens here...
            prosystem_cycles += ((maria_cycles + 3) >> 2) << 2; // Always a multiple of 4
            if(riot_and_wsync & 2) riot_UpdateTimer(maria_cycles >> 2);
        }
        else
        {
            sally_Execute(CYCLES_BEFORE_DMA);
        }

        sally_Execute(CYCLES_PER_SCANLINE);

        if(myCartInfo.pokeyType) // If pokey enabled, we process 1 pokey sample and 1 TIA sample. Good enough.
        {
            pokey_Process();
            pokey_Scanline();
        }
        else tia_Process(); // If all we have to deal with is the TIA, we can do so at 31KHz
    }

    // ------------------------------------------------------------
    // Now handle the Main display area...
    // ------------------------------------------------------------
    for(; maria_scanline < 263; maria_scanline++)
    {
        prosystem_cycles = 0;

        if(maria_scanline >= 30)
        {
            // --------------------------------------------------------------------------
            // We can start to render the scanlines if we are not skipping this frame.
            // The DS/DSi only has 192 vertical pixels and we can perform some hardware
            // scaling but there is a point at which we really can't show any more lines.
            // To that end, we'll render ~223 lines which is good enough for most games.
            // If a game uses more overscan area - those scanlines won't show on screen.
            // ---------------------------------------------------------------------------
            if(maria_scanline >= 253)
            {
                bRenderFrame = 0; // We can stop rendering frames... DS can't show it anyway with limited vertical resolution.
            }
            else
            {
                bRenderFrame = gTotalAtariFrames & frameSkipMask;
            }
        }

        sally_Execute(CYCLES_BEFORE_DMA);

        maria_RenderScanline();

        // Cycle Stealing happens here...
        prosystem_cycles += ((maria_cycles + 3) >> 2) << 2; // Always a multiple of 4
        if(riot_and_wsync & 2) riot_UpdateTimer(maria_cycles >> 2);

        sally_Execute(CYCLES_PER_SCANLINE);

        if(myCartInfo.pokeyType) // If pokey enabled, we process 1 pokey sample and 1 TIA sample. Good enough.
        {
            pokey_Process();
            pokey_Scanline();
        }
        else tia_Process(); // If all we have to deal with is the TIA, we can do so at 31KHz
    }
}

// ----------------------------------------------------------------------------
// Close
// ----------------------------------------------------------------------------
void prosystem_Close()
{
    cartridge_Release();
    maria_Reset();
    maria_Clear();
    memory_Reset();
    tia_Reset();
    tia_Clear();
}