6502/EightBit
1
0
Fork 0
mirror of https://github.com/MoleskiCoder/EightBit.git synced 2026-04-26 06:17:47 +00:00
Code Issues Projects Releases Wiki Activity

Tidy the gameboy core a little. Mainly by moving the execution loops into the bus class.

Browse Source 
Signed-off-by: Adrian Conlon <Adrian.conlon@gmail.com>
This commit is contained in:
Adrian Conlon
2017-10-24 00:04:13 +01:00
parent 774b181008
commit a22e59546b
8 changed files with 155 additions and 154 deletions
Download Patch File Download Diff File Expand all files Collapse all files
LR35902/src/GameBoyBus.cpp
+112 -5
View File
@@ -1,5 +1,6 @@
#include "stdafx.h"
#include "GameBoyBus.h"
#include "Display.h"
EightBit::GameBoy::Bus::Bus()
: m_cpu(*this),
@@ -10,6 +11,7 @@ EightBit::GameBoy::Bus::Bus()
m_lowInternalRam(0x2000),
m_oamRam(0xa0),
m_ioPorts(*this),
m_enabledLCD(false),
m_highInternalRam(0x80),
m_disableGameRom(false),
m_rom(false),
@@ -24,8 +26,8 @@ EightBit::GameBoy::Bus::Bus()
}
void EightBit::GameBoy::Bus::reset() {
m_ioPorts.reset();
m_cpu.initialise();
IO().reset();
CPU().initialise();
}
void EightBit::GameBoy::Bus::loadBootRom(const std::string& path) {
@@ -113,7 +115,7 @@ void EightBit::GameBoy::Bus::validateCartridgeType() {
// ROM size
{
size_t gameRomBanks = 0;
int romSizeSpecification = m_gameRomBanks[0].peek(0x148);
const int romSizeSpecification = m_gameRomBanks[0].peek(0x148);
switch (romSizeSpecification) {
case 0x52:
gameRomBanks = 72;
@@ -166,7 +168,7 @@ void EightBit::GameBoy::Bus::validateCartridgeType() {
uint8_t& EightBit::GameBoy::Bus::reference(uint16_t address, bool& rom) {
rom = true;
if ((address < 0x100) && m_ioPorts.bootRomEnabled())
if ((address < 0x100) && IO().bootRomEnabled())
return m_bootRom.reference(address);
if ((address < 0x4000) && gameRomEnabled())
return m_gameRomBanks[0].reference(address);
@@ -187,6 +189,111 @@ uint8_t& EightBit::GameBoy::Bus::reference(uint16_t address, bool& rom) {
if (address < IoRegisters::BASE)
return rom = true, placeDATA(0xff);
if (address < 0xff80)
return m_ioPorts.reference(address - IoRegisters::BASE);
return IO().reference(address - IoRegisters::BASE);
return m_highInternalRam.reference(address - 0xff80);
}
int EightBit::GameBoy::Bus::runRasterLines() {
m_enabledLCD = !!(IO().peek(IoRegisters::LCDC) & IoRegisters::LcdEnable);
IO().resetLY();
return runRasterLines(Display::RasterHeight);
}
int EightBit::GameBoy::Bus::runRasterLines(int lines) {
int count = 0;
int allowed = CyclesPerLine;
for (int line = 0; line < lines; ++line) {
auto executed = runRasterLine(allowed);
count += executed;
allowed = CyclesPerLine - (executed - CyclesPerLine);
}
return count;
}
int EightBit::GameBoy::Bus::runRasterLine(int limit) {
/*
A scanline normally takes 456 clocks (912 clocks in double speed
mode) to complete. A scanline starts in mode 2, then goes to
mode 3 and, when the LCD controller has finished drawing the
line (the timings depend on lots of things) it goes to mode 0.
During lines 144-153 the LCD controller is in mode 1.
Line 153 takes only a few clocks to complete (the exact
timings are below). The rest of the clocks of line 153 are
spent in line 0 in mode 1!
During mode 0 and mode 1 the CPU can access both VRAM and OAM.
During mode 2 the CPU can only access VRAM, not OAM.
During mode 3 OAM and VRAM can't be accessed.
In GBC mode the CPU can't access Palette RAM(FF69h and FF6Bh)
during mode 3.
A scanline normally takes 456 clocks(912 clocks in double speed mode) to complete.
A scanline starts in mode 2, then goes to mode 3 and , when the LCD controller has
finished drawing the line(the timings depend on lots of things) it goes to mode 0.
During lines 144 - 153 the LCD controller is in mode 1.
Line 153 takes only a few clocks to complete(the exact timings are below).
The rest of the clocks of line 153 are spent in line 0 in mode 1!
*/
int count = 0;
if (m_enabledLCD) {
if ((IO().peek(IoRegisters::STAT) & Processor::Bit6) && (IO().peek(IoRegisters::LYC) == IO().peek(IoRegisters::LY)))
IO().triggerInterrupt(IoRegisters::Interrupts::DisplayControlStatus);
// Mode 2, OAM unavailable
IO().updateLcdStatusMode(IoRegisters::LcdStatusMode::SearchingOamRam);
if (IO().peek(IoRegisters::STAT) & Processor::Bit5)
IO().triggerInterrupt(IoRegisters::Interrupts::DisplayControlStatus);
count += CPU().run(80); // ~19us
// Mode 3, OAM/VRAM unavailable
IO().updateLcdStatusMode(IoRegisters::LcdStatusMode::TransferringDataToLcd);
count += CPU().run(170); // ~41us
// Mode 0
IO().updateLcdStatusMode(IoRegisters::LcdStatusMode::HBlank);
if (IO().peek(IoRegisters::STAT) & Processor::Bit3)
IO().triggerInterrupt(IoRegisters::Interrupts::DisplayControlStatus);
count += CPU().run(limit - count); // ~48.6us
IO().incrementLY();
} else {
count += CPU().run(CyclesPerLine);
}
return count;
}
int EightBit::GameBoy::Bus::runVerticalBlankLines() {
const auto lines = TotalLineCount - Display::RasterHeight;
return runVerticalBlankLines(lines);
}
int EightBit::GameBoy::Bus::runVerticalBlankLines(int lines) {
/*
Vertical Blank interrupt is triggered when the LCD
controller enters the VBL screen mode (mode 1, LY=144).
This happens once per frame, so this interrupt is
triggered 59.7 times per second. During this period the
VRAM and OAM can be accessed freely, so it's the best
time to update graphics (for example, use the OAM DMA to
update sprites for next frame, or update tiles to make
animations).
This period lasts 4560 clocks in normal speed mode and
9120 clocks in double speed mode. That's exactly the
time needed to draw 10 scanlines.
The VBL interrupt isn't triggered when the LCD is
powered off or on, even when it was on VBL mode.
It's only triggered when the VBL period starts.
*/
if (m_enabledLCD) {
IO().updateLcdStatusMode(IoRegisters::LcdStatusMode::VBlank);
if (IO().peek(IoRegisters::STAT) & Processor::Bit4)
IO().triggerInterrupt(IoRegisters::Interrupts::DisplayControlStatus);
IO().triggerInterrupt(IoRegisters::Interrupts::VerticalBlank);
}
return runRasterLines(lines);
}