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First stage refactoring CPU instruction execution (to hopefully allow display interrupt interleave)

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Signed-off-by: Adrian Conlon <Adrian.conlon@gmail.com>
This commit is contained in:
Adrian Conlon 2017-09-30 15:28:25 +01:00
parent da438ffb85
commit 66b870bb78
2 changed files with 72 additions and 5 deletions
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1
LR35902/inc/LR35902.h
View File

@ -54,6 +54,7 @@ namespace EightBit {
private:
Bus& m_bus;
bool m_enabledLCD;
register16_t af;
register16_t bc;

76
LR35902/src/LR35902.cpp
View File

@ -8,6 +8,7 @@
EightBit::GameBoy::LR35902::LR35902(Bus& memory)
: IntelProcessor(memory),
m_bus(memory),
m_enabledLCD(false),
m_ime(false),
m_stopped(false),
m_prefixCB(false) {
@ -324,6 +325,7 @@ void EightBit::GameBoy::LR35902::ccf(uint8_t& a, uint8_t& f) {
#pragma region Controlled instruction execution
int EightBit::GameBoy::LR35902::runRasterLines() {
m_enabledLCD = !!(m_bus.peekRegister(Bus::LCDC) & Bus::LcdEnable);
m_bus.resetLY();
return runRasterLines(Display::RasterHeight * Bus::CyclesPerLine, Display::RasterHeight);
}
@ -341,13 +343,57 @@ int EightBit::GameBoy::LR35902::runRasterLines(int limit, int lines) {
}
int EightBit::GameBoy::LR35902::runRasterLine(int limit) {
const auto count = run(limit);
if (m_bus.peekRegister(Bus::LCDC) & Bus::LcdEnable) {
m_bus.updateLcdStatusMode(Bus::LcdStatusMode::HBlank);
m_bus.incrementLY();
/*
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 = Bus::CyclesPerLine;
if (m_enabledLCD) {
if ((m_bus.peekRegister(Bus::STAT) & Bit6) && (m_bus.peekRegister(Bus::LYC) == m_bus.peekRegister(Bus::LY)))
m_bus.triggerInterrupt(Bus::Interrupts::DisplayControlStatus);
m_bus.updateLcdStatusMode(Bus::LcdStatusMode::SearchingOamRam);
if (m_bus.peekRegister(Bus::STAT) & Bit5)
m_bus.triggerInterrupt(Bus::Interrupts::DisplayControlStatus);
count -= run(80); // ~19us
m_bus.updateLcdStatusMode(Bus::LcdStatusMode::TransferringDataToLcd);
count -= run(170); // ~41us
m_bus.updateLcdStatusMode(Bus::LcdStatusMode::HBlank);
if (m_bus.peekRegister(Bus::STAT) & Bit3)
m_bus.triggerInterrupt(Bus::Interrupts::DisplayControlStatus);
count -= run(203); // ~48.6us
m_bus.incrementLY();
} else {
count += run(Bus::CyclesPerLine);
}
assert(count == Bus::CyclesPerLine);
return count;
}
@ -357,8 +403,28 @@ int EightBit::GameBoy::LR35902::runVerticalBlankLines() {
}
int EightBit::GameBoy::LR35902::runVerticalBlankLines(int limit, int lines) {
if (m_bus.peekRegister(Bus::LCDC) & Bus::LcdEnable) {
/*
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) {
m_bus.updateLcdStatusMode(Bus::LcdStatusMode::VBlank);
if (m_bus.peekRegister(Bus::STAT) & Bit4)
m_bus.triggerInterrupt(Bus::Interrupts::DisplayControlStatus);
m_bus.triggerInterrupt(Bus::Interrupts::VerticalBlank);
}
return runRasterLines(limit, lines);