mirror of https://github.com/bsnes-emu/bsnes.git
83 lines
3.1 KiB
C++
83 lines
3.1 KiB
C++
auto CPU::bus_idle() -> void {
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prefetch_step(1);
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}
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auto CPU::bus_read(unsigned mode, uint32 addr) -> uint32 {
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addr &= 0x0fff'ffff;
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unsigned wait = bus_wait(mode, addr);
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unsigned word = pipeline.fetch.instruction;
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if(addr & 0x0800'0000) {
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if(mode & Prefetch && regs.wait.control.prefetch) {
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prefetch_sync(addr);
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word = prefetch_read();
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if(mode & Word) word |= prefetch_read() << 16;
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} else {
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if(!active.dma) prefetch_wait();
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step(wait - 1);
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word = addr < 0x0e00'0000 ? cartridge.rom_read(mode, addr) : cartridge.ram_read(mode, addr);
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step(1);
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}
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} else {
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prefetch_step(wait - 1);
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if(addr < 0x0200'0000) word = bios.read(mode, addr);
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else if(addr < 0x0300'0000) word = ewram_read(mode, addr);
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else if(addr < 0x0400'0000) word = iwram_read(mode, addr);
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else if(addr >= 0x0700'0000) word = ppu.oam_read(mode, addr);
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else if(addr >= 0x0600'0000) word = ppu.vram_read(mode, addr);
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else if(addr >= 0x0500'0000) word = ppu.pram_read(mode, addr);
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else if((addr & 0xffff'fc00) == 0x0400'0000) word = bus.mmio[addr & 0x3ff]->read(mode, addr);
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else if((addr & 0xff00'ffff) == 0x0400'0800) word = ((MMIO*)this)->read(mode, 0x0400'0800 | (addr & 3));
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prefetch_step(1);
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}
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return word;
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}
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auto CPU::bus_write(unsigned mode, uint32 addr, uint32 word) -> void {
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addr &= 0x0fff'ffff;
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unsigned wait = bus_wait(mode, addr);
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if(addr & 0x0800'0000) {
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if(!active.dma) prefetch_wait();
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step(wait);
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addr < 0x0e00'0000 ? cartridge.rom_write(mode, addr, word) : cartridge.ram_write(mode, addr, word);
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} else {
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prefetch_step(wait);
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if(addr < 0x0200'0000);
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else if(addr < 0x0300'0000) ewram_write(mode, addr, word);
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else if(addr < 0x0400'0000) iwram_write(mode, addr, word);
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else if(addr >= 0x0700'0000) ppu.oam_write(mode, addr, word);
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else if(addr >= 0x0600'0000) ppu.vram_write(mode, addr, word);
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else if(addr >= 0x0500'0000) ppu.pram_write(mode, addr, word);
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else if((addr & 0xffff'fc00) == 0x0400'0000) bus.mmio[addr & 0x3ff]->write(mode, addr, word);
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else if((addr & 0xff00'ffff) == 0x0400'0800) ((MMIO*)this)->write(mode, 0x0400'0800 | (addr & 3), word);
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}
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}
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auto CPU::bus_wait(unsigned mode, uint32 addr) -> unsigned {
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if(addr < 0x0200'0000) return 1;
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if(addr < 0x0300'0000) return (16 - regs.memory.control.ewramwait) * (mode & Word ? 2 : 1);
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if(addr < 0x0500'0000) return 1;
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if(addr < 0x0700'0000) return mode & Word ? 2 : 1;
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if(addr < 0x0800'0000) return 1;
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static unsigned timings[] = {5, 4, 3, 9};
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unsigned n = timings[regs.wait.control.nwait[addr >> 25 & 3]];
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unsigned s = regs.wait.control.swait[addr >> 25 & 3];
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switch(addr & 0x0e00'0000) {
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case 0x0800'0000: s = s ? 2 : 3; break;
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case 0x0a00'0000: s = s ? 2 : 5; break;
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case 0x0c00'0000: s = s ? 2 : 9; break;
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case 0x0e00'0000: s = n; break;
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}
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bool sequential = (mode & Sequential);
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if((addr & 0x1fffe) == 0) sequential = false; //N cycle on 16-bit ROM crossing 128KB page boundary (RAM S==N)
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unsigned clocks = sequential ? s : n;
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if(mode & Word) clocks += s; //16-bit bus requires two transfers for words
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return clocks;
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}
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