mirror of https://github.com/bsnes-emu/bsnes.git
c50723ef61
byuu wrote: Aforementioned scheduler changes added. Longer explanation of why here: http://hastebin.com/raw/toxedenece Again, we really need to test this as thoroughly as possible for regressions :/ This is a really major change that affects absolutely everything: all emulation cores, all coprocessors, etc. Also added ADDX and SUB to the 68K core, which brings us just barely above 50% of the instruction encoding space completed. [Editor's note: The "aformentioned scheduler changes" were described in a previous forum post: Unfortunately, 64-bits just wasn't enough precision (we were getting misalignments ~230 times a second on 21/24MHz clocks), so I had to move to 128-bit counters. This of course doesn't exist on 32-bit architectures (and probably not on all 64-bit ones either), so for now ... higan's only going to compile on 64-bit machines until we figure something out. Maybe we offer a "lower precision" fallback for machines that lack uint128_t or something. Using the booth algorithm would be way too slow. Anyway, the precision is now 2^-96, which is roughly 10^-29. That puts us far beyond the yoctosecond. Suck it, MAME :P I'm jokingly referring to it as the byuusecond. The other 32-bits of precision allows a 1Hz clock to run up to one full second before all clocks need to be normalized to prevent overflow. I fixed a serious wobbling issue where I was using clock > other.clock for synchronization instead of clock >= other.clock; and also another aliasing issue when two threads share a common frequency, but don't run in lock-step. The latter I don't even fully understand, but I did observe it in testing. nall/serialization.hpp has been extended to support 128-bit integers, but without explicitly naming them (yay generic code), so nall will still compile on 32-bit platforms for all other applications. Speed is basically a wash now. FC's a bit slower, SFC's a bit faster. The "longer explanation" in the linked hastebin is: Okay, so the idea is that we can have an arbitrary number of oscillators. Take the SNES: - CPU/PPU clock = 21477272.727272hz - SMP/DSP clock = 24576000hz - Cartridge DSP1 clock = 8000000hz - Cartridge MSU1 clock = 44100hz - Controller Port 1 modem controller clock = 57600hz - Controller Port 2 barcode battler clock = 115200hz - Expansion Port exercise bike clock = 192000hz Is this a pathological case? Of course it is, but it's possible. The first four do exist in the wild already: see Rockman X2 MSU1 patch. Manifest files with higan let you specify any frequency you want for any component. The old trick higan used was to hold an int64 counter for each thread:thread synchronization, and adjust it like so: - if thread A steps X clocks; then clock += X * threadB.frequency - if clock >= 0; switch to threadB - if thread B steps X clocks; then clock -= X * threadA.frequency - if clock < 0; switch to threadA But there are also system configurations where one processor has to synchronize with more than one other processor. Take the Genesis: - the 68K has to sync with the Z80 and PSG and YM2612 and VDP - the Z80 has to sync with the 68K and PSG and YM2612 - the PSG has to sync with the 68K and Z80 and YM2612 Now I could do this by having an int64 clock value for every association. But these clock values would have to be outside the individual Thread class objects, and we would have to update every relationship's clock value. So the 68K would have to update the Z80, PSG, YM2612 and VDP clocks. That's four expensive 64-bit multiply-adds per clock step event instead of one. As such, we have to account for both possibilities. The only way to do this is with a single time base. We do this like so: - setup: scalar = timeBase / frequency - step: clock += scalar * clocks Once per second, we look at every thread, find the smallest clock value. Then subtract that value from all threads. This prevents the clock counters from overflowing. Unfortunately, these oscillator values are psychotic, unpredictable, and often times repeating fractions. Even with a timeBase of 1,000,000,000,000,000,000 (one attosecond); we get rounding errors every ~16,300 synchronizations. Specifically, this happens with a CPU running at 21477273hz (rounded) and SMP running at 24576000hz. That may be good enough for most emulators, but ... you know how I am. Plus, even at the attosecond level, we're really pushing against the limits of 64-bit integers. Given the reciprocal inverse, a frequency of 1Hz (which does exist in higan!) would have a scalar that consumes 1/18th of the entire range of a uint64 on every single step. Yes, I could raise the frequency, and then step by that amount, I know. But I don't want to have weird gotchas like that in the scheduler core. Until I increase the accuracy to about 100 times greater than a yoctosecond, the rounding errors are too great. And since the only choice above 64-bit values is 128-bit values; we might as well use all the extra headroom. 2^-96 as a timebase gives me the ability to have both a 1Hz and 4GHz clock; and run them both for a full second; before an overflow event would occur. Another hastebin includes demonstration code: #include <libco/libco.h> #include <nall/nall.hpp> using namespace nall; // cothread_t mainThread = nullptr; const uint iterations = 100'000'000; const uint cpuFreq = 21477272.727272 + 0.5; const uint smpFreq = 24576000.000000 + 0.5; const uint cpuStep = 4; const uint smpStep = 5; // struct ThreadA { cothread_t handle = nullptr; uint64 frequency = 0; int64 clock = 0; auto create(auto (*entrypoint)() -> void, uint frequency) { this->handle = co_create(65536, entrypoint); this->frequency = frequency; this->clock = 0; } }; struct CPUA : ThreadA { static auto Enter() -> void; auto main() -> void; CPUA() { create(&CPUA::Enter, cpuFreq); } } cpuA; struct SMPA : ThreadA { static auto Enter() -> void; auto main() -> void; SMPA() { create(&SMPA::Enter, smpFreq); } } smpA; uint8 queueA[iterations]; uint offsetA; cothread_t resumeA = cpuA.handle; auto EnterA() -> void { offsetA = 0; co_switch(resumeA); } auto QueueA(uint value) -> void { queueA[offsetA++] = value; if(offsetA >= iterations) { resumeA = co_active(); co_switch(mainThread); } } auto CPUA::Enter() -> void { while(true) cpuA.main(); } auto CPUA::main() -> void { QueueA(1); smpA.clock -= cpuStep * smpA.frequency; if(smpA.clock < 0) co_switch(smpA.handle); } auto SMPA::Enter() -> void { while(true) smpA.main(); } auto SMPA::main() -> void { QueueA(2); smpA.clock += smpStep * cpuA.frequency; if(smpA.clock >= 0) co_switch(cpuA.handle); } // struct ThreadB { cothread_t handle = nullptr; uint128_t scalar = 0; uint128_t clock = 0; auto print128(uint128_t value) { string s; while(value) { s.append((char)('0' + value % 10)); value /= 10; } s.reverse(); print(s, "\n"); } //femtosecond (10^15) = 16306 //attosecond (10^18) = 688838 //zeptosecond (10^21) = 13712691 //yoctosecond (10^24) = 13712691 (hitting a dead-end on a rounding error causing a wobble) //byuusecond? ( 2^96) = (perfect? 79,228 times more precise than a yoctosecond) auto create(auto (*entrypoint)() -> void, uint128_t frequency) { this->handle = co_create(65536, entrypoint); uint128_t unitOfTime = 1; //for(uint n : range(29)) unitOfTime *= 10; unitOfTime <<= 96; //2^96 time units ... this->scalar = unitOfTime / frequency; print128(this->scalar); this->clock = 0; } auto step(uint128_t clocks) -> void { clock += clocks * scalar; } auto synchronize(ThreadB& thread) -> void { if(clock >= thread.clock) co_switch(thread.handle); } }; struct CPUB : ThreadB { static auto Enter() -> void; auto main() -> void; CPUB() { create(&CPUB::Enter, cpuFreq); } } cpuB; struct SMPB : ThreadB { static auto Enter() -> void; auto main() -> void; SMPB() { create(&SMPB::Enter, smpFreq); clock = 1; } } smpB; auto correct() -> void { auto minimum = min(cpuB.clock, smpB.clock); cpuB.clock -= minimum; smpB.clock -= minimum; } uint8 queueB[iterations]; uint offsetB; cothread_t resumeB = cpuB.handle; auto EnterB() -> void { correct(); offsetB = 0; co_switch(resumeB); } auto QueueB(uint value) -> void { queueB[offsetB++] = value; if(offsetB >= iterations) { resumeB = co_active(); co_switch(mainThread); } } auto CPUB::Enter() -> void { while(true) cpuB.main(); } auto CPUB::main() -> void { QueueB(1); step(cpuStep); synchronize(smpB); } auto SMPB::Enter() -> void { while(true) smpB.main(); } auto SMPB::main() -> void { QueueB(2); step(smpStep); synchronize(cpuB); } // #include <nall/main.hpp> auto nall::main(string_vector) -> void { mainThread = co_active(); uint masterCounter = 0; while(true) { print(masterCounter++, " ...\n"); auto A = clock(); EnterA(); auto B = clock(); print((double)(B - A) / CLOCKS_PER_SEC, "s\n"); auto C = clock(); EnterB(); auto D = clock(); print((double)(D - C) / CLOCKS_PER_SEC, "s\n"); for(uint n : range(iterations)) { if(queueA[n] != queueB[n]) return print("fail at ", n, "\n"); } } } ...and that's everything.] |
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| .. | ||
| cartridge | ||
| controller | ||
| coprocessor | ||
| cpu | ||
| dsp | ||
| expansion | ||
| interface | ||
| memory | ||
| ppu | ||
| slot | ||
| smp | ||
| system | ||
| GNUmakefile | ||
| debugger.hpp | ||
| sfc.hpp | ||