• Screwtape's avatar
    Update to v103r07 release. · d4876a83
    Screwtape authored
    byuu says:
      - gba/cpu: massive code cleanup effort
      - gba/cpu: DMA can run in between active instructions¹
      - gba/cpu: added two-cycle startup delay between DMA activation and
        DMA transfers²
      - processor/spc700: BBC, BBC, CBNE cycle 4 is an idle cycle
      - processor/spc700: ADDW, SUBW, MOVW (read) cycle 4 is an idle cycle
    ¹: unfortunately, this causes yet another performance penalty for the
    poor GBA core =( Also, I think I may have missed disabling DMAs while
    the CPU is stopped. I'll fix that in the next WIP.
    ²: I put the waiting counter decrement at the wrong place, so this
    doesn't actually work. Needs to be more like
        auto CPU::step(uint clocks) -> void {
          for(auto _ : range(clocks)) {
            for(auto& timer : this->timer) timer.run();
            for(auto& dma : this->dma) if(dma.active && dma.waiting) dma.waiting--;
        auto CPU::DMA::run() -> bool {
          if(cpu.stopped() || !active || waiting) return false;
          if(irq) cpu.irq.flag |= CPU::Interrupt::DMA0 << id;
          if(drq && id == 3) cpu.irq.flag |= CPU::Interrupt::Cartridge;
          return true;
    Of course, the real fix will be restructuring how DMA works, so that
    it's always running in parallel with the CPU instead of this weird
    design where it tries to run all channels in some kind of loop until no
    channels are active anymore whenever one channel is activated.
    Not really sure how to design that yet, however.
instructions.cpp 12.3 KB