Re:A first look at WebAssembly performance
by flohofwoe on Thursday February 09, 2017 @10:25AM
(#13607525)
He, do it better then ;) The CPU emulation alone is about 300x faster then an original Z80 (runs at 1.2 GHz on the same MBP), most performance is currently burned in the CPC video emulation (way more expensive then the CPU). The CPU and memory system is quite optimized, the other systems not so much.
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Re:A first look at WebAssembly performance
by rasz_pl on Thursday February 09, 2017 @12:50PM
(#13609034)
afaik CPC video is very basic, pretty much a raw MC6845 crtc. No sprites, no blitters, no dma. What is giving you so much problems performance wise?
Re:A first look at WebAssembly performance
by flohofwoe on Thursday February 09, 2017 @01:17PM
(#13609326)
The video config can be changed by the CPU in the middle of a scanline so you can't decode an entire scanline in a tight loop but need to run video decoding interleaved with the CPU (currently it's ticked after an entire CPU instruction though, not per cycle), and every tick of the video system needs to figure out all the decoding parameters again, because they might have changed since the last tick (and demo-scene demos use this mid-scanline-stuff a lot).
Also the display isn't driven directly by the 6845, HSYNC and VSYNC go through the Gate Array where a few ticks of latency is added, the same is true for the interrupt request that happens every 52 scanlines.
On top of that the CPC has an extra funky pixel bit pattern (http://cpctech.cpc-live.com/docs/graphics.html)
I haven't spent any time at all yet optimizing the video system though, for instance the pixel decoding might benefit from lookup tables. I first want to get it accurate enough for demo-scene gfx demos, and than will take care of performance.