There are a number of 6502 JavaScript emulators out there will give you a pretty decent performance on a PC.

Recently I got eager to know what the performance would be of a JavaScript emulator on a mobile device like an Android or an iPhone.

Obviously on a mobile device you will not have as much horsepower as on a desktop pc.

Has anyone attempted to write a JavaScript emulator that runs smoothly on a mobile device?

Any thoughts/stories welcome.

Given that a typical modern mobile device (smartphone or tablet) has more than 2 times the performance of a Cray X-MP, I don't think that lack of horsepower should be a concern.

I think support for a touch interface might be the biggest problem.

There's a list of JavaScript emulators at
https://github.com/fcambus/jsemu#emulat ... javascript
many of which are 6502.

(I did run the visual6502 on a Kindle at one time...)

@rwiker: It seems that a native emulator like Frodo64 does run very smooth on a mobile device indeed. It does however seems that despite of recent improvements to JavaScript exceution in browsers, there is still a bit of an overhead. This overhead is not so noticeable when you run something like visual6502, as mentioned by BigEd. It is more noticeable when you play a game.

I did a test the other day on an core I7 pc. I first run Vice and looked at its cpu utilisation. It was constantly at 0%. I then fire up the C64 Javascript emulator I am developing in another post in Chrome. The Chrome task was utilising about 3% cpu. This might give an idea on what a mobile device might need to cope with.

@BigEd: Jip the touch screen is really a challenge. It is virtually impossible in Javascript to bring up the native system touch keyboard on demand. So, one is left to implement element responding to touchenter and touchleave events. It interesting, I haven't actually encountered any machine specific javascript emulator (e.g. C64 and so on) catering for a touch screen.

C1Pjs seems to do reasonably well at managing focus on the ipad. Possibly it does it using contenteditable:true??
http://www.pcjs.org/docs/c1pjs/

I would assume that sticking to asm.js would give you realtime speed on handheld browsers, but of course that's abandoning most of the JS concepts for a more C-like model.

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WFDis Interactive 6502 Disassembler
AcheronVM: A Reconfigurable 16-bit Virtual CPU for the 6502 Microprocessor