JAMES FRIEND MAC EMULATOR UPDATE
Ideally we could yield back to the browser after every single cycle of the CPU, so that we could collect the latest inputs from the mouse and keyboard, and update the screen if necessary. Emscripten calls this callback many times a second.
The emulator initializes normally, and then instead of running the emulated system in an infinite loop, it registers a callback function with the Emscripten runtime which, when called, will run a bunch clock cycles of the emulated computer's CPU. The way I modified the existing code to achieve this sort of chunked execution was pretty blunt, but it worked.
JAMES FRIEND MAC EMULATOR MAC OS
You could draw a comparison between this and a 'cooperative multitasking' operating system, such as Classic Mac OS itself. So I had to break the control flow of the emulator code up, so that it could perform a 'chunk' of work emulating the Macintosh CPU and other hardware, and then allow the browser to do it's thing before the next chunk of work. However, Javascript code running in a web browser can't just run indefinitely, it must regularly yield control back to the browser so that I/O can be performed (updating the screen, triggering mouse and keyboard event handlers, etc). The program doesn't need to know when this will happen or do anything special to enable it. The program can rely on the operating system to manage the program's usage of the CPU, interrupting it periodically so that other programs can do some work.
In modern operating systems, native programs can run as one unbroken thread of execution. Once the code compiled successfully and was able to start up in the browser without crashing, the next issue to deal with was 'yielding' to the browser event loop. Emscripten also handles the mapping of native APIs to browser equivalents, so SDL rendering calls become Canvas API calls, browser input events become SDL events, etc. Emscripten's wrapper for Autotools' configure, called emconfigure, does most of the work here. This involved adjusting the project's GNU Autotools-based build system to use Emscripten's emcc compiler executable instead of gcc. As I did the initial work of porting this emulator to the browser (back in 2013), I thought it would be worthwhile to provide a run-down of the tools and hacks which made this possible.įirst, I had to get the emulator's C codebase to compile to ASM.js-compatible Javascript using Emscripten. When you start up the emulated computer on these pages of the Internet Archive, you're running the PCE emulator, originally a piece of software intended to run natively on desktop operating systems, which has been adapted and recompiled to run in your web browser. This is great because it provides the same level of accessibility and convenience to emulation as you'd expect of playing a media file or viewing a document.
JAMES FRIEND MAC EMULATOR ARCHIVE
The Internet Archive recently added the original Macintosh to the list of classic computers of which they provide emulation, so you can run their archive of software titles in your browser, without installing anything.
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