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In addition to this, Jörn convinced me that pre-emptive multitasking was possible on the 6502, so in May 2014, I began the arduous task of converting the existi
by dsp1234 11y ago
In addition to this, Jörn convinced me that pre-emptive multitasking was possible on the 6502, so in May 2014, I began the arduous task of converting the existing code to run from a bank-switched cartridge, while simultaneously designing the pre-emptively multitasking kernel.
What is especially heartening at this stage is that the 8-bit Atari can actually run a pre-emptive scheduler, and run it well – in spite of the 6502’s fixed stack.
Looks like it is.
- alain94040 11y agoIn 1987 I published a preemptive multitasking for 6502[1] (Apple II). If I remember properly (it's only been 30 years or so), the stack is fixed at $100, so all you need to do on a context switch is save the stack somewhere else and restore it. That's 256 bytes to move around. I used the mouse card as an interrupt source (video refresh) to get a regular source of interrupts. [1] I can't find any trace online, except for some weird Word document of what must have been the original README file.