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5

You can actually generate a "spurious interrupt" condition on the Atari ST with its MFP (68901) - Not on purpose, but rather because of a glitch in the Motorola 68901 - If you disable interrupts on the MFP exactly at the point when the CPU starts an IACK cycle (i.e with the last instructions before the /INT), it will not provide a vector, the CPU ...


0

The original Mac used BERR for the "Programmers Switch", which was a small switch that could be installed (well, the switch was always there, but access to the switch could be installed). The Programmers Switch had two buttons: the interrupt button, and the reset button. Reset is pretty obvious, the Interrupt button was designed to be patched in to ...


7

To save space and execution time (and partly of necessity, cf. below), interrupt handlers are typically set up for the context they are used in with assumptions on expected system interrupt sources. If you were to set up a context in which you might be receiving interrupts from both the VIC (maybe raster or sprite collision interrupt) and a CIA (maybe a ...


7

Based on my findings above, it seems that there is no need to identify the IRQ source in interrupt handlers, or at least it is not a regular practice. Why? Because there are no unknown/unexpected interrupts? The C64 is a rather simple machine, originally developed as a game console. Later usage is still much like one. C64 software assumes to be loaded as ...


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