>PHP is most commonly used in interrupt routines (which the 2600 doesn't
>have, obviously) to save and restore the status of the CPU flags.
>
>Operating systems find it useful to use PHP to create universally useful
>procedures that don't mess with the CPU status any more than necessary.
Right, and Stella is essentially the "operating system" for the 2600, built
to take advantage of CPU tricks like that.
>Given COMBAT's twiddling of that port's unused bit (that I'm back to being
>sure is for a console LED), it's entirely possible they built the missile
>enable bit that way deliberately. The inner loops of COMBAT are sloppy
>speed-wise but very tight on code efficiency. Without many bytes to spare
>it was probably cheaper to do a last minute remask of the TIA than to
>sacrifice game features or add ROM.
Who said it was last minute? Might have been that way all along.. we don't
know =) Was Combat developed in conjunction with the hardware?
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