🚀 go-pugleaf

+---------------
| I've been playing around with sumacc C programming and had to do a little
| programming in assembly language to handle some special cases.  I've
| noticed that the high byte of an address (the 68000 only uses the bottom
| 24 bits) is used alot in the Mac for special purposes.  However, even when
| I do a Load Effective Address (lea) command, the high byte is sometimes
| non-zero and I have to clear it out.  Does anyone know if the hardware in
| the Mac uses that high byte for something?
| Edward Moy | edmoy@ucbopal | ucbvax!ucbopal!edmoy
+---------------

<Anguished Flame>
NO, NO! SAY IT ISN'T SO! If they have done this, it's going to be a major
disaster when they go to a 68020, where those bits are significant. Don't
we learn ANYTHING from our mistakes in this industry? Wasn't it enough that
all those 360 programs had to be re-written for 370s???????? I don't expect
the front line troops to remember (they're too young in many cases), but
doesn't Management ever come to design reviews? Using "spare" bits for
cutesy tags is simply too dangerous to consider (unless the usage is tightly
confined to a few SMALL modules you plan on replacing in the next generation).

((...and even then, clever users will discover them, use them, and be greatly
upset when you take them away...))


Rob Warnock
Systems Architecture Consultant

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