kevin@sun.uucp (Kevin Sheehan) (02/18/86)
HP's 2100/21mx/1000/whatever they are called this year had the same feature - the sign bit on a 16-bit pointer caused indirection to continue. As the pointers were to words, it left you talking to 32KW (W = 16bits) as most, except for the (later) kludged in character pointers which pointed to bytes, and therefore didnt use the indirect bit (and werent the same address either - my first lesson with (int *) != (char *)) It also had the same "feature" about pointers to each other, it would hang the system, dead even to interrupts. When HP finally let you talk to more memory, some of the games to get to it resembled certain unnatural acts... Two other things stand out about this family in my memory, they let you talk to the registers as memory locations, so absolute addressing would also let you talk to a register. In C, you could declare something in a register, and later take its address (but why bother with only 2 registers :-) The other pleasant feature was the way you called a subroutine: jsr blarp blarp: nop <--- return address goes here, no stack When you jsr, it writes the return location there, then continues on after that. No I/D protection here fans, you couldnt ROM anything that did jsr's, and you couldnt do recursive/reentrant code without resorting to previously mentioned deviant activies (and some real fast talking to the atom gods) On the other hand, the suckers never broke, and the family is still a pretty good workhorse for a machine that was old when I was in high school. l & h, kev Disclaimer: if they cant take a joke...