Stuffing the return stack buffer

Holy mackerel! There is nothing new under the sun!

Waaaay back when, late 1970s, I worked on Datapoint 2200/5500/6600 8 bit computers, Datapoint's extension of the basic 8008 into Z80 level, but different: no IX IY regs, had system/user modes, other differences.

It also had a 16 level hardware stack with no overflow or underflow detection or warning.

Its only interrupt was every millisecond whether you wanted it or not. Everything was polled.

We threw in a push, push, pop, pop, to force always using 3 levels of stack, because none of our interrupt code was supposed to use more than two levels, and user code was expected to never use more than 13 levels.

Deja vu all over again!