FA-89409 / Instruction set emulation / Member archive

Stack pointer sticks at zero · case 04

Pushing past the bottom of the stack page overwrites the same byte repeatedly.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

Input [pc, sp, ops] for an 8-bit stack pointer addressing page 0x100. push stores at 0x100+sp then decrements sp (wrapping in 8 bits); pull increments sp (wrapping) then reads (unwritten bytes read 0). jsr t (3 bytes at pc) pushes (pc+2) high byte then low byte and jumps; rts pulls low then high and resumes at that address + 1 (16-bit wrap). pha v pushes v, pla pulls; both and nop advance pc by 1. Return [[pc, sp, pulled value or None] per op, sorted [address, byte] of written stack memory].

Why this case matters

Emulated call/return must reproduce the exact stack image because programs inspect and manipulate return addresses on the stack.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
stack pointer wraps below page start	`[[[769, 0, null], [770, 0, null], [771, 0, null], [772, 1, 51]], [[256, 89], [257, 51]]]`	`[[[769, 0, null], [770, 255, null], [771, 254, null], [772, 255, 89]], [[256, 68], [257, 51], [511, 89]]]`	Failed

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