FA-89133 / Digital logic simulation / Member archive

Out-of-range read returns zero · case 03

Reading past the end of the memory yields 0 instead of 'x'.

Member previewVariant 3 · 3 implementations · 7 checks per implementation

Case contract

Input [depth, mode, ops]; memory holds 16-bit words initialised to 0. Each op [we, addr, wdata, be, re]: be bit k enables byte lane k (bits 8k..8k+7). Addresses outside 0..depth-1 ignore writes and read 'x'. A read in the same cycle as a write returns the old word in mode 'read_first' and the merged new word in 'write_first'. re=0 yields None.

Why this case matters

RTL memory models must match the inferred RAM read-during-write and byte-enable behaviour or simulation diverges from silicon.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
negative address rejected	`[0, 0]`	`["x", 0]`	Failed

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