RTL Design #3 · 2026-09-26 · Waveform debug · Hard · about 15 min

A depth-4 FIFO that counts to 5

The waveform comes from this synchronous FIFO with DEPTH = 4. Seven writes are attempted back to back, then five reads. At the marker, count reaches 5: the FIFO accepted a write it had no room for.

Find the cause in the waveform, then fix fifo.sv. full and empty must match what the FIFO holds on every cycle: a write is accepted only while full is 0, and a read only while empty is 0, even when both happen in the same cycle.

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