FA-81577 / MIDI event timing / Member archive

MIDI clock transport and song position: song position LSB and MSB swapped · case 02

A pointer of 4 sixteenths (lsb 4, msb 0) locates to sixteenth 512 instead of 4.

Member previewVariant 2 · 3 implementations · 8 checks per implementation

Case contract

Input a list of messages: ["start"], ["continue"], ["stop"], ["clock"] or ["spp", lsb, msb]. start resets the position to 0 and runs; continue runs from the current position; stop halts; clock advances the position by one clock only while running; a song position pointer (in sixteenth notes, 6 clocks each, 14-bit lsb/msb) is honoured only while stopped. Return [position in clocks, running, quarter notes = position // 24]; unknown messages return None.

Why this case matters

MIDI sequencers, file readers and synth drivers depend on exact event ordering and tick/time arithmetic.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
oracle 0	`[6, true, 0]`	`[768, true, 32]`	Failed

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