eFuelPro

A fuel forecourt runs on trust and a clipboard. The dispenser knows exactly what it dispensed; the owner finds out later, from a total that has been through several hands. There is no dispute to resolve because there is no record to dispute.

The ask was simple to state: print a receipt for every sale, keep a ledger the owner can read from anywhere, and make loyalty work without a card reader that people forget to use.

The dispenser had a serial port and no documentation for it. Everything else followed from that.

The bus is shared with legacy equipment, so a clean frame is the lucky case rather than the normal one. The C++ framing layer validates delimiters and device prefixes and resynchronises byte by byte through corruption — recovering cleanly where fixed-offset parsing had been silently returning garbage that looked like data.

One failure took real hunting: a 0x88 bus-clearing broadcast from another device that was quietly corrupting calibration.

Then the per-site problem. Every forecourt wires its dispenser slightly differently, and hand-configuring each install does not scale. So the device works its own mapping out: it samples a stable idle baseline across 15 frames, detects the start signal, and scores every candidate byte permutation against BCD validity, monotonicity and the measured price-per-unit — taking the lowest-error mapping inside a 1% tolerance. The map self-expands at runtime as more digits activate. Per-site manual setup was removed entirely.