arduino_gauge_controller/changes.md

Changes

2026-04-27 — Arduino firmware refactor (Gaugecontroller/Gaugecontroller.ino)

Non-blocking VFD multiplexer

vfd::refresh() previously held each digit for 2000 µs via delayMicroseconds, which capped the effective stepper pulse rate at roughly 500 Hz regardless of maxSpeed. It now tracks phaseStartMicros/phaseActive and returns immediately while the digit is still being held; the main loop runs at microsecond cadence again and the configured maxSpeed = 4000.0f steps/s is actually achievable.

Fixed-buffer command parser (no more String heap churn)

Replaced String rxLine with char rxBuf[128] and converted the entire command pipeline to take const char*:

• processLine, sendReply, vfd::parseCommand
• All parse* functions: parseSet, parseSpeed, parseAccel, parseEnable, parseZero, parseHome, parseSweep, parsePosQuery, parseCfgQuery, parseLedQuery, parseLed, parseBlink, parseBreathe, parseDflash, parseVfd, parsePing.

parseSpeed / parseAccel / parseSweep use strncmp + atof because the default AVR-libc sscanf doesn't support %f. No allocations on the command path; the Mega's heap no longer fragments over time.

Cached ledNeedsSwap[TOTAL_LEDS]

Per-LED RGB-vs-GRB swap flag is now precomputed once in setup() from gaugePins[].ledOrder. encodeForStrip is a single array index instead of walking the gauge table on every LED read/write.

Cached step direction per gauge

Added Gauge.lastDir. setDir() skips the DIR-pin digitalWrite when the direction hasn't flipped (the common case during a step run) and adds a 1 µs DIR-to-STEP setup delay only when it actually flips.

Cleanups

• Removed the absf helper; use fabsf consistently.
• Removed the + 0.0001f epsilon in the trapezoidal braking-distance divisor. parseAccel already rejects accel <= 0, so the divisor is always positive.
• Fixed the <r> <ig> <b> typo to <r> <g> <b> in the protocol comment for DFLASH.

Build verification

arduino-cli compile --fqbn arduino:avr:mega Gaugecontroller: 17758 B flash (6%), 1845 B SRAM (22%).