# 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%).