Firmware for a Sinner Cypreus Tri-EDC with a BLF17DD driver with 
triple XP-L emitters and a capacitor to enable off-time memory.

Interface:

  - A short press (0.5s or less) moves the mode forward by one.
  - A medium press (~0.5s to 1.5s) moves the mode backward by one.
  - A long press (more than 1.5s) resets to the first mode.  So, after 
    being off for a while it always starts at the first mode.
  - Going "backward" from the first mode will take you to semi-hidden 
    "negative" modes.
  - A short press from any "negative" mode resets the light to the first 
    mode.

Modes:

   1. Moon.  VERY voltage-sensitive, so it will be fairly bright on a 
      full cell and very dim on a low battery.  Sorry, the alternative 
      was to always be too bright to be considered a "moon" mode.
      (varies from ~0.01 lm to ~3.3 lm)
   2. Low / ~0.4% / ~12lm.
   3. Medium / ~3.1% / ~94lm.
   4. High / ~16.5% / ~494lm.
   5. Higher / ~47% / ~1411lm. (w/ turbo step-down to "high" after 30s)
   6. Maximum / 100% / ~3000lm. (w/ turbo step-down to "higher" after 30s)
   7. High-vis dual-level 1Hz flasher: Moon-Med.  Stutters at Med mode 
      briefly, then settles at Moon mode.  Repeats once per second.
   8. High-vis flasher: Low-High.
   9. High-vis flasher: Med-Higher.
  10. 1Hz Heartbeat beacon.  Blinks twice, waits, repeats.
  11. 12Hz motion-freezing strobe.  (not tactical, more like a party strobe)
  12. 24Hz motion-freezing strobe.
  13. 60Hz motion-freezing strobe.
  14. Self-ramping 10Hz to 24Hz motion-freezing strobe.  Point it at a 
      ceiling fan or something, it looks neat.
  15. Battery check mode.  Measures, blinks 0 to 5 times, waits, repeats:
      - 0 blinks: < 3.0V
      - 1 blink : 3.0-3.3V
      - 2 blinks: 3.3-3.6V
      - 3 blinks: 3.6-3.9V
      - 4 blinks: 3.9-4.2V
      - 5 blinks: > 4.2V

Negative modes:

  -1. "Impress" mode (a.k.a. maximum output),
      for quick access to "ZOMG that's bright!".
  -2. 24Hz strobe, looks nice on falling water.
  -3. Battery check mode.

When the battery voltage gets low, the light will step down and 
eventually turn off.  If on a blinky mode, it'll "step down" to the 
"Med" mode first, then low, then off.  If on a regular/solid mode, it 
will step down one level each time until it's at "low", then turn off.  
At low voltage, "moon" is basically the same as off, so we skip it 
during low-voltage step-down.

Lumen outputs above "medium" are estimated, not actually measured.  My 
light box has difficulties with this light for some reason.

The moon mode can use self-adjusting PFM to keep its brightness level 
more consistent, but it takes a lot of space in the code and the results 
are still mediocre.  However, it does at least look cool when it does 
the initial adjustment (ramps up, looks best on a battery near 3.7V).