Fix #2: Add strobe mode

If users want a strobe mode, they usually want it for defence purposes.
Thus it should be possible to enter it as fast as possible. If strobe is
enabled (first option if STROBE is compiled) the flashlight always
starts in a strobe mode. Then a single press of the power switch enters
the usual UI.

rampinglight.c

@@ -18,6 +18,7 @@
 // Optional features
 #define BATTCHECK
 #define BEACON
+#define STROBE
 #define LOW_VOLTAGE_PROTECTION
 
 #include <avr/io.h>
@@ -84,6 +85,9 @@ enum State {
 #ifdef BEACON
   kBeacon,
 #endif  // ifdef BEACON
+#ifdef STROBE
+  kStrobe,
+#endif  // ifdef STROBE
 };
 
 /**
@@ -96,6 +100,7 @@ typedef union {
     unsigned mode_memory : 1;
     unsigned freeze_on_high : 1;
     unsigned start_high : 1;
+    unsigned strobe : 1;
   };
 } Options;
 
@@ -389,7 +394,11 @@ int main(void) {
   }
 
   if (coldboot) {  // Initialize state after the flashlight was switched off for some time
+#ifdef STROBE
+    state = options.strobe ? kStrobe : kDefault;
+#else
     state = kDefault;
+#endif  // ifdef STROBE
     fast_presses = 0;
     ramping_up = 1;
 
@@ -540,6 +549,14 @@ int main(void) {
         break;
 #endif  // ifdef BEACON
 
+#ifdef STROBE
+      case kStrobe:
+        set_pwm(TURBO_PWM);
+        blink(8,2);
+        blink(8,4);
+        break;
+#endif  // ifdef STROBE
+
       case kConfig:
         disable_output();
         set_pwm(FLASH_PWM);
@@ -548,10 +565,14 @@ int main(void) {
         state = kDefault;  // Exit config mode after one iteration
 
         // This assumes that the bit field starts at the least significant bit
-        toggle_option(options.raw ^ 0b00000001, 1);  // Fixed mode
-        toggle_option(options.raw ^ 0b00000010, 2);  // Mode memory
-        toggle_option(options.raw ^ 0b00000100, 3);  // Freeze on high
-        toggle_option(options.raw ^ 0b00001000, 4);  // Start with high
+        uint8_t flashes = 1;  // Removed by compile time calculation
+#ifdef STROBE
+        toggle_option(options.raw ^ 0b00010000, flashes++);  // Start with strobe
+#endif  // ifdef STROBE
+        toggle_option(options.raw ^ 0b00000001, flashes++);  // Fixed mode
+        toggle_option(options.raw ^ 0b00000010, flashes++);  // Mode memory
+        toggle_option(options.raw ^ 0b00000100, flashes++);  // Freeze on high
+        toggle_option(options.raw ^ 0b00001000, flashes++);  // Start with high
 
         set_level(output);  // Restore previous level