diff --git a/CMakeLists.txt b/CMakeLists.txt
index 53dc743..87ef223 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -30,4 +30,4 @@ add_custom_target(
         WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
 )
 
-add_executable(Z_DUMMY_TARGET ${SRC_LIST} src/mode/Test/Border.h src/mode/Clock/Clock.h src/mode/SpaceInvaders/SpaceInvaders.h)
+add_executable(Z_DUMMY_TARGET ${SRC_LIST} src/mode/Test/Border.h src/mode/Clock/Clock.h src/mode/SpaceInvaders/SpaceInvaders.h src/mode/Timer.h src/mode/Pong/Pong.cpp src/BASICS.cpp src/display/Display.cpp)
diff --git a/platformio.ini b/platformio.ini
index f046059..f8f6fcf 100644
--- a/platformio.ini
+++ b/platformio.ini
@@ -13,7 +13,9 @@ platform = espressif32
 board = esp32dev
 framework = arduino
 lib_deps = https://github.com/adafruit/Adafruit_NeoPixel
-upload_port = /dev/ttyUSB0
-upload_speed = 921600
+upload_port = 10.0.0.120
+upload_protocol = espota
+;upload_port = /dev/ttyUSB0
+;upload_speed = 921600
 monitor_port = /dev/ttyUSB0
 monitor_speed = 115200
diff --git a/src/BASICS.cpp b/src/BASICS.cpp
new file mode 100644
index 0000000..d87542d
--- /dev/null
+++ b/src/BASICS.cpp
@@ -0,0 +1,23 @@
+#include "BASICS.h"
+
+double step(double valueCurrent, double valueMin, double valueMax, microseconds_t timeTotal, microseconds_t timeDelta) {
+  double valueRange = valueMax - valueMin;
+  double timeRatio = (double) timeDelta / (double) timeTotal;
+  double valueStep = valueRange * timeRatio;
+  double valueNew = max(valueMin, min(valueMax, valueCurrent + valueStep));
+//  Serial.printf("valueCurrent:   %13.3f\n", valueCurrent);
+//  Serial.printf("valueMin:       %13.3f\n", valueMin);
+//  Serial.printf("valueMax:       %13.3f\n", valueMax);
+//  Serial.printf("valueRange:     %13.3f\n", valueRange);
+//  Serial.printf("timeTotal:      %13.3f\n", (double) timeTotal);
+//  Serial.printf("timeDelta:      %13.3f\n", (double) timeDelta);
+//  Serial.printf("timeRatio:      %13.3f\n", timeRatio);
+//  Serial.printf("valueStep:      %13.3f\n", valueStep);
+//  Serial.printf("valueNew:       %13.3f\n", valueNew);
+//  Serial.println();
+  return valueNew;
+}
+
+bool randomBool(int uncertainty) {
+  return random(uncertainty) == 0;
+}
diff --git a/src/BASICS.h b/src/BASICS.h
index de1af91..e18f917 100644
--- a/src/BASICS.h
+++ b/src/BASICS.h
@@ -8,26 +8,8 @@
 
 typedef int64_t microseconds_t;
 
-double step(double valueCurrent, double valueMin, double valueMax, microseconds_t timeTotal, microseconds_t timeDelta) {
-  double valueRange = valueMax - valueMin;
-  double timeRatio = (double) timeDelta / (double) timeTotal;
-  double valueStep = valueRange * timeRatio;
-  double valueNew = max(valueMin, min(valueMax, valueCurrent + valueStep));
-//  Serial.printf("valueCurrent:   %13.3f\n", valueCurrent);
-//  Serial.printf("valueMin:       %13.3f\n", valueMin);
-//  Serial.printf("valueMax:       %13.3f\n", valueMax);
-//  Serial.printf("valueRange:     %13.3f\n", valueRange);
-//  Serial.printf("timeTotal:      %13.3f\n", (double) timeTotal);
-//  Serial.printf("timeDelta:      %13.3f\n", (double) timeDelta);
-//  Serial.printf("timeRatio:      %13.3f\n", timeRatio);
-//  Serial.printf("valueStep:      %13.3f\n", valueStep);
-//  Serial.printf("valueNew:       %13.3f\n", valueNew);
-//  Serial.println();
-  return valueNew;
-}
+double step(double valueCurrent, double valueMin, double valueMax, microseconds_t timeTotal, microseconds_t timeDelta);
 
-bool randomBool(int uncertainty) {
-  return random(uncertainty) == 0;
-}
+bool randomBool(int uncertainty);
 
 #endif
diff --git a/src/display/Display.cpp b/src/display/Display.cpp
new file mode 100644
index 0000000..a46c5be
--- /dev/null
+++ b/src/display/Display.cpp
@@ -0,0 +1,95 @@
+#include "Display.h"
+
+bool SYMBOLS[SYMBOL_COUNT][DISPLAY_CHAR_WIDTH * DISPLAY_CHAR_HEIGHT] = {
+  {
+    X, X, X,
+    X, _, X,
+    X, _, X,
+    X, _, X,
+    X, X, X,
+  },
+  {
+    _, _, X,
+    _, X, X,
+    _, _, X,
+    _, _, X,
+    _, _, X,
+  },
+  {
+    X, X, X,
+    _, _, X,
+    X, X, X,
+    X, _, _,
+    X, X, X,
+  },
+  {
+    X, X, X,
+    _, _, X,
+    _, X, X,
+    _, _, X,
+    X, X, X,
+  },
+  {
+    X, _, X,
+    X, _, X,
+    X, X, X,
+    _, _, X,
+    _, _, X,
+  },
+  {
+    X, X, X,
+    X, _, _,
+    X, X, X,
+    _, _, X,
+    X, X, X,
+  },
+  {
+    X, X, X,
+    X, _, _,
+    X, X, X,
+    X, _, X,
+    X, X, X,
+  },
+  {
+    X, X, X,
+    _, _, X,
+    _, X, _,
+    X, _, _,
+    X, _, _,
+  },
+  {
+    X, X, X,
+    X, _, X,
+    X, X, X,
+    X, _, X,
+    X, X, X,
+  },
+  {
+    X, X, X,
+    X, _, X,
+    X, X, X,
+    _, _, X,
+    X, X, X,
+  },
+  {
+    _, _, _,
+    _, X, _,
+    _, _, _,
+    _, X, _,
+    _, _, _,
+  },
+  {
+    _, _, X,
+    _, _, X,
+    _, _, X,
+    X, _, X,
+    _, X, _,
+  },
+  {
+    X, _, X,
+    X, X, X,
+    _, X, _,
+    X, X, X,
+    X, _, X,
+  },
+};
diff --git a/src/display/Display.h b/src/display/Display.h
index cddbca4..5045dbe 100644
--- a/src/display/Display.h
+++ b/src/display/Display.h
@@ -4,6 +4,12 @@
 #include "Pixel.h"
 #include "Adafruit_NeoPixel.h"
 
+#define SYMBOL_COUNT        13
+#define DISPLAY_CHAR_WIDTH  3
+#define DISPLAY_CHAR_HEIGHT 5
+
+extern bool SYMBOLS[SYMBOL_COUNT][DISPLAY_CHAR_WIDTH * DISPLAY_CHAR_HEIGHT];
+
 class Display {
 
 public:
@@ -33,6 +39,36 @@ public:
       clear();
     }
 
+    void print(uint8_t xPos, uint8_t yPos, uint8_t index, uint8_t r, uint8_t g, uint8_t b) {
+      print(&xPos, yPos, index, r, g, b);
+    }
+
+    void print(uint8_t xPos, uint8_t yPos, uint8_t index) {
+      print(&xPos, yPos, index, 255, 255, 255);
+    }
+
+    void print(uint8_t *xPos, uint8_t yPos, uint8_t index) {
+      print(xPos, yPos, index, 255, 255, 255);
+    }
+
+    void print(uint8_t *xPos, uint8_t yPos, uint8_t index, uint8_t r, uint8_t g, uint8_t b) {
+      if (index >= SYMBOL_COUNT) {
+        Serial.printf("Cannot print symbol #%u.\n", index);
+        return;
+      }
+      bool *symbolBit = SYMBOLS[index];
+      for (uint8_t y = 0; y < DISPLAY_CHAR_HEIGHT; ++y) {
+        for (uint8_t x = 0; x < DISPLAY_CHAR_WIDTH; ++x) {
+          if (*(symbolBit++)) {
+            set(*xPos + x, yPos + y, r, g, b);
+          } else {
+            set(*xPos + x, yPos + y, 0, 0, 0);
+          }
+        }
+      }
+      *xPos += 3;
+    }
+
     void set(uint8_t x, uint8_t y, uint32_t color) {
       setPixelColor(x, y, color);
     }
@@ -67,6 +103,10 @@ public:
       return leds.getBrightness();
     }
 
+    void setIndex(uint16_t index, uint8_t r, uint8_t g, uint8_t b) {
+      leds.setPixelColor(index, r, g, b);
+    }
+
 };
 
 #endif
diff --git a/src/display/Vector.h b/src/display/Vector.h
index 26378a0..abc2ba6 100644
--- a/src/display/Vector.h
+++ b/src/display/Vector.h
@@ -22,6 +22,30 @@ public:
       y = sin(radians) * length;
     }
 
+    Vector *add(Vector that) {
+      this->x += that.x;
+      this->y += that.y;
+      return this;
+    }
+
+    Vector *bounceInBox(uint8_t width, uint8_t height) {
+      while (x < 0 || x >= width) {
+        if (x < 0) {
+          x = -x;
+        } else if (x >= width) {
+          x = 2 * width - x;
+        }
+      }
+      while (y < 0 || y >= height) {
+        if (y < 0) {
+          y = -y;
+        } else if (y >= height) {
+          y = 2 * height - y;
+        }
+      }
+      return this;
+    }
+
 };
 
 #endif
diff --git a/src/main.cpp b/src/main.cpp
index 3a3b66a..ecb2cd5 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -22,7 +22,7 @@ enum ModeId {
 
 Display display(32, 8);
 
-ModeId newModeId = SPACE_INVADERS;
+ModeId newModeId = PONG;
 
 ModeId currentModeId = NONE;
 
@@ -30,7 +30,7 @@ microseconds_t lastMicros = 0;
 
 Mode *mode = nullptr;
 
-double speed = 4.0;
+double speed = 1.0;
 
 bool connected = false;
 
@@ -49,6 +49,26 @@ void setup() {
   Serial.begin(115200);
   Serial.println("\n\n\nStartup!");
   WiFi.begin("HappyNet", "1Grausame!Sackratte7");
+  ArduinoOTA.onStart([]() {
+      display.clear();
+      display.loop();
+  });
+  ArduinoOTA.onProgress([](unsigned int total, unsigned int progress) {
+      double ratio = (double) progress / (double) total;
+      auto index = (uint16_t) round(ratio * (double) display.pixelCount);
+      auto color = (uint8_t) round(ratio * 255.0);
+      display.setIndex(index, 255 - color, color, 0);
+      display.loop();
+  });
+  ArduinoOTA.onEnd([]() {
+      display.clear();
+      display.loop();
+  });
+  ArduinoOTA.onError([](int error) {
+      display.clear();
+      display.loop();
+  });
+
   ArduinoOTA.begin();
   display.setup();
 }
diff --git a/src/mode/Clock/Clock.h b/src/mode/Clock/Clock.h
index 18d66b9..f97aace 100644
--- a/src/mode/Clock/Clock.h
+++ b/src/mode/Clock/Clock.h
@@ -5,88 +5,6 @@
 
 class Clock : public Mode {
 
-private:
-
-    bool SYMBOLS[11][35] = {
-      {
-        X, X, X,
-        X, _, X,
-        X, _, X,
-        X, _, X,
-        X, X, X,
-      },
-      {
-        _, _, X,
-        _, X, X,
-        _, _, X,
-        _, _, X,
-        _, _, X,
-      },
-      {
-        X, X, X,
-        _, _, X,
-        X, X, X,
-        X, _, _,
-        X, X, X,
-      },
-      {
-        X, X, X,
-        _, _, X,
-        _, X, X,
-        _, _, X,
-        X, X, X,
-      },
-      {
-        X, _, X,
-        X, _, X,
-        X, X, X,
-        _, _, X,
-        _, _, X,
-      },
-      {
-        X, X, X,
-        X, _, _,
-        X, X, X,
-        _, _, X,
-        X, X, X,
-      },
-      {
-        X, X, X,
-        X, _, _,
-        X, X, X,
-        X, _, X,
-        X, X, X,
-      },
-      {
-        X, X, X,
-        _, _, X,
-        _, X, _,
-        X, _, _,
-        X, _, _,
-      },
-      {
-        X, X, X,
-        X, _, X,
-        X, X, X,
-        X, _, X,
-        X, X, X,
-      },
-      {
-        X, X, X,
-        X, _, X,
-        X, X, X,
-        _, _, X,
-        X, X, X,
-      },
-      {
-        _, _, _,
-        _, X, _,
-        _, _, _,
-        _, X, _,
-        _, _, _,
-      },
-    };
-
 public:
 
     explicit Clock(Display *display) :
@@ -100,37 +18,22 @@ public:
       return "Clock";
     }
 
-    void step(microseconds_t dt) override {
+    void doStep(microseconds_t dt) override {
       tm time{};
       getLocalTime(&time);
       display->clear();
       uint8_t x = 0;
-      print(&x, time.tm_hour / 10);
+      display->print(&x, 1, time.tm_hour / 10);
       x++;
-      print(&x, time.tm_hour % 10);
-      print(&x, 10);
-      print(&x, time.tm_min / 10);
+      display->print(&x, 1, time.tm_hour % 10);
+      display->print(&x, 1, 10);
+      display->print(&x, 1, time.tm_min / 10);
       x++;
-      print(&x, time.tm_min % 10);
-      print(&x, 10);
-      print(&x, time.tm_sec / 10);
+      display->print(&x, 1, time.tm_min % 10);
+      display->print(&x, 1, 10);
+      display->print(&x, 1, time.tm_sec / 10);
       x++;
-      print(&x, time.tm_sec % 10);
-    }
-
-    void print(uint8_t *pos, uint8_t index) {
-      if (index > 10) {
-        Serial.printf("Cannot print symbol #%u.", index);
-        return;
-      }
-      bool *symbolBit = SYMBOLS[index];
-      for (uint8_t y = 0; y < 5; ++y) {
-        for (uint8_t x = 0; x < 3; ++x) {
-          uint8_t value = *(symbolBit++) ? 255 : 0;
-          display->set(*pos + x, y, value, value, value);
-        }
-      }
-      *pos += 3;
+      display->print(&x, 1, time.tm_sec % 10);
     }
 
 };
diff --git a/src/mode/GameOfLife/Cell.h b/src/mode/GameOfLife/Cell.h
index 3b33d5a..763c476 100644
--- a/src/mode/GameOfLife/Cell.h
+++ b/src/mode/GameOfLife/Cell.h
@@ -14,7 +14,7 @@ public:
     uint32_t color = 0;
 
     void animate(microseconds_t dt) {
-      // TODO "step" does not work as expected
+      // TODO "doStep" does not work as expected
       if (alive) {
         fade = step(fade, 0.0, 255.0, 200000, +dt);
       } else {
diff --git a/src/mode/GameOfLife/GameOfLife.h b/src/mode/GameOfLife/GameOfLife.h
index 1e4eb53..8db088c 100644
--- a/src/mode/GameOfLife/GameOfLife.h
+++ b/src/mode/GameOfLife/GameOfLife.h
@@ -69,7 +69,7 @@ public:
       return "???";
     }
 
-    void step(microseconds_t dt) override {
+    void doStep(microseconds_t dt) override {
       runtime += dt;
       if (runtime >= 500000) {
         runtime = 0;
diff --git a/src/mode/Mode.h b/src/mode/Mode.h
index 7830062..b870bf8 100644
--- a/src/mode/Mode.h
+++ b/src/mode/Mode.h
@@ -1,29 +1,93 @@
 #ifndef MODE_H
 #define MODE_H
 
+#define TIMER_COUNT 10
+
 #include "BASICS.h"
 #include "display/Display.h"
+#include "Timer.h"
 
 class Mode {
 
+private:
+
+    Timer *timers[TIMER_COUNT]{};
+
+    uint8_t timerCount = 0;
+
 protected:
 
     Display *display;
 
-    microseconds_t clock;
-
 public:
 
     explicit Mode(Display *display) :
       display(display) {
-      // nothing
+      for (Timer **timer = timers; timer < timers + TIMER_COUNT; timer++) {
+        *timer = nullptr;
+      }
     }
 
-    virtual ~Mode() = default;
+    virtual ~Mode() {
+      destroyAllTimers();
+    };
 
     virtual const char *getName() = 0;
 
-    virtual void step(microseconds_t dt) = 0;
+    void step(microseconds_t dt) {
+      for (Timer **timer = timers; timer < timers + TIMER_COUNT; timer++) {
+        if (*timer != nullptr) {
+          (*timer)->step(dt);
+        }
+      }
+      doStep(dt);
+    }
+
+protected:
+
+    virtual void doStep(microseconds_t dt) {};
+
+    Timer *createTimer(microseconds_t interval, Timer::Callback callback) {
+      for (Timer **timer = timers; timer < timers + TIMER_COUNT; timer++) {
+        if (*timer == nullptr) {
+          *timer = new Timer(interval, callback);
+          timerCount++;
+          Serial.printf("Timer created: %p (having %u now)\n", *timer, timerCount);
+          return *timer;
+        }
+      }
+      Serial.printf("ERROR: Cannot create more than %d timers!\n", TIMER_COUNT);
+      return nullptr;
+    }
+
+    bool destroyTimer(Timer *t) {
+      for (Timer **timer = timers; timer < timers + TIMER_COUNT; timer++) {
+        if (*timer == t) {
+          _destroyTimer(timer);
+          return true;
+        }
+      }
+      Serial.printf("ERROR: No such timer.\n");
+      return false;
+    }
+
+    void destroyAllTimers() {
+      for (Timer **timer = timers; timer < timers + TIMER_COUNT; timer++) {
+        if (*timer != nullptr) {
+          _destroyTimer(timer);
+        }
+      }
+    }
+
+private:
+
+    void _destroyTimer(Timer **timer) {
+      timerCount--;
+      free(*timer);
+      Serial.printf("Timer destroyed: %p (having %u now)\n", *timer, timerCount);
+      *timer = nullptr;
+    }
+
 };
 
 #endif
diff --git a/src/mode/Pong/Player.h b/src/mode/Pong/Player.h
index 778e0bd..a0e01f9 100644
--- a/src/mode/Pong/Player.h
+++ b/src/mode/Pong/Player.h
@@ -7,10 +7,28 @@ class Player {
 
 public:
 
-    int8_t position = 0;
+    uint8_t position = 0;
+
+    uint8_t size = 2;
 
     uint8_t score = 0;
 
+    bool moveUp = false;
+
+    void randomMove(uint8_t height) {
+      if (moveUp) {
+        position--;
+        if (position <= 0 || randomBool(20)) {
+          moveUp = !moveUp;
+        }
+      } else {
+        position++;
+        if (position + size >= height || randomBool(20)) {
+          moveUp = !moveUp;
+        }
+      }
+    }
+
 };
 
 #endif
diff --git a/src/mode/Pong/Pong.cpp b/src/mode/Pong/Pong.cpp
new file mode 100644
index 0000000..7f39ccf
--- /dev/null
+++ b/src/mode/Pong/Pong.cpp
@@ -0,0 +1,12 @@
+#include "Pong.h"
+
+Pong *Pong::instance = nullptr;
+
+void Pong::resetPlayer() {
+  player0.size = 3;
+  player0.score = 0;
+  player0.position = (display->height - player0.size) / 2;
+  player1.size = 3;
+  player1.score = 0;
+  player1.position = (display->height - player1.size) / 2;
+}
diff --git a/src/mode/Pong/Pong.h b/src/mode/Pong/Pong.h
index 183db84..ccf93a5 100644
--- a/src/mode/Pong/Pong.h
+++ b/src/mode/Pong/Pong.h
@@ -9,6 +9,12 @@ class Pong : public Mode {
 
 private:
 
+    enum Status {
+        SCORE, PLAY, OVER
+    };
+
+    static Pong *instance;
+
     Player player0;
 
     Player player1;
@@ -17,17 +23,119 @@ private:
 
     Vector velocity;
 
+    Status status = PLAY;
+
+    microseconds_t timeout = 0;
+
+    static void tick(Timer *timer, uint32_t totalCount, uint32_t currentCount) {
+      instance->_tick(timer, totalCount, currentCount);
+    }
+
+    void resetPlayer();
+
+    void _tick(Timer *timer, uint32_t totalCount, uint32_t currentCount) {
+      switch (status) {
+        case SCORE:
+          timeout -= currentCount * timer->interval;
+          if (timeout <= 0) {
+            status = PLAY;
+          }
+          break;
+        case PLAY:
+          position.add(velocity);
+          player0.randomMove(display->height);
+          player1.randomMove(display->height);
+          paddleBounce();
+          checkScoring();
+          topBottomBounce();
+          draw();
+          break;
+        case OVER:
+          timeout -= currentCount * timer->interval;
+          if (timeout <= 0) {
+            resetPlayer();
+            status = SCORE;
+            timeout = 2000000;
+          }
+          break;
+      }
+    }
+
+    void topBottomBounce() {
+      position.bounceInBox(display->width, display->height);
+    }
+
+    void checkScoring() {
+      if (position.x < 0) {
+        player1.score++;
+        spawnBall(+1);
+      } else if (position.x >= display->width) {
+        player0.score++;
+        spawnBall(-1);
+      }
+      if (player0.score >= 10 || player1.score >= 10) {
+        status = OVER;
+        timeout = 2000000;
+      }
+    }
+
+    void paddleBounce() {
+      if (position.x == 1 && player0.position <= position.y && position.y < player0.position + player0.size) {
+        velocity.x = -velocity.x;
+        position.x = 3;
+      } else if (position.x == display->width - 2 && player1.position <= position.y && position.y < player1.position + player1.size) {
+        velocity.x = -velocity.x;
+        position.x = display->width - 4;
+      }
+    }
+
+    void spawnBall(int direction) {
+      position.x = (double) display->width / 2.0;
+      position.y = (double) display->height / 2.0;
+      velocity.x = direction;
+      velocity.y = 0;
+      status = SCORE;
+      timeout = 2000000;
+    }
+
+    void draw() {
+      display->clear();
+      switch (status) {
+        case SCORE:
+          display->print(1, 1, player0.score, 0, 255, 0);
+          display->print(display->width - 1 - DISPLAY_CHAR_WIDTH, 1, player1.score, 255, 0, 0);
+          break;
+        case PLAY:
+          for (int i = 0; i < player0.size; ++i) {
+            display->set(1, (uint8_t) round(player0.position) + i, 0, 255, 0);
+          }
+          for (int i = 0; i < player1.size; ++i) {
+            display->set(display->width - 2, (uint8_t) round(player1.position) + i, 255, 0, 0);
+          }
+          display->set((uint8_t) round(position.x), (uint8_t) round(position.y), 255, 255, 255);
+          break;
+        case OVER:
+          if (player0.score > player1.score) {
+            display->print(1, 1, 11, 0, 255, 0);
+            display->print(display->width - 1 - DISPLAY_CHAR_WIDTH, 1, 12, 255, 0, 0);
+          } else if (player0.score < player1.score) {
+            display->print(1, 1, 12, 255, 0, 0);
+            display->print(display->width - 1 - DISPLAY_CHAR_WIDTH, 1, 11, 0, 255, 0);
+          }
+          break;
+      }
+    }
+
 public:
 
     explicit Pong(Display *display) :
       Mode(display),
       position(display->width / 2.0, display->height / 2.0),
       velocity(random(360), exp10(1)) {
-      // nothing
-    }
-
-    static int8_t randomSignum() {
-      return random(2) == 0 ? -1 : +1;
+      instance = this;
+      createTimer(100000, &tick);
+      spawnBall(random(2) == 0 ? -1 : +1);
+      resetPlayer();
     }
 
     ~Pong() override = default;
@@ -36,10 +144,6 @@ public:
       return "Pong";
     }
 
-    void step(microseconds_t dt) override {
-
-    }
-
 };
 
 #endif
diff --git a/src/mode/SpaceInvaders/SpaceInvaders.h b/src/mode/SpaceInvaders/SpaceInvaders.h
index acadfcf..243b8d4 100644
--- a/src/mode/SpaceInvaders/SpaceInvaders.h
+++ b/src/mode/SpaceInvaders/SpaceInvaders.h
@@ -68,7 +68,7 @@ public:
       return "Space Invaders";
     }
 
-    void step(microseconds_t dt) override {
+    void doStep(microseconds_t dt) override {
       stepRockets(dt);
       stepInvaders(dt);
       stepHero(dt);
@@ -80,7 +80,7 @@ public:
         Serial.println("WINNER!");
         reset();
       }
-      if (swarmY + (invadersCountY - 1) * 2 >= display->height - 1) { // TODO this is only correct if there still are any invaders in the last row (otherwise we "Game Over" too early)
+      if (swarmY + (invadersCountY - 1) * 2 >= display->height - 1) { // TODO this is only correct if there still are any invaders in the accu row (otherwise we "Game Over" too early)
         Serial.println("GAME OVER");
         reset();
       }
diff --git a/src/mode/Test/Border.h b/src/mode/Test/Border.h
index 84a5f73..75e3b74 100644
--- a/src/mode/Test/Border.h
+++ b/src/mode/Test/Border.h
@@ -18,7 +18,7 @@ public:
       return "Border";
     }
 
-    void step(microseconds_t dt) override {
+    void doStep(microseconds_t dt) override {
       for (int y = 0; y < display->height; y++) {
         for (int x = 0; x < display->width; x++) {
           if (x == 0 || x == display->width - 1 || y == 0 || y == display->height - 1) {
diff --git a/src/mode/Timer.h b/src/mode/Timer.h
new file mode 100644
index 0000000..4f293bd
--- /dev/null
+++ b/src/mode/Timer.h
@@ -0,0 +1,41 @@
+#ifndef TIMER_H
+#define TIMER_H
+
+#include "BASICS.h"
+
+class Timer {
+
+public:
+
+    typedef void (*Callback)(Timer *timer, uint32_t counter, uint32_t currentCount);
+
+private:
+
+    Callback callback;
+
+    microseconds_t accu = 0;
+
+    uint32_t totalCount = 0;
+
+public:
+
+    microseconds_t interval;
+
+    Timer(microseconds_t interval, Callback callback) :
+      callback(callback),
+      interval(interval) {
+      // nothing
+    }
+
+    void step(microseconds_t dt) {
+      accu += dt;
+      if (accu >= interval) {
+        uint32_t currentCount = accu / interval;
+        accu = accu % interval;
+        callback(this, totalCount++, currentCount);
+      }
+    }
+
+};
+
+#endif