diff --git a/src/draw.c b/src/draw.c
index 286a40f..7bec443 100644
--- a/src/draw.c
+++ b/src/draw.c
@@ -7,7 +7,7 @@
 
 #define BYTES_PER_PIXEL 2
 
-uint16_t bitmap_draw(   unsigned int width, unsigned int height,
+int8_t bitmap_draw(    unsigned int width, unsigned int height,
                         unsigned int bytes_per_pixel,
                         const unsigned char *pixel_data){
     
diff --git a/src/draw.h b/src/draw.h
index 12d13af..db8efe1 100644
--- a/src/draw.h
+++ b/src/draw.h
@@ -7,11 +7,10 @@
  * @param       width               Bitmap width
  * @param       height              Bitmap height
  * @param       bytes_per_pixel     Bytes per pixel
- * @param       color               16-Bit color bitmap
- * @param       *pixel_data         uint16_t Bitmap data array 
+ * @param       pixel_data         uint16_t Bitmap data array 
  * @return      -1 if error 0 else
  *
  */
-uint16_t bitmap_draw(unsigned int width, unsigned int height, unsigned int bytes_per_pixel, const unsigned char *pixel_data);
+int8_t bitmap_draw(unsigned int width, unsigned int height, unsigned int bytes_per_pixel, const unsigned char *pixel_data);
 
 #endif /* DRAW_H */
diff --git a/src/io.h b/src/io.h
index aa9199c..30b944b 100644
--- a/src/io.h
+++ b/src/io.h
@@ -34,8 +34,13 @@ bool io_button_has_edge(uint8_t btnnumber);
 uint16_t read_adc();
 
 
-#define ADC_MASK 0x3FF
+//Mask for the ADC value (to cut away bits which cannot be valid)
+#define ADC_MASK 0x3FF 
+
+//Value that should be threated as maximum
 #define ADC_MAX 0x3A0
+
+//Tolerance value. Changes below this value will be ignored.
 #define ADC_TOLERANCE 0x08
 
 
diff --git a/src/io.s b/src/io.s
index ce732bf..ef31c7c 100644
--- a/src/io.s
+++ b/src/io.s
@@ -11,10 +11,10 @@ typedef struct pin_s {
 .set OFFSET_PIN_PINMASK, 4
 
     
-//--------Local Functions ------------------ 
+//--------Functions ------------------ 
+//See the doxygen comments in the headerfiles for the parameter documentation of the following functions
 .text
 
-
 //void pin_create(pin_t* pin, GPIO_TypeDef* GPIO, uint8_t pinnr)
 .global pin_create
 
@@ -28,7 +28,7 @@ pin_create:
     .set GPIO_PuPd_UP, 1
     .set GPIO_OType_OD, 1
 
-    PUSH {r4,r5,r6,lr}
+    PUSH {r4,r5,r6,lr} //Save registers
 
     LSL r4, r2, #1 //r4 = pinnr*2
     MOV r5, #3 //r5 = 3
@@ -72,7 +72,7 @@ pin_create:
     //pin->pinmask=0x01<<pinnr; // Insert the pinmask
     STRH r5, [r0, #OFFSET_PIN_PINMASK]
 
-    POP {r4, r5, r6, pc}
+    POP {r4, r5, r6, pc} //Restore registers
 
 end_pin_create:
 
@@ -84,7 +84,9 @@ end_pin_create:
 pin_get:
          
    .set GPIO_IDR, 0x10
-    //return ((pin->GPIO->IDR & pin->pinmask) > 0);
+
+    //C-Code (one liner) return ((pin->GPIO->IDR & pin->pinmask) > 0);
+   
    LDR r1, [r0, #OFFSET_PIN_GPIO] //r1 = pin->GPIO
    LDR r1, [r1,#GPIO_IDR] // r1 = pin->GPIO->IDR 
    LDRH r2, [r0, #OFFSET_PIN_PINMASK] // r2 = pin->pinmask
@@ -93,13 +95,14 @@ pin_get:
 
    MOV r0, #1 //return 1
    MOV pc, lr
+
 pin_get_eq:
    MOV r0, #0 //return 0
    MOV pc, lr
+
 end_pin_get:
 
 
-//-------Global Functions-------------------
 //void adc_init(void);
 .global adc_init
 
diff --git a/src/io_c.c b/src/io_c.c
index 915372e..a0eae4d 100644
--- a/src/io_c.c
+++ b/src/io_c.c
@@ -2,42 +2,44 @@
 #include <carme_io2.h>
 #include "io.h"
 
-
+//Structure which holds the configuration for one (input) pin (GPIO).
 typedef struct pin_s {
-    GPIO_TypeDef* GPIO;
-    uint16_t pinmask;
+    GPIO_TypeDef* GPIO; //GPIO port which is used
+    uint16_t pinmask; //Pin Nr (0..15)
 } pin_t;
 
 // Local variables
+// Pin structs for the pins T0..T3
 static pin_t pin_t0;
 static pin_t pin_t1;
 static pin_t pin_t2;
 static pin_t pin_t3;
-static uint8_t new = 0;
-static uint8_t old = 0;
-static volatile uint8_t edg = 0;
+
+//Variables for the edge detection
+static uint8_t old = 0; //old state of the buttons
+static volatile uint8_t edg = 0; //detected edges
 
 //Function prototypes of functions that are implemented in asm
-void pin_create(pin_t* pin, GPIO_TypeDef* GPIO, uint8_t pinnr);
-bool pin_get(pin_t* pin);
-bool adc_init();
-
+void pin_create(pin_t* pin, GPIO_TypeDef* GPIO, uint8_t pinnr); //Initializes the pin structure and the gpio with the passed data.
+bool pin_get(pin_t* pin); //Returns the current state of the pin (true = pin is "high")
+bool adc_init(); //Initializes the adc and configures the channel
 
 void io_process(void) {
-    new = pin_get(&pin_t0)      |
-          pin_get(&pin_t1) << 1 |
-          pin_get(&pin_t2) << 2 |
-          pin_get(&pin_t3) << 3;
+    //Save the current state of the 4 pins in the lower nibble
+    uint8_t new = pin_get(&pin_t0) |
+            pin_get(&pin_t1) << 1  |
+            pin_get(&pin_t2) << 2  |
+            pin_get(&pin_t3) << 3;
 
     edg |= (new ^ old) & new;    // detect positive edge
-    old = new;
+    old = new; //store current state, for later edge detection
 }
 
 bool io_button_has_edge(uint8_t btnnumber) {
     uint8_t bm      = (1 << btnnumber); // create bitmask
     bool status     = ((edg & bm) > 0); // check if button is pressed
     
-    if(status){
+    if(status) { // if button is pressed
         edg &= ~bm; // clear edge bit
     }
 
@@ -45,14 +47,16 @@ bool io_button_has_edge(uint8_t btnnumber) {
 }
 
 void io_init(void){
+    //Enable clock for gpio
     //RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA | RCC_AHB1Periph_GPIOC,ENABLE); // Enable gpio clock source
     RCC->AHB1ENR|= RCC_AHB1Periph_GPIOA | RCC_AHB1Periph_GPIOB | RCC_AHB1Periph_GPIOC | RCC_AHB1Periph_GPIOI;
+
     // Create player pins
     pin_create(&pin_t0, GPIOC, 7);  // create pin_t0
     pin_create(&pin_t1, GPIOB, 15); // create pin_t1
     pin_create(&pin_t2, GPIOB, 14); // create pin_t2
     pin_create(&pin_t3, GPIOI, 0);  // create pin_t3
 
-    adc_init();
+    adc_init(); //Initialize adc
 
 }
diff --git a/src/main.c b/src/main.c
index c1d0b6a..7f09a7b 100644
--- a/src/main.c
+++ b/src/main.c
@@ -31,18 +31,21 @@
 #include "game.h"
 #include "uart.h"
 
+//Game Object, which contains the entire state of the game
+//Exchange this object via Uart, to have remote players
 game_t gameobj;
 
-uint64_t ticks;
-uint64_t lastTicks;
+volatile uint64_t ticks = 0; //Ticks since reset
+uint64_t lastTicks = 0; //Last tick
 
+//SysTick Handler that will be called several times per second (see TICKS_PER_SECOND). This is an interrupt.
 void SysTick_Handler() {
-    ticks++;
-    io_process();
+    ticks++; 
+    io_process(); //Process button presses
 }
 
-#define SYSCLK              168e6
-#define TICKS_PER_SECOND    1000
+#define SYSCLK              168e6 //System frequency
+#define TICKS_PER_SECOND    1000 //Number of SysTick interrupts that should occour ( = number of times SysTick_Handler calls per sec)
 
 int main(void)
 {
@@ -50,13 +53,14 @@ int main(void)
         while(1); //sleep forever
     }
 
-    game_init(&gameobj, TICKS_PER_SECOND);
+    game_init(&gameobj, TICKS_PER_SECOND); //Init game state
+
     while(1) {
         uint64_t curTicks = ticks;
-        if(game_step(&gameobj,curTicks-lastTicks)) { //calculate next game step, and pass it the delta time
-            lastTicks = ticks;
+        if(game_step(&gameobj,curTicks-lastTicks)) { //calculate next game step, and pass it the delta time. Returns true if function was blocking
+            lastTicks = ticks; //Save actual ticks
         } else {
-            lastTicks = curTicks;
+            lastTicks = curTicks; //Save ticks from before calling game_step
         }
     }