avr/blink/helloworld.c

   1 #define F_CPU 1000000UL // Sets up the default speed for delay.h
   2 // this is the header file that tells the compiler what pins and ports, etc.
   3 // are available on this chip.
   4 #include <avr/io.h>
   5
   6 // define what pins the LEDs are connected to.
   7 // in reality, PD6 is really just '6'
   8 #define LED PD5
   9
  10 // Some macros that make the code more readable
  11 #define output_low(port,pin) port &= ~(1<<pin)
  12 #define output_high(port,pin) port |= (1<<pin)
  13 #define set_input(portdir,pin) portdir &= ~(1<<pin)
  14 #define set_output(portdir,pin) portdir |= (1<<pin)
  15
  16 // this is just a program that 'kills time' in a calibrated method
  17 void delay_ms(uint8_t ms) {
  18   uint16_t delay_count = F_CPU / 17500;
  19   volatile uint16_t i;
  20
  21   while (ms != 0) {
  22     for (i=0; i != delay_count; i++);
  23     ms--;
  24   }
  25 }
  26
  27 int main(void) {
  28   // initialize the direction of PORTD #6 to be an output
  29   set_output(DDRD, LED);
  30
  31   while (1) {
  32     // turn on the LED for 200ms
  33     output_high(PORTD, LED);
  34     delay_ms(200);
  35     // now turn off the LED for another 200ms
  36     output_low(PORTD, LED);
  37     delay_ms(200);
  38     // now start over
  39   }
  40 }