blinky.c

/* function to read value from one port, and control the led blinking on another
port by transferring data of the read port to the controlling port
data read from port B, and led controlled from port D */
// ATmega8, clock freq=1 MHz.
#include <avr/io.h>
#include<util/delay.h>
#include<math.h>
int main(void) {
unsigned int polarity=0;
unsigned int speed=0;
double speed_n;
int i;
DDRB=0x00;  //port B set as input
DDRD=0xFF;  //port D set as output
PORTD=PINB;//port B input transferred to port D, PINB is register storing input data for port B
while(1)
{
// polarity will be 0 or 1 based on whether B7 is low or high
PINB>127?(polarity=1):(polarity=0); // for PINB to be > 127, B7 must be high
speed=(PINB)&(0x7F);                    //masking B7, thus B0 to B6 value will result in speed control
speed_n=(log10(speed)/log10(2));        //thus speed_n contains which(nth) multiple of 2 is the data read at Port B
for(i=1;i<=128;i*=2)
{
if(polarity)
PORTD=~i;           //if B7 is high, then polarity=1, and Port D displays inverse of i
else
PORTD=i;
_delay_ms(100+(speed_n*50));
}
for(i=128;i>1;i-=i/2)
{
if(polarity)
PORTD=~i;
else
PORTD=i;
_delay_ms(100+(speed_n*50));
}
}return(1);
}