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#include <avr/io.h> // this contains all the IO port definitions
#include <avr/interrupt.h>
#include <avr/pgmspace.h>
#include <util/delay.h>
void delay_ms( uint16_t milliseconds)
{
for( ; milliseconds > 0; milliseconds--)
{
_delay_ms( 1);
}
}
#define TIMER1_PRESCALE_1 1
#define TIMER1_PRESCALE_8 2
#define TIMER1_PRESCALE_64 3
#define TIMER1_PRESCALE_256 4
#define TIMER1_PRESCALE_1024 5
// We use these macros because binary constants arent always supported. ugh.
#define HEX__(n) 0x##n##UL
#define B8__(x) ((x&0x0000000FLU)?1:0) \
+((x&0x000000F0LU)?2:0) \
+((x&0x00000F00LU)?4:0) \
+((x&0x0000F000LU)?8:0) \
+((x&0x000F0000LU)?16:0) \
+((x&0x00F00000LU)?32:0) \
+((x&0x0F000000LU)?64:0) \
+((x&0xF0000000LU)?128:0)
#define B8(d) ((unsigned char)B8__(HEX__(d)))
// store all the image data in program memory (ROM)
// instead of RAM (the default)
const uint8_t bmp_image[] PROGMEM = {
B8(00000000),
B8(00000000),
B8(01110000),
B8(10001000),
B8(10000100),
B8(10000010),
B8(01000001),
B8(10000010),
B8(10000100),
B8(10001000),
B8(01110000),
B8(00000000),
B8(00000000),
};
// special pointer for reading from ROM memory
PGM_P const bmpimage_p PROGMEM = bmp_image;
#define NUM_ELEM(x) (sizeof (x) / sizeof (*(x)))
int imagesize = NUM_ELEM(bmp_image);
// this function is called when timer1 compare matches OCR1A
uint8_t j = 0;
SIGNAL( TIMER1_COMPA_vect ) {
if (j >= imagesize)
j = 0;
// read the image data from ROM
PORTB = pgm_read_byte(bmpimage_p + j);
j++;
}
int main(void) {
DDRB = 0xFF; // set all 8 pins on port B to outputs
/*
the frequency of the interrupt overflow is determined by the
prescaler and overflow value.
freq = clock_frequency / ( 2 * prescaler * overflow_val)
where prescaler can be 1, 8, 64, 256, or 1024
clock_freq is 8MHz
and overflow_val is 16bit
the overflow value is placed in OCR1A, the prescale is set in TCCR1B
so for example:
A good POV frequency is around 400Hz
desired freq = 400Hz
clock freq = 8MHz
8MHz / (400Hz * 2) = 10000
since 10000 is less than 655536 (largest 16 bit number)
OCR1A = 10000 and the prescale is 1
*/
TCCR1B = (1 << WGM12) | TIMER1_PRESCALE_1;
OCR1A = (uint16_t)10000;
TIMSK |= 1 << OCIE1A; // Output Compare Interrupt Enable (timer 1, OCR1A)
sei(); // Set Enable Interrupts
while (1);
}