largeimage.c


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#include <avr/io.h>      // this contains all the IO port definitions

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#include <avr/interrupt.h>

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#include <avr/signal.h>

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#include <avr/pgmspace.h>

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#include <util/delay.h>

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void delay_ms( uint16_t milliseconds)

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{

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   for( ; milliseconds > 0; milliseconds--)

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   {

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      _delay_ms( 100);

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   }

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} 

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#define TIMER1_PRESCALE_1 1

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#define TIMER1_PRESCALE_8 2

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#define TIMER1_PRESCALE_64 3

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#define TIMER1_PRESCALE_256 4

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#define TIMER1_PRESCALE_1024 5

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// We use these macros because binary constants arent always supported. ugh.

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#define HEX__(n) 0x##n##UL

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#define B8__(x) ((x&0x0000000FLU)?1:0)  \

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               +((x&0x000000F0LU)?2:0)  \

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               +((x&0x00000F00LU)?4:0)  \

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               +((x&0x0000F000LU)?8:0)  \

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               +((x&0x000F0000LU)?16:0) \

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               +((x&0x00F00000LU)?32:0) \

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               +((x&0x0F000000LU)?64:0) \

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               +((x&0xF0000000LU)?128:0)

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#define B8(d) ((unsigned char)B8__(HEX__(d)))

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// store all the image data in program memory (ROM)

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// instead of RAM (the default)

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const uint8_t large_image[] PROGMEM = {

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(11111111),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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B8(00000000),

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};

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// special pointer for reading from ROM memory

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PGM_P largeimage_p PROGMEM = large_image;

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#define NUM_ELEM(x) (sizeof (x) / sizeof (*(x)))

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int imagesize = NUM_ELEM(large_image);

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// this function is called when timer1 compare matches OCR1A

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uint8_t j = 0;

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SIGNAL( SIG_TIMER1_COMPA ) {

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  if (j >= imagesize) 

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    j = 0;

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  // read the image data from ROM

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  PORTB = pgm_read_byte(largeimage_p + j); 

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  j++;

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}

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int main(void) {

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  DDRB = 0xFF;       // set all 8 pins on port B to outputs

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  /*

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    the frequency of the interrupt overflow is determined by the 

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    prescaler and overflow value.

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    freq = clock_frequency / ( 2 * prescaler * overflow_val)

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    where prescaler can be 1, 8, 64, 256, or 1024

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    clock_freq is 8MHz

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    and overflow_val is 16bit

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    the overflow value is placed in OCR1A, the prescale is set in TCCR1B

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    so for example:

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    A good POV frequency is around 400Hz

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    desired freq = 400Hz

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    clock freq = 8MHz

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    8MHz / (400Hz * 2) = 10000

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    since 10000 is less than 655536 (largest 16 bit number)

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    OCR1A = 10000 and the prescale is 1

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  */

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  TCCR1B = (1 << WGM12) | TIMER1_PRESCALE_1;

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  OCR1A = (uint16_t)10000;

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  TIMSK |= 1 << OCIE1A;   // Output Compare Interrupt Enable (timer 1, OCR1A) 

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  sei();                 // Set Enable Interrupts

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  while (1);

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}