#include <avr/io.h>
#include <avr/interrupt.h>
// define the processor speed if it's not been defined at the compilers command line.
#ifndef F_CPU
#define F_CPU 1000000
#endif
volatile uint8_t g_timeslice[8] ; // one byte for each bit-position being displayed on a port.
volatile uint8_t g_tick = 0;
volatile uint8_t g_bitpos = 0; // which bit position is currently being shown
void led_init( void ) ;
void led_encode_timeslices( uint8_t a[] );
__attribute((OS_main)) int main(void)
{
uint8_t brightness[8]; // brightness for each LED on port D.
led_init();
led_encode_timeslices( brightness ) ;
sei();
// now a (simple) demonstration...
// In the real-world, you'd probably want to decouple the
// animation speed from the LED flicker-rate.
uint8_t slowtick = 30;
uint8_t position = 0 ;
while(1)
{
while(g_tick==0){ /*wait for g_tick to be non-zero*/ }
g_tick = 0 ; //consume the tick
// make each of the LEDs slightly dimmer...
for ( uint8_t index = 0 ; index < 8 ; index++ )
{
if (brightness[ index ] > 0) brightness[ index ]-- ;
}
// once every 50 ticks, advance the head of the sweep...
slowtick-- ;
if (slowtick==0)
{
slowtick = 30;
position++ ;
position &= 7 ;
brightness[ position ] = 100 ;
}
// and now re-encode all the timeslices...
led_encode_timeslices( brightness ) ;
}
return(0);
}
// simple initialisation of the port and timer
void led_init( void )
{
PORTD = 0x00 ; // All outputs to 0.
DDRD = 0xff ; // All outputs.
TCCR2 |= (1<<WGM21) ; // set the timer to CTC mode.
TCCR2 |= ((1<<CS21)|(1<<CS20)) ; // use clock/32 tickrate
g_bitpos = 0 ;
OCR2 = 1 ; // initial delay.
TIMSK |= (1 << OCIE2) ; // Enable the Compare Match interrupt
}
// encode an array of 8 LED brightness bytes into the pattern
// to be shown on the port for each of the 8 timeslices.
void led_encode_timeslices( uint8_t intensity[] )
{
uint8_t portbits = 0;
uint8_t bitvalue ;
for ( uint8_t bitpos = 0 ; bitpos < 8 ; bitpos++ )
{
portbits = 0;
bitvalue = 1 ;
for ( uint8_t ledpos = 0 ; ledpos < 8 ; ledpos++ )
{
if (intensity[ ledpos ] & (1 << bitpos)) portbits |= bitvalue ;
bitvalue = bitvalue << 1 ;
}
g_timeslice[ bitpos ] = portbits ;
}
}
// Timer interrupt handler - called once per bit position.
ISR( TIMER2_COMP_vect )
{
g_bitpos ++ ;
g_bitpos &= 7;
PORTD = g_timeslice[ g_bitpos ] ;
// now set the delay...
TCNT2 = 0;
OCR2 <<= 1 ;
if (g_bitpos == 0) OCR2 = 1 ; // reset the compare match value.
if (g_bitpos == 7) g_tick = 1 ; // give the main loop a kick.
}
