gg-button/gg.c

#include <avr/io.h>
#include <util/delay.h>
#include <avr/interrupt.h>

#include "mmc.h"


void timer_init_tiny26(void)
{
	PLLCSR = 1 << PLLE;/* pll enable */
	_delay_us(100);
	while(!(PLLCSR & (1 << PLOCK))) {;}/* wait for lock */
	PLLCSR |= 1 << PCKE;/* use pll */
	
	OCR1C = 0xff;/* unused */
	
	/* output pin: OC1A = PB1 = 1 or OC1B = PB3 = 2 */
	OCR1A = 0;
	TCCR1A = (1 << COM1A1) | (1 << PWM1A);/* pwm enable, not inverted */
	TCCR1B = (1 << CS10);/* fast pwm, no prescaler */
	DDRB |= (1 << PB1);
	
	TIMSK = 1 << TOIE1;/* interrupt on overflow */
}


uint8_t length[4];/* remaining samples */
uint32_t mmc_position;/* current reading position on mmc */

uint8_t overflows = 1;/* remaining counter overflows until next sample */
#define SAMPLE_BITS 11

#define BUFFER_SIZE 64
#define REFRESH_AMOUNT 32
#define REFRESH_SIZE (BUFFER_SIZE - REFRESH_AMOUNT)
uint8_t buffer[BUFFER_SIZE];/* buffer for mmc data */

uint8_t pos = 0;/* current playing position */
uint8_t refresh_buffer = 0;/* position to start buffer refreshing */

ISR(TIMER1_OVF1_vect)
{
	//if(!(TIFR & (1 << TOV1))) {continue;}/* interrupt flag polling */
	//TIFR |= (1 << TOV1);/* done by hardware */
	
	overflows--;
	if(!overflows)
	{
		overflows = 1 << (SAMPLE_BITS - 8);
		pos = (pos + 1) % BUFFER_SIZE;
	}
	
	/* TODO: a-law decoding */
	/* TODO: 11bit PWM emulation */
	OCR1A = buffer[pos];/* play sample */
}



int main(void) __attribute__((noreturn));
int main(void)
{
    uint8_t ref; // TODO: what does this do?
	if(mmc_init() != 0) {/* mmc fail */;}
	timer_init_tiny26();
	sei();
	
	for(;;)
	{
		if(pos == refresh_buffer)/* refresh buffer if running low */
		{
			/* TODO: this won't do. we don't have enough time to read unnecessary bytes -> read data with the same speed as we consume it, keeping a small buffer. */
			/* expect 2 bit read from mmc between 2 timer interrupts --> 2 byte read per sample played */
			
			mmc_read_sector(mmc_position, buffer + (ref + REFRESH_SIZE) % BUFFER_SIZE);//, BUFFER_SIZE - ref), buffer, REFRESH_AMOUNT - (BUFFER_SIZE - ref));
			/*       pos on sd   , first buffer address                       , 1st buffer size  ,2nd buf, 2nd buffer size                    */
			refresh_buffer = (refresh_buffer + REFRESH_AMOUNT) % BUFFER_SIZE;
		}
	}
}