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90 lines
2.1 KiB
C
90 lines
2.1 KiB
C
15 years ago
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/*
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* ----------------------------------------------------------------------------
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* "THE BEER-WARE LICENSE" (Revision 42):
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* <joerg@FreeBSD.ORG> wrote this file. As long as you retain this notice you
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* can do whatever you want with this stuff. If we meet some day, and you think
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* this stuff is worth it, you can buy me a beer in return. Joerg Wunsch
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* ----------------------------------------------------------------------------
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*
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* Simple AVR demonstration. Controls a LED that can be directly
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* connected from OC1/OC1A to GND. The brightness of the LED is
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* controlled with the PWM. After each period of the PWM, the PWM
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* value is either incremented or decremented, that's all.
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*
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* $Id: demo.c,v 1.9 2006/01/05 21:30:10 joerg_wunsch Exp $
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*/
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#include <inttypes.h>
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#include <avr/io.h>
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#include <avr/interrupt.h>
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#include <avr/sleep.h>
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#include "iocompat.h" /* Note [1] */
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enum { UP, DOWN };
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ISR (TIMER1_OVF_vect) /* Note [2] */
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{
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static uint16_t pwm; /* Note [3] */
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static uint8_t direction;
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switch (direction) /* Note [4] */
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{
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case UP:
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if (++pwm == TIMER1_TOP)
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direction = DOWN;
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break;
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case DOWN:
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if (--pwm == 0)
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direction = UP;
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break;
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}
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OCR = pwm; /* Note [5] */
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}
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void
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ioinit (void) /* Note [6] */
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{
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/* Timer 1 is 10-bit PWM (8-bit PWM on some ATtinys). */
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TCCR1A = TIMER1_PWM_INIT;
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/*
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* Start timer 1.
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*
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* NB: TCCR1A and TCCR1B could actually be the same register, so
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* take care to not clobber it.
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*/
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TCCR1B |= TIMER1_CLOCKSOURCE;
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/*
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* Run any device-dependent timer 1 setup hook if present.
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*/
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#if defined(TIMER1_SETUP_HOOK)
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TIMER1_SETUP_HOOK();
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#endif
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/* Set PWM value to 0. */
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OCR = 0;
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/* Enable OC1 as output. */
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DDROC = _BV (OC1);
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/* Enable timer 1 overflow interrupt. */
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TIMSK = _BV (TOIE1);
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sei ();
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}
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int
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main (void)
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{
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ioinit ();
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/* loop forever, the interrupts are doing the rest */
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for (;;) /* Note [7] */
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sleep_mode();
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return (0);
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}
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