@WizenedEE Thank you for your great code example. That is the solution which works fine now. My test LED blinks with 485-490Hz which is 970-980 interrupt calls per second. My Oscilloscope can't measure more precise than this, but it makes the calculated 976 Hz quite believable
In order to conveniently add my code to Arduino timer0 interrupt code, I extended wiring.c and Arduino.h by a new function. Now I can simply define a new function in my sketch e.g. named myISR(), call the new function attachTimerInt0Extension( myISR ) and from now on myISR() is executed right after the original Arduino Interrupt code.
If you look for //SRO you find my additions to the original files:
wiring.c
#include "wiring_private.h"
// the prescaler is set so that timer0 ticks every 64 clock cycles, and the
// the overflow handler is called every 256 ticks.
#define MICROSECONDS_PER_TIMER0_OVERFLOW (clockCyclesToMicroseconds(64 * 256))
// the whole number of milliseconds per timer0 overflow
#define MILLIS_INC (MICROSECONDS_PER_TIMER0_OVERFLOW / 1000)
// the fractional number of milliseconds per timer0 overflow. we shift right
// by three to fit these numbers into a byte. (for the clock speeds we care
// about - 8 and 16 MHz - this doesn't lose precision.)
#define FRACT_INC ((MICROSECONDS_PER_TIMER0_OVERFLOW % 1000) >> 3)
#define FRACT_MAX (1000 >> 3)
volatile unsigned long timer0_overflow_count = 0;
volatile unsigned long timer0_millis = 0;
static unsigned char timer0_fract = 0;
//SRO______Legt einen Funktionszeiger an______________________________
void (*int0Extender)();
//__________________________________________________________________
#if defined(__AVR_ATtiny24__) || defined(__AVR_ATtiny44__) || defined(__AVR_ATtiny84__)
SIGNAL(TIM0_OVF_vect)
#else
SIGNAL(TIMER0_OVF_vect)
#endif
{
// copy these to local variables so they can be stored in registers
// (volatile variables must be read from memory on every access)
unsigned long m = timer0_millis;
unsigned char f = timer0_fract;
m += MILLIS_INC;
f += FRACT_INC;
if (f >= FRACT_MAX) {
f -= FRACT_MAX;
m += 1;
}
timer0_fract = f;
timer0_millis = m;
timer0_overflow_count++;
//SRO_______Timer 0 um eigene Funktion in Arduino erweitern_____
if(int0Extender)
int0Extender();
//______________________________________________________________
}
//SRO______________ meine Timer0 Ergänzung_________________________
void attachTimerInt0Extension(void (*myISR)())
{
int0Extender = myISR;
}
//_________________________________________________________________
unsigned long millis()
{
unsigned long m;
uint8_t oldSREG = SREG;
// disable interrupts while we read timer0_millis or we might get an
// inconsistent value (e.g. in the middle of a write to timer0_millis)
cli();
m = timer0_millis;
SREG = oldSREG;
return m;
}
unsigned long micros() {
unsigned long m;
uint8_t oldSREG = SREG, t;
cli();
m = timer0_overflow_count;
#if defined(TCNT0)
t = TCNT0;
#elif defined(TCNT0L)
t = TCNT0L;
#else
#error TIMER 0 not defined
#endif
#ifdef TIFR0
if ((TIFR0 & _BV(TOV0)) && (t < 255))
m++;
#else
if ((TIFR & _BV(TOV0)) && (t < 255))
m++;
#endif
SREG = oldSREG;
return ((m << 8) + t) * (64 / clockCyclesPerMicrosecond());
}
void delay(unsigned long ms)
{
uint16_t start = (uint16_t)micros();
while (ms > 0) {
if (((uint16_t)micros() - start) >= 1000) {
ms--;
start += 1000;
}
}
}
/* Delay for the given number of microseconds. Assumes a 8 or 16 MHz clock. */
void delayMicroseconds(unsigned int us)
{
// calling avrlib's delay_us() function with low values (e.g. 1 or
// 2 microseconds) gives delays longer than desired.
//delay_us(us);
#if F_CPU >= 16000000L
// for the 16 MHz clock on most Arduino boards
// for a one-microsecond delay, simply return. the overhead
// of the function call yields a delay of approximately 1 1/8 us.
if (--us == 0)
return;
// the following loop takes a quarter of a microsecond (4 cycles)
// per iteration, so execute it four times for each microsecond of
// delay requested.
us <<= 2;
// account for the time taken in the preceeding commands.
us -= 2;
#else
// for the 8 MHz internal clock on the ATmega168
// for a one- or two-microsecond delay, simply return. the overhead of
// the function calls takes more than two microseconds. can't just
// subtract two, since us is unsigned; we'd overflow.
if (--us == 0)
return;
if (--us == 0)
return;
// the following loop takes half of a microsecond (4 cycles)
// per iteration, so execute it twice for each microsecond of
// delay requested.
us <<= 1;
// partially compensate for the time taken by the preceeding commands.
// we can't subtract any more than this or we'd overflow w/ small delays.
us--;
#endif
// busy wait
__asm__ __volatile__ (
"1: sbiw %0,1" "\n\t" // 2 cycles
"brne 1b" : "=w" (us) : "0" (us) // 2 cycles
);
}
void init()
{
// this needs to be called before setup() or some functions won't
// work there
sei();
// on the ATmega168, timer 0 is also used for fast hardware pwm
// (using phase-correct PWM would mean that timer 0 overflowed half as often
// resulting in different millis() behavior on the ATmega8 and ATmega168)
#if defined(TCCR0A) && defined(WGM01)
sbi(TCCR0A, WGM01);
sbi(TCCR0A, WGM00);
#endif
// set timer 0 prescale factor to 64
#if defined(__AVR_ATmega128__)
// CPU specific: different values for the ATmega128
sbi(TCCR0, CS02);
#elif defined(TCCR0) && defined(CS01) && defined(CS00)
// this combination is for the standard atmega8
sbi(TCCR0, CS01);
sbi(TCCR0, CS00);
#elif defined(TCCR0B) && defined(CS01) && defined(CS00)
// this combination is for the standard 168/328/1280/2560
sbi(TCCR0B, CS01);
sbi(TCCR0B, CS00);
#elif defined(TCCR0A) && defined(CS01) && defined(CS00)
// this combination is for the __AVR_ATmega645__ series
sbi(TCCR0A, CS01);
sbi(TCCR0A, CS00);
#else
#error Timer 0 prescale factor 64 not set correctly
#endif
// enable timer 0 overflow interrupt
#if defined(TIMSK) && defined(TOIE0)
sbi(TIMSK, TOIE0);
#elif defined(TIMSK0) && defined(TOIE0)
sbi(TIMSK0, TOIE0);
#else
#error Timer 0 overflow interrupt not set correctly
#endif
// timers 1 and 2 are used for phase-correct hardware pwm
// this is better for motors as it ensures an even waveform
// note, however, that fast pwm mode can achieve a frequency of up
// 8 MHz (with a 16 MHz clock) at 50% duty cycle
#if defined(TCCR1B) && defined(CS11) && defined(CS10)
TCCR1B = 0;
// set timer 1 prescale factor to 64
sbi(TCCR1B, CS11);
#if F_CPU >= 8000000L
sbi(TCCR1B, CS10);
#endif
#elif defined(TCCR1) && defined(CS11) && defined(CS10)
sbi(TCCR1, CS11);
#if F_CPU >= 8000000L
sbi(TCCR1, CS10);
#endif
#endif
// put timer 1 in 8-bit phase correct pwm mode
#if defined(TCCR1A) && defined(WGM10)
sbi(TCCR1A, WGM10);
#elif defined(TCCR1)
#warning this needs to be finished
#endif
// set timer 2 prescale factor to 64
#if defined(TCCR2) && defined(CS22)
sbi(TCCR2, CS22);
#elif defined(TCCR2B) && defined(CS22)
sbi(TCCR2B, CS22);
#else
#warning Timer 2 not finished (may not be present on this CPU)
#endif
// configure timer 2 for phase correct pwm (8-bit)
#if defined(TCCR2) && defined(WGM20)
sbi(TCCR2, WGM20);
#elif defined(TCCR2A) && defined(WGM20)
sbi(TCCR2A, WGM20);
#else
#warning Timer 2 not finished (may not be present on this CPU)
#endif
#if defined(TCCR3B) && defined(CS31) && defined(WGM30)
sbi(TCCR3B, CS31); // set timer 3 prescale factor to 64
sbi(TCCR3B, CS30);
sbi(TCCR3A, WGM30); // put timer 3 in 8-bit phase correct pwm mode
#endif
#if defined(TCCR4B) && defined(CS41) && defined(WGM40)
sbi(TCCR4B, CS41); // set timer 4 prescale factor to 64
sbi(TCCR4B, CS40);
sbi(TCCR4A, WGM40); // put timer 4 in 8-bit phase correct pwm mode
#endif
#if defined(TCCR5B) && defined(CS51) && defined(WGM50)
sbi(TCCR5B, CS51); // set timer 5 prescale factor to 64
sbi(TCCR5B, CS50);
sbi(TCCR5A, WGM50); // put timer 5 in 8-bit phase correct pwm mode
#endif
#if defined(ADCSRA)
// set a2d prescale factor to 128
// 16 MHz / 128 = 125 KHz, inside the desired 50-200 KHz range.
// XXX: this will not work properly for other clock speeds, and
// this code should use F_CPU to determine the prescale factor.
sbi(ADCSRA, ADPS2);
sbi(ADCSRA, ADPS1);
sbi(ADCSRA, ADPS0);
// enable a2d conversions
sbi(ADCSRA, ADEN);
#endif
// the bootloader connects pins 0 and 1 to the USART; disconnect them
// here so they can be used as normal digital i/o; they will be
// reconnected in Serial.begin()
#if defined(UCSRB)
UCSRB = 0;
#elif defined(UCSR0B)
UCSR0B = 0;
#endif
}
see next post...