2011-02-26 06:50 PM
How to generate us and ms incremental counters?
2011-05-17 06:12 AM
Your question has no solution, if it's literally taken.
Even Arduino milli() or micro() functions use an interrupt routine... To make things clear, the following code is taken from: arduino-0022-src.tar.gz\arduino-0022\hardware\arduino\cores\arduino\wiring.c// 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; SIGNAL(TIMER0_OVF_vect) { // 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++; } 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()); } As you can see, the millis() and micros() functions use timer0_overflow_count and read the TIMER0 value. If you want to replicate them, TIM4 is alike Arduino's timer0. As regards your code, you have to follow what wiring.c does: handle TIM4 overflow interrupt and read TIM4 in millis() and micros() code. regards EtaPhi