diff options
| -rw-r--r-- | cores/arduino/wiring.c | 75 |
1 files changed, 37 insertions, 38 deletions
diff --git a/cores/arduino/wiring.c b/cores/arduino/wiring.c index 0cd25e5..6cb22c0 100644 --- a/cores/arduino/wiring.c +++ b/cores/arduino/wiring.c @@ -92,7 +92,6 @@ unsigned long micros() { #error TIMER 0 not defined #endif - #ifdef TIFR0 if ((TIFR0 & _BV(TOV0)) && (t < 255)) m++; @@ -122,8 +121,8 @@ void delay(unsigned long ms) /* Delay for the given number of microseconds. Assumes a 1, 8, 12, 16, 20 or 24 MHz clock. */ void delayMicroseconds(unsigned int us) { - // call = 4 cycles + 2 to 4 cycles to init us(2 for constant delay, 4 for variable) - + // call = 4 cycles + 2 to 4 cycles to init us(2 for constant delay, 4 for variable) + // calling avrlib's delay_us() function with low values (e.g. 1 or // 2 microseconds) gives delays longer than desired. //delay_us(us); @@ -131,7 +130,7 @@ void delayMicroseconds(unsigned int us) // for the 24 MHz clock for the aventurous ones, trying to overclock // zero delay fix - if (!us) return; // = 3 cycles, (4 when true) + if (!us) return; // = 3 cycles, (4 when true) // the following loop takes a 1/6 of a microsecond (4 cycles) // per iteration, so execute it six times for each microsecond of @@ -140,7 +139,7 @@ void delayMicroseconds(unsigned int us) // account for the time taken in the preceeding commands. // we just burned 22 (24) cycles above, remove 5, (5*4=20) - // us is at least 6 so we can substract 5 + // us is at least 6 so we can substract 5 us -= 5; //=2 cycles #elif F_CPU >= 20000000L @@ -153,7 +152,7 @@ void delayMicroseconds(unsigned int us) "nop" "\n\t" "nop" "\n\t" "nop"); //just waiting 4 cycles - if (us <= 1) return; // = 3 cycles, (4 when true) + if (us <= 1) return; // = 3 cycles, (4 when true) // the following loop takes a 1/5 of a microsecond (4 cycles) // per iteration, so execute it five times for each microsecond of @@ -162,7 +161,7 @@ void delayMicroseconds(unsigned int us) // account for the time taken in the preceeding commands. // we just burned 26 (28) cycles above, remove 7, (7*4=28) - // us is at least 10 so we can substract 7 + // us is at least 10 so we can substract 7 us -= 7; // 2 cycles #elif F_CPU >= 16000000L @@ -179,8 +178,8 @@ void delayMicroseconds(unsigned int us) // account for the time taken in the preceeding commands. // we just burned 19 (21) cycles above, remove 5, (5*4=20) - // us is at least 8 so we can substract 5 - us -= 5; // = 2 cycles, + // us is at least 8 so we can substract 5 + us -= 5; // = 2 cycles, #elif F_CPU >= 12000000L // for the 12 MHz clock if somebody is working with USB @@ -196,7 +195,7 @@ void delayMicroseconds(unsigned int us) // account for the time taken in the preceeding commands. // we just burned 20 (22) cycles above, remove 5, (5*4=20) - // us is at least 6 so we can substract 5 + // us is at least 6 so we can substract 5 us -= 5; //2 cycles #elif F_CPU >= 8000000L @@ -213,7 +212,7 @@ void delayMicroseconds(unsigned int us) // account for the time taken in the preceeding commands. // we just burned 17 (19) cycles above, remove 4, (4*4=16) - // us is at least 6 so we can substract 4 + // us is at least 6 so we can substract 4 us -= 4; // = 2 cycles #else @@ -227,7 +226,7 @@ void delayMicroseconds(unsigned int us) us -= 22; // = 2 cycles // the following loop takes 4 microseconds (4 cycles) // per iteration, so execute it us/4 times - // us is at least 4, divided by 4 gives us 1 (no zero delay bug) + // us is at least 4, divided by 4 gives us 1 (no zero delay bug) us >>= 2; // us div 4, = 4 cycles @@ -253,7 +252,7 @@ void init() #if defined(TCCR0A) && defined(WGM01) sbi(TCCR0A, WGM01); sbi(TCCR0A, WGM00); -#endif +#endif // set timer 0 prescale factor to 64 #if defined(__AVR_ATmega128__) @@ -357,31 +356,31 @@ void init() #if defined(ADCSRA) // set a2d prescaler so we are inside the desired 50-200 KHz range. - #if F_CPU >= 16000000 // 16 MHz / 128 = 125 KHz - sbi(ADCSRA, ADPS2); - sbi(ADCSRA, ADPS1); - sbi(ADCSRA, ADPS0); - #elif F_CPU >= 8000000 // 8 MHz / 64 = 125 KHz - sbi(ADCSRA, ADPS2); - sbi(ADCSRA, ADPS1); - cbi(ADCSRA, ADPS0); - #elif F_CPU >= 4000000 // 4 MHz / 32 = 125 KHz - sbi(ADCSRA, ADPS2); - cbi(ADCSRA, ADPS1); - sbi(ADCSRA, ADPS0); - #elif F_CPU >= 2000000 // 2 MHz / 16 = 125 KHz - sbi(ADCSRA, ADPS2); - cbi(ADCSRA, ADPS1); - cbi(ADCSRA, ADPS0); - #elif F_CPU >= 1000000 // 1 MHz / 8 = 125 KHz - cbi(ADCSRA, ADPS2); - sbi(ADCSRA, ADPS1); - sbi(ADCSRA, ADPS0); - #else // 128 kHz / 2 = 64 KHz -> This is the closest you can get, the prescaler is 2 - cbi(ADCSRA, ADPS2); - cbi(ADCSRA, ADPS1); - sbi(ADCSRA, ADPS0); - #endif + #if F_CPU >= 16000000 // 16 MHz / 128 = 125 KHz + sbi(ADCSRA, ADPS2); + sbi(ADCSRA, ADPS1); + sbi(ADCSRA, ADPS0); + #elif F_CPU >= 8000000 // 8 MHz / 64 = 125 KHz + sbi(ADCSRA, ADPS2); + sbi(ADCSRA, ADPS1); + cbi(ADCSRA, ADPS0); + #elif F_CPU >= 4000000 // 4 MHz / 32 = 125 KHz + sbi(ADCSRA, ADPS2); + cbi(ADCSRA, ADPS1); + sbi(ADCSRA, ADPS0); + #elif F_CPU >= 2000000 // 2 MHz / 16 = 125 KHz + sbi(ADCSRA, ADPS2); + cbi(ADCSRA, ADPS1); + cbi(ADCSRA, ADPS0); + #elif F_CPU >= 1000000 // 1 MHz / 8 = 125 KHz + cbi(ADCSRA, ADPS2); + sbi(ADCSRA, ADPS1); + sbi(ADCSRA, ADPS0); + #else // 128 kHz / 2 = 64 KHz -> This is the closest you can get, the prescaler is 2 + cbi(ADCSRA, ADPS2); + cbi(ADCSRA, ADPS1); + sbi(ADCSRA, ADPS0); + #endif // enable a2d conversions sbi(ADCSRA, ADEN); #endif |