diff options
Diffstat (limited to 'cores/arduino')
| -rwxr-xr-x | cores/arduino/wiring.c | 20 |
1 files changed, 19 insertions, 1 deletions
diff --git a/cores/arduino/wiring.c b/cores/arduino/wiring.c index bc01949..e7f7cde 100755 --- a/cores/arduino/wiring.c +++ b/cores/arduino/wiring.c @@ -124,8 +124,26 @@ 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 >= 20000000L + // for the 20 MHz clock on rare Arduino boards -#if F_CPU >= 16000000L + // for a one-microsecond delay, simply wait 2 cycle and return. The overhead + // of the function call yields a delay of exactly a one microsecond. + __asm__ __volatile__ ( + "nop" "\n\t" + "nop"); //just waiting 2 cycle + if (--us == 0) + return; + + // the following loop takes a 1/5 of a microsecond (4 cycles) + // per iteration, so execute it five times for each microsecond of + // delay requested. + us = (us<<2) + us; // x5 us + + // account for the time taken in the preceeding commands. + us -= 2; + +#elif F_CPU >= 16000000L // for the 16 MHz clock on most Arduino boards // for a one-microsecond delay, simply return. the overhead |