Fixing delayMicroseconds() timing for 20 MHz clocks. (Erdem U. Altinyurt)
http://code.google.com/p/arduino/issues/detail?id=306
This commit is contained in:
parent
59a3690eb4
commit
aae9972a2b
|
@ -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
|
||||
|
|
Loading…
Reference in New Issue