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Code Issues Releases Activity

Improved accuracy of delayMicroseconds().

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This commit is contained in:
David A. Mellis 2005-12-03 17:03:26 +00:00
parent 9e43fe9d4c
commit bbec45d3df
3 changed files with 37 additions and 5 deletions
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1
readme.txt
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@ -25,6 +25,7 @@ order to read the same physical pin.
Now flushing the serial port before uploading (should fix some errors). Now flushing the serial port before uploading (should fix some errors).
Added a printNewline() function. Added a printNewline() function.
Updated icon of the Windows executable. Updated icon of the Windows executable.
Improved accuracy of the delayMicroseconds() function.
0002 - 2005.10.05 0002 - 2005.10.05
New build process no longer uses makefiles; now controlled by preferences.txt. New build process no longer uses makefiles; now controlled by preferences.txt.

37
targets/arduino/wiring.c
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@ -19,7 +19,7 @@
Free Software Foundation, Inc., 59 Temple Place, Suite 330, Free Software Foundation, Inc., 59 Temple Place, Suite 330,
Boston, MA 02111-1307 USA Boston, MA 02111-1307 USA
$Id: wiring.c,v 1.7 2005/05/28 21:04:15 mellis Exp $ $Id$
*/ */
#include <avr/io.h> #include <avr/io.h>
@ -292,9 +292,40 @@ void delay(unsigned long ms)
timerPause(ms); timerPause(ms);
} }
void delayMicroseconds(unsigned long us) /* Delay for the given number of microseconds. Assumes a 16 MHz clock.
* Disables interrupts, which will disrupt the millis() function if used
* too frequently. */
void delayMicroseconds(unsigned int us)
{ {
delay_us(us); // calling avrlib's delay_us() function with low values (e.g. 1 or
// 2 microseconds) gives delays longer than desired.
//delay_us(us);
// 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;
// disable interrupts, otherwise the timer 0 overflow interrupt that
// tracks milliseconds will make us delay longer than we want.
cli();
// busy wait
__asm__ __volatile__ (
"1: sbiw %0,1" "\n\t" // 2 cycles
"brne 1b" : "=w" (us) : "0" (us) // 2 cycles
);
// reenable interrupts.
sei();
} }
int main(void) int main(void)

4
targets/arduino/wiring.h
View File

@ -19,7 +19,7 @@
Free Software Foundation, Inc., 59 Temple Place, Suite 330, Free Software Foundation, Inc., 59 Temple Place, Suite 330,
Boston, MA 02111-1307 USA Boston, MA 02111-1307 USA
$Id: wiring.h,v 1.4 2005/05/24 17:47:41 mellis Exp $ $Id$
*/ */
#ifndef Wiring_h #ifndef Wiring_h
@ -57,7 +57,7 @@ typedef uint8_t byte;
void delay(unsigned long); void delay(unsigned long);
void delay_ms(unsigned short ms); void delay_ms(unsigned short ms);
void delayMicroseconds(unsigned long us); void delayMicroseconds(unsigned int us);
void pinMode(int, int); void pinMode(int, int);
void digitalWrite(int, int); void digitalWrite(int, int);
int digitalRead(int); int digitalRead(int);