nanospin_count()

Updated: May 06, 2022

Busy-wait without blocking for a number of iterations

Synopsis:

#include <time.h>

void nanospin_count( unsigned long count );

Arguments:

count
The number of iterations that you want to busy-wait for.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The nanospin_count() function busy-waits for the number of iterations specified in count. Use nanospin_ns_to_count() to turn a number of nanoseconds into an iteration count suitable for nanospin_count().

Note: The nanospin*() functions are designed for use with hardware that requires short time delays between accesses. You should use them to delay only for times less than a few milliseconds. For longer delays, use the POSIX timer_*() functions.

Examples:

Busy-wait for at least 100 nanoseconds:

#include <time.h>
#include <sys/syspage.h>

unsigned long time = 100;

…
/* Wake up the hardware, then wait for it to be ready. */

const unsigned long count = nanospin_ns_to_count( time );
if ( count != -1UL ) {
  nanospin_count( count );
} else {
  /* Check errno and handle error here somehow */
}

/* Use the hardware. */
…

Classification:

QNX Neutrino

Safety:  
Cancellation point No
Interrupt handler Yes
Signal handler Yes
Thread Yes

Caveats:

You should use busy-waiting only when absolutely necessary for accessing hardware.