nanospin_ns_to_count()
QNX SDP8.0C Library ReferenceAPIDeveloper
Convert a time in nanoseconds into a number of iterations
Synopsis:
#include <time.h>
unsigned long nanospin_ns_to_count(
unsigned long nsec );
Arguments:
- nsec
- The number of nanoseconds that you want to convert.
Library:
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
Description:
The nanospin_ns_to_count() function converts the number of nanoseconds specified in nsec 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.
Returns:
The number of iterations to busy-wait for, or -1 if an error occurred (errno is set).
Errors:
- E2BIG
- The delay specified by nsec is greater than 500 milliseconds.
- ERANGE
- The frequency of ClockCycles() is greater than 36 GHz and would lead to issues with 64-bit math for larger spin times.
Examples:
Busy-wait for at least one nanosecond:
#include <time.h>
#include <sys/syspage.h>
unsigned long time = 1;
…
/* Wake up the hardware, then wait for it to be ready. */
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:
| Safety: | |
|---|---|
| Cancellation point | No |
| Signal handler | Yes |
| Thread | Yes |
Caveats:
You should use busy-waiting only when absolutely necessary for accessing hardware.
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