Get or set a clock period
#include <sys/neutrino.h> int ClockPeriod( clockid_t id, const struct _clockperiod * new, struct _clockperiod * old, int reserved ); int ClockPeriod_r( clockid_t id, const struct _clockperiod * new, struct _clockperiod * old, int reserved );
Use the -l c option to qcc to link against this library. This library is usually included automatically.
You can use the ClockPeriod() and ClockPeriod_r() kernel calls to get or set the clock period of the clock.
|If you want to get the clock period, consider calling clock_getres() instead of using these kernel calls directly.|
These functions are identical except in the way they indicate errors. See the Returns section for details.
All the timer_*() calls operate with an accuracy no better than the clock period. Every moment within the Neutrino microkernel is referred to as a tick. A tick's initial length is determined by the clock rate of your processor:
|CPU clock speed:||Default value:|
|≥ 40MHz||1 millisecond|
|< 40MHz||10 milliseconds|
Since a very small tick size imposes an interrupt load on the system, and can consume all available processor cycles, the kernel call limits how small a period can be specified. The lowest clock period that can currently be set on any machine is 10 microseconds.
If an attempt is made to set a value that the kernel believes to be unsafe, the call fails with an EINVAL. The timeslice rate (for “round-robin” and “other” scheduling policies) is always four times the clock period (this isn't changeable).
These calls don't block.
The only difference between these functions is the way they indicate errors:
Clocks, Timers, and Getting a Kick Every So Often chapter of Getting Started with QNX Neutrino