Function linuxcnc_hal_sys::rtapi_get_clocks

pub unsafe extern "C" fn rtapi_get_clocks() -> c_longlong

rtapi_get_clocks returns the current time in CPU clocks. It is fast, since it just reads the TSC in the CPU instead of calling a kernel or RTOS function. Of course, times measured in CPU clocks are not as convenient, but for relative measurements this works fine. Its absolute value means nothing, but it is monotonically increasing* and can be used to schedule future events, or to time the duration of some activity. (* on SMP machines, the two TSC’s may get out of sync, so if a task reads the TSC, gets swapped to the other CPU, and reads again, the value may decrease. RTAPI tries to force all RT tasks to run on one CPU.) Returns a 64 bit value. The resolution of the returned value is one CPU clock, which is usually a few nanoseconds to a fraction of a nanosecond. May be called from init/cleanup code, and from within realtime tasks.

Note that longlong math may be poorly supported on some platforms, especially in kernel space. Also note that rtapi_print() will NOT print longlongs. Most time measurements are relative, and should be done like this: deltat = (long int)(end_time - start_time); where end_time and start_time are longlong values returned from rtapi_get_time, and deltat is an ordinary long int (32 bits). This will work for times up to a second or so, depending on the CPU clock frequency. It is best used for millisecond and microsecond scale measurements though.