Calibrate before calling nanospin*()
#include <time.h> int nanospin_calibrate( int disable );
- 1 to disable interrupts during the call to nanospin_calibrate(), or 0 to enable them; see below.
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The nanospin_calibrate() function performs the calibration for the nanospin()* family of delay functions. The first time that you call nanospin(), nanospin_ns(), or nanospin_ns_to_count(), the C library invokes nanospin_calibrate() with an argument of 0 (interrupts enabled), unless you call it directly first.
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.
Interrupts occurring during nanospin_calibrate() can throw off its timings. If disable is 0 (zero), you can prevent this situation by:
- letting the thread acquire I/O privilege
- disabling the interrupts around the nanospin_calibrate() call.
If disable is 1 (one), the code disables interrupts around the calibration loop(s). The calling thread is still responsible for obtaining I/O privilege before calling nanospin_calibrate().
In order to make startup faster and reduce jitter, nanospin_calibrate() tries to read the calibration data from values stored in the system page. The startup for some boards includes an -o option that you can use to specify the calibration data (100 loop time and overhead) to store in the system page.
- A too-high rate of interrupts occurred during the calibration routine.
- The process doesn't have superuser capabilities.
Busy-wait for 100 nanoseconds:
#include <time.h> #include <sys/syspage.h> int disable = 0; unsigned long time = 100; … /* Wake up the hardware, then wait for it to be ready. */ if ( (nanospin_calibrate( disable )) == EOK ) nanospin_count( nanospin_ns_to_count( time ) ); else printf ("Didn't calibrate successfully.\n"); /* Use the hardware. */ …