nanospin_calibrate()
Calibrate before calling nanospin*()
Synopsis:
#include <time.h>
int nanospin_calibrate( int disable );
Arguments:
- disable
- 1 to disable interrupts during the call to nanospin_calibrate(), or 0 to enable them; see below.
Library:
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
Description:
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.
Returns:
- EOK
- Success.
- EINTR
- A too-high rate of interrupts occurred during the calibration routine.
- EPERM
- The process doesn't have superuser capabilities.
Examples:
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. */
…
Classification:
| Safety: | |
|---|---|
| Cancellation point | No |
| Interrupt handler | No |
| Signal handler | Yes |
| Thread | Yes |