Nios® V Processor Software Developer Handbook

ID 743810
Date 10/31/2022
Public

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6.7.3. Timestamp Driver

Sometimes you want to measure time intervals with a degree of accuracy greater than that provided by HAL system clock ticks. The HAL provides high resolution timing functions using a timestamp driver. A timestamp driver provides a monotonically increasing counter that you can sample to obtain timing information. The HAL only supports one timestamp driver in the system.

Specify a hardware timer peripheral as the timestamp device by manipulating BSP settings. The Intel-provided timestamp driver uses the timer that you specify.

If a timestamp driver is present, the following functions are available:

  • alt_timestamp_start()
  • alt_timestamp()

Calling alt_timestamp_start() starts the counter running. Subsequent calls to alt_timestamp() return the current value of the timestamp counter. Calling alt_timestamp_start() again resets the counter to zero. The behavior of the timestamp driver is undefined when the counter reaches (232 - 1 or 264 - 1, depending on the timer parametrization used).

You can obtain the rate at which the timestamp counter increments by calling the function alt_timestamp_freq(). This rate is typically the hardware frequency of the Nios® V processor system—usually millions of cycles per second. The timestamp drivers are defined in the alt_timestamp.h header file.

Using the Timestamp to Measure Code Execution Time

#include <stdio.h>

#include "sys/alt_timestamp.h"

#include "alt_types.h"

int main(void) {
  alt_u32 time1;
  alt_u32 time2;
  alt_u32 time3;
  if (alt_timestamp_start() < 0) {
    printf("No timestamp device available\n");
  } else {
    time1 = alt_timestamp();
    func1(); /* first function to monitor */
    time2 = alt_timestamp();
    func2(); /* second function to monitor */
    time3 = alt_timestamp();
    printf("time in func1 = %u ticks\n",
      (unsigned int)(time2 - time1));
    printf("time in func2 = %u ticks\n",
      (unsigned int)(time3 - time2));
    printf("Number of ticks per second = %u\n",
      (unsigned int) alt_timestamp_freq());
  }
  return 0;
}