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POC++/POSIX how to get a millisecond time-stamp the most efficient way?
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  1. POC++/POSIX how to get a millisecond time-stamp the most efficient way?
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    copied!<p>I'm using a open-source library for i2c bus actions. This library frequently uses a function to obtain an actual time-stamp with millisecond resolution. </p> <p>Example Call:</p> <pre><code>nowtime = timer_nowtime(); while ((i2c_CheckBit(dev) == true) &amp;&amp; ((timer_nowtime() - nowtime) &lt; I2C_TIMEOUT)); </code></pre> <p>The application using this i2c library uses a lot of CPU capacity. I figured out, that the running program the most time is calling the function <code>timer_nowtime()</code>.</p> <p>The original function: </p> <pre><code>unsigned long timer_nowtime(void) { static bool usetimer = false; static unsigned long long inittime; struct tms cputime; if (usetimer == false) { inittime = (unsigned long long)times(&amp;cputime); usetimer = true; } return (unsigned long)((times(&amp;cputime) - inittime)*1000UL/sysconf(_SC_CLK_TCK)); } </code></pre> <p>My aim now is, to improve the efficiency of this function. I tried it this way:</p> <pre><code>struct timespec systemtime; clock_gettime(CLOCK_REALTIME, &amp;systemtime); //convert the to milliseconds timestamp // incorrect way, because (1 / 1000000UL) always returns 0 -&gt; thanks Pace //return (unsigned long) ( (systemtime.tv_sec * 1000UL) + (systemtime.tv_nsec // * (1 / 1000000UL))); return (unsigned long) ((systemtime.tv_sec * 1000UL) + (systemtime.tv_nsec / 1000000UL)); </code></pre> <p>Unfortunately, I can't declare this function <em>inline</em> (no clue why). </p> <p>Which way is more efficient to obtain an actual timestamp with ms resolution? I'm sure there is a more per-formant way to do so. Any suggestions? </p> <p>thanks. </p>
 

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