<p><b>@maribu</b> commented on this pull request.</p>

<hr>

<p>In <a href="https://github.com/RIOT-OS/RIOT/pull/11438#discussion_r278185052">sys/include/barriers.h</a>:</p>
<pre style='color:#555'>> + * located at address `0x42` and we want to use that to measure the time a call
+ * to `void do_computing(void)` takes:
+ *
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ {.c}
+ * // BEWARE: This example deliberately contains **BUGS**
+ * #define TIMER    (*((uint16_t *)0x42))
+ *
+ * uint16_t measure_time(void) {
+ *     uint16_t pre = TIMER;
+ *     do_computing();
+ *     uint16_t post = TIMER;
+ *     return pre - post;
+ * }
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * In the above example from the compilers perspective the value in `TIMER`
</pre>
<p>I did. This is also the example presented here <a href="https://blog.regehr.org/archives/28" rel="nofollow">https://blog.regehr.org/archives/28</a>, or similar here <a href="https://hackaday.com/2015/08/18/embed-with-elliot-the-volatile-keyword/" rel="nofollow">https://hackaday.com/2015/08/18/embed-with-elliot-the-volatile-keyword/</a></p>

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