>SystemInit() configures the clock system and also configures an existing external memory controller.</li>
<li>SystemInit() must not use global variables.</li>
<li>SystemCoreClock is initialized with a correct predefined value.</li>
<li>Additional function void SystemCoreClockUpdate (void) is provided.</li>
<li>SystemCoreClockUpdate() updates the variable SystemCoreClock and must be called whenever the core clock is changed.</li>
<li>SystemCoreClockUpdate() evaluates the clock register settings and calculat