I've just started working with the Stellaris LM3S9B92 (Cortex M3). I have some problems understanding the
SysCtlClockSet() function. On the Driverlib page 350 they say that:
The use of the PLL is chosen with either SYSCTL_USE_PLL or SYSCTL_USE_OSC.
and after that, to use an external source I should use:
SYSCTL_USE_OSC | SYSCTL_OSC_MAIN. and for the PLL use SYSCTL_USE_PLL | SYSCTL_OSC_MAIN,
My question is, what's the difference between
SYSCTL_USE_PLL? I found this example on the net, and the person is using both an external clock source and the PLL! What is considered as a clock source and what is ignored?