Tutorial: Switching clock modes with the FRDM KL25z in mbed

Ever since I got a hold of my FRDM-KL25Z board I fell in love with it. It has the convience of running straight from either the built in SDA USB connector, an external 5-9 volts supply or a regulated 3.3v supply. It boasts USB host, ultra low power modes, and when paired with the mbed online compilation polatform it essentially erased all my worries about working in several computers and file revisions. Once you use the mercurial based repository you will wonder why you ever did any project differently before. And it costs around 15.00 USD, so its a hard price break to beat for homegrown projects.

That being said, there are several disadvantages. Since you have to rely on the mbed library for mostly everything, some rather crucial functions are still not implemented, or probably fall outside the scope of the core mbed library. One of such functions is clock control. On the KL25z there is simply no way of switching the clock mode either than manually coding it. In this tutorial I will go through the steps of controlling the Multipurpose Clock Generator (MCG), or you can just skip the tutorial and get the library:


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