Posted on July 07, 2013 at 23:48Going through trying to figure out if there is actually a way to make this run at 168Mhz or if that is a chip spec and not the EVAL board spec? The code seems to assume its running that fast which is confusing me.
You have to change it!
Of course it can run at 168 MHz, you just have to change the 25 divider that assumes an external 25 MHz source of the EVAL series boards to 8 to reflect that fact that the external clock on the STM32F4-Discovery board is 8 MHz. If I recall the part will take an external input between 4 and 26 MHz. The software has to be cognizant of these settings because it's can't figure them out by itself. The PLL requires you to have the comparison frequency between 1-2 MHz. You can play games with the settings to get the processor to run at a desired frequency, 168 MHz may not be ideal for generating other timing values that might be needed for external devices.
You also need to make sure the define HSE_VALUE is 8000000, again to reflect the reality of the system you're using. This value is used in math for computing things like baud rates.
There is actually a firmware library and examples tailored to the STM32F4-Discovery, the primary firmware/dsp library is tailored to the EVAL boards, and F4 parts in general.
