Posted on January 15, 2015 at 00:58May be you're just been lucky? The speed the flash can operate at depends on IC fabrication process variations, operational voltage and temperature, typically you'd need to add one wait state for each 24 MHz of speed increase. Other parts of the design might have critical paths, also limiting speed.
If clocks don't start it's indicative of component issues, the oscillator has expectations about circuit characteristics, the crystal's load capacitance, cut, series/parallel resistance, and decoupling capacitors, etc. ST has an application note, and BOM examples, to design a circuit that will operate correctly over temperature, voltage, etc.
The part will always start with the HSI. If the HSE doesn't start or the PLL doesn't lock you'd need to review the error handling of that code, this is YOUR job as a developer, ST's code is a rough outline and will often enter infinite loops in error conditions. You might want to do other things.
It also sets the PLL and Flash wait states based on expectations of what frequency is being supplied. If YOU change that, YOU need to adapt your code to address those changes, and validate it to your own satisfaction. If the timing is wrong the chip might crash, or malfunction, or you could just end up in the Hard Fault Handler. If you haven't replaced the while(1) in the Hard Fault Handler with some useful diagnostic code you might want to consider that too.
So it's really YOUR responsibility to correctly select parts, adapt the code behaviour, and validate your design.
