Posted on June 08, 2017 at 21:15>>I suspect there may be some silicon bug with STM32F4 series chip.
These chips are well validated, significantly better than most custom designs. Unless you can demonstrate the same failure on a DISCO/NUCLEO board assume the failure is in your design, not theirs.
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No help from ST
This is primarily a *user* forum, if you want support from ST you should go through your account manager, or FAE.
>>I was wondering why Segger has STM32 specific unlock utility?! Is this very common problem with STM32?
Because there are valid reasons to lock the parts, most commercial uses lock down the chips to prevent IP theft or make it more difficult. It is often a programming step, especially in production. These same people frequently don't have the skills, or provision within their own code, to unlock the parts themselves.
We don't seem to be awash with the issue here, we get people occasionally who lock their devices on purpose but without the knowledge to recover them. ie stuck their fingers in a chinese trap before understanding how to get out.
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So there are other unknown power supply related situations when the chip can go into this mode.
FLASH use a charge-pump circuit to generate programming voltages and needs a power supply that meets specification to function correctly. Timing is also critical.
