Simulate STM32F4 brownout reset using STM32F100
I see no major flaw in this design, but consider few limitations:


as this is software based brownout reset (not configured in option bytes), it will not work until your code configures it (so voltage drop just after power up will be undetected),
as it uses interrupt it will not work if interrupt with higher or equal interrupt priority is already executing.


As far is I know reset flags must be cleared manually (at least in F4), so:


brownout will not wipe software reset flag,
you must clear this flag on startup, otherwise after other reset you can have multiple flags.