Solved
The code I wrote on the board Nucleo-L522ZE-Q has time interruption and controls the LED to flash. It is successful. After being applied to my own circuit board by ST-LINK , the time interruption cannot occur. I want to know why?
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Ok, and what have you learned in the debugger, having stepped in from Reset_Handler ?
Check your design for BOOT0 pin/settings.
Check your HSE clock source is present and starts properly.
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