STM32H743 FMC NOR hangs after repeated external resets

[tomercohenmunters]

My STM32H743 application runs from internal Flash, with some code and data in external NOR via FMC. It runs stably for days without NOR issues, but after repeated external resets the board eventually becomes silent and will not recover with an MCU reset; power-cycling restores it. HAL_NOR_Init() has writes disabled, and captured pre-FMC pin levels were unchanged. What should I check to identify whether FMC/NOR initialization, access sequencing, or reset behavior causes the hang?

[KDJEM.1]

Hello ​@tomercohenmunters and welcome to the community;

 

Is cache enabled?

Are you using the MPU?

Could you please check the reset pin

 

Thank you.

Kaouthar

[rich.g.williams]

​@tomercohenmunters 

The STM32H743 has about 1MB of internal RAM, can you run everything inside RAM as a test?

Are there enough wait states configured for your NOR memory?

Have you checked the coding that brings up the core voltage VOSA to its highest value assuming you are running at top speed?

Have you checked that the PLL’s are correctly configured?

It could be an external Xtal failing to restart? You could try using the internal HSI in place of external Xtal?

Are the power supplies clean and correct voltages? Is the reset signal clean and sharp?

Have you tried a second PCB in case of dry joint or similar PCB problem?

Is anything getting too hot?

A good idea would be to monitor the current to the MCU. When the MCU fails to start, if the current is too low suggests the sys clk didn’t restart - maybe a PLL cannot lock on again?

 

 

[Pavel A.]

It’s hard to tell without knowing your flash chip, but generally NOR flashes have certain state machine and spurious resets can get it in a weird state. In startup code (or bootloader) you can read the NOR flash status and detect if it needs additional reset actions before jumping to the main app.  The ST “HAL” library is generic and can miss some corner cases for specific chips . (this is similar to how I2C devices can get “locked up” and need additional reset).