After re-programming STM32H7 device, I can’t connect to the device. Connect under reset doesn’t help. Why?
This is most probably related to power-supply configuration. STM32H7 devices with embedded step-down converter offer different power-supply schemes. The selected configuration depends on external components.
This configuration can be set only once after power-on reset. Choosing wrong configuration leads to MCU lock-up. The configuration is done with the following line in HAL library (usually placed in SystemClock_Config function):
Since the configuration can be changed only once after power-on reset, the issue might manifest itself after next power cycle.
Below is diagram from reference manual showing different hardware configurations for power supply.
The MCU contains protection mechanism that prevents setting higher voltage from internal SMPS to VCORE (1.8 or 2.5V). This should prevent damaging the MCU due to misconfiguration.
Solution 1 is to:
Other possibility is that the option bytes are configured in a way, that only Cortex-M4 boots after reset (BOOT_CM7/BCM7=0, BOOT_CM4/BCM4=1). Then you need to connect the debugger to Access port 3 (Cortex-M4), instead of Access port 0 (Cortex-M7).
In current STM32CubeProgrammer version (2.2.0 and older) this seems to not work. Please use ST-Link Utility instead, or update STM32CubeProgrammer (when new version is available).
For development it is recommended to keep booting from both cores enabled, otherwise some tools/IDEs might not be able to work with the device.
There are two possible root causes, that can cause this issue. First one is more probable and is related to power supply misconfiguration. And second to configuration of boot process in option bytes.
Possible root cause 1 (power supply misconfiguration)
This applies to all STM32H7 devices with configurable internal SMPS step-down.This is most probably related to power-supply configuration. STM32H7 devices with embedded step-down converter offer different power-supply schemes. The selected configuration depends on external components.
This configuration can be set only once after power-on reset. Choosing wrong configuration leads to MCU lock-up. The configuration is done with the following line in HAL library (usually placed in SystemClock_Config function):
HAL_PWREx_ConfigSupply(...);Most of the boards have the supply directly from SMPS (if available in MCU), which requires the above function to be called with PWR_DIRECT_SMPS_SUPPLY parameter. But STM32CubeMX generated projects might have PWR_LDO_SUPPLY option by default. Also the PWR_DIRECT_SMPS_SUPPLY option is available in version 5.4.0 and older.
Since the configuration can be changed only once after power-on reset, the issue might manifest itself after next power cycle.
Below is diagram from reference manual showing different hardware configurations for power supply.
The MCU contains protection mechanism that prevents setting higher voltage from internal SMPS to VCORE (1.8 or 2.5V). This should prevent damaging the MCU due to misconfiguration.
Solution
Since the power-supply is usually configured immediately after reset, it is difficult to connect during that short window.Solution 1 is to:
- Plug the board to power supply, while the reset button is being held low (or NRST pin in general).
- Keep the reset button low.
- Connect via STM32CubeProgrammer. When the program starts connecting, release the reset button. Although this requires quite precise timing, it should be easy to achieve.
- Perform mass erase.
- Make sure that you fixed the power-supply configuration in your project.
- Plug the board to power supply, while the BOOT0 pin is being held high. This requires the BOOT_CM7_ADD1 to be set to system memory.
- Keep the BOOT0 button high.
- Connect via STM32CubeProgrammer. The system bootloader shouldn’t touch the power-supply configuration. However it will configure the pins related to bootloader communication interfaces and might disturb external components on the board (this might be critical for custom PCBs).
- Perform mass erase.
- Make sure that you fixed the power-supply configuration in your project.
Possible root cause 2 (Cortex-M7 boot disabled)
This applies to all STM32H7 devices with dual-core feature.Other possibility is that the option bytes are configured in a way, that only Cortex-M4 boots after reset (BOOT_CM7/BCM7=0, BOOT_CM4/BCM4=1). Then you need to connect the debugger to Access port 3 (Cortex-M4), instead of Access port 0 (Cortex-M7).
In current STM32CubeProgrammer version (2.2.0 and older) this seems to not work. Please use ST-Link Utility instead, or update STM32CubeProgrammer (when new version is available).
For development it is recommended to keep booting from both cores enabled, otherwise some tools/IDEs might not be able to work with the device.
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