Why STM32L072CBT6 Freezes After Flashing and How to Resolve It

Why STM32L072CBT6 Freezes After Flashing and How to Resolve It

Introduction: The STM32L072CBT6 microcontroller, part of STMicroelectronics' STM32L0 series, is a low- Power , high-performance MCU. However, sometimes users may encounter an issue where the device freezes after flashing the firmware. This could cause the system to become unresponsive or even halt unexpectedly, impacting the functionality of embedded systems. Let’s analyze the possible causes and provide a step-by-step solution to resolve the issue.

Possible Causes of the Freeze:

Incorrect Flashing Procedure: If the flashing process is not done correctly, the MCU might freeze due to incomplete or corrupted firmware. This can happen if there are interruptions during the flashing or if the wrong configuration is selected. Bootloader Issues: The STM32L072CBT6 might be stuck in a bootloader or in an incorrect boot mode (e.g., System Bootloader or UART Bootloader). If the MCU is trying to boot from an invalid Memory region, it could result in freezing. Power Supply Instability: Unstable or insufficient power to the MCU can cause the system to behave unpredictably after flashing. If the voltage is too low or fluctuates, the device may freeze or fail to start. Watchdog Timer Not Properly Handled: The Watchdog Timer (WDT) is a hardware feature designed to reset the MCU if it stops executing code as expected. If your firmware doesn't properly reset or disable the watchdog, the MCU might reset or freeze due to the watchdog timing out. Faulty Peripherals Initialization: If peripherals like GPIOs, UART, I2C, etc., are not correctly initialized, they may cause the MCU to hang during boot-up after flashing the firmware. Memory Issues (Stack/Heap Overflow): If the firmware uses too much stack or heap memory, or if there are memory allocation issues, it can cause the MCU to crash or freeze during runtime. Incompatible or Incorrect Compiler Settings: Incorrect compiler settings, such as wrong optimization levels or incorrect memory allocation, could cause the firmware to behave erratically or crash after being flashed.

Step-by-Step Solution to Resolve the Freeze:

Step 1: Verify Flashing Procedure

Ensure that the flashing procedure is being done correctly. Double-check that you're using the right programming tool (e.g., ST-Link, J-Link) and ensure the firmware is compatible with the STM32L072CBT6. Reflash the MCU with the correct firmware and make sure no interruptions occur during the process. If possible, verify that the entire flash memory is written correctly.

Step 2: Check Bootloader and Boot Configuration

The STM32L072CBT6 might have been left in bootloader mode. To ensure the MCU is starting from the correct memory location: Check the Boot0 and Boot1 pins on the MCU. Set Boot0 to 0 (select main flash memory) and Boot1 to 0 (select user flash). If using a bootloader, ensure that the bootloader firmware is correctly configured and that it doesn't conflict with your application code.

Step 3: Inspect Power Supply

Verify that the power supply to the MCU is stable and within the required range (typically 1.7V to 3.6V for STM32L072CBT6). Check for voltage fluctuations, as these can cause the MCU to freeze. If necessary, use a decoupling capacitor close to the power pins of the MCU to stabilize the voltage.

Step 4: Watchdog Timer Handling

Ensure that the watchdog timer is either properly managed in the code (reset it when needed) or disabled if you are not using it. To disable the watchdog timer, you can modify the firmware to disable the Independent Watchdog (IWDG) or the Window Watchdog (WWDG) during initialization if they are not being used.

Step 5: Ensure Proper Peripheral Initialization

Make sure that all required peripherals (UART, I2C, GPIO, etc.) are correctly initialized before use. Check the initialization sequence of the peripherals in your code. Sometimes improper configuration (e.g., setting incorrect GPIO modes) can cause the MCU to freeze.

Step 6: Debug and Inspect Memory Usage

Use debugging tools like STM32CubeIDE or a debugger (ST-Link, J-Link) to monitor memory usage, and check for potential stack or heap overflows. Optimize your code to ensure that the MCU’s available memory is not being exhausted. Use memory protection features or change the memory configuration if needed.

Step 7: Verify Compiler Settings

Ensure that your compiler settings match the target device specifications (STM32L072CBT6). Make sure that you are not using overly aggressive optimization levels which might cause issues during runtime. Rebuild your project with different optimization levels or debug settings to see if the issue resolves.

Step 8: Use Debugging Tools

If the device is still freezing, consider using an in-circuit debugger to step through your code and see where it halts. You can also use serial prints or logging to detect the specific point where the MCU freezes, which may help identify which part of the code or peripheral initialization is causing the issue.

Conclusion: Freezing issues in the STM32L072CBT6 after flashing are commonly caused by incorrect flashing procedures, bootloader problems, unstable power, or improper handling of the watchdog timer and peripherals. By following the above steps, you should be able to diagnose and resolve the problem efficiently. Always ensure your hardware is correctly powered, your firmware is properly flashed, and that your code handles all system initialization and memory allocation correctly.