What to Do When STM32F072CBT6 Goes Into Hard Fault Mode

What to Do When STM32F072CBT6 Goes Into Hard Fault Mode

What to Do When STM32F072CBT6 Goes Into Hard Fault Mode

1. Understanding Hard Fault Mode

A Hard Fault in STM32F072CBT6 refers to a critical error that prevents the system from continuing execution. This is a fault that occurs when the processor encounters an exception that it cannot recover from, such as Access ing invalid Memory , executing undefined instructions, or performing a privileged operation in an unprivileged mode.

When a Hard Fault occurs, the microcontroller will jump to a specific handler known as the Hard Fault Handler. In this mode, the program will stop, and the processor will store relevant state information to help identify the root cause of the error.

2. Common Causes of Hard Faults in STM32F072CBT6

Hard Faults can be caused by several factors, including:

Stack Overflow: This occurs when the stack pointer exceeds the available stack space, leading to corruption of memory. This is especially common in embedded systems with limited memory. Accessing Invalid Memory: If the code attempts to access an address that is outside of the valid memory range, such as an address that is not mapped or protected, a Hard Fault is triggered. Division by Zero: Attempting to divide a number by zero is an example of undefined behavior that can cause a Hard Fault. Executing Undefined Instructions: If the processor encounters an instruction that it doesn’t recognize, it will cause a Hard Fault. Privilege Violations: Trying to execute privileged instructions in an unprivileged mode (or vice versa) can result in a Hard Fault. Unaligned Memory Access: In some configurations, accessing data at an address that is not aligned according to the data type’s size can cause a Hard Fault. 3. Steps to Diagnose and Fix a Hard Fault

Here is a step-by-step approach to diagnose and fix the Hard Fault in STM32F072CBT6:

Step 1: Check the Hard Fault Handler

First, ensure that the Hard Fault handler is set up correctly. If it’s not already set up, you can write a Hard Fault handler in your code. Here’s a simple template for the handler:

void HardFault_Handler(void) { // Variables to store registers' values uint32_t stacked_r0; uint32_t stacked_r1; uint32_t stacked_r2; uint32_t stacked_r3; uint32_t stacked_r12; uint32_t stacked_lr; uint32_t stacked_pc; uint32_t stacked_xpsr; // Retrieve the saved registers from the stack __asm volatile( "TST lr, #4\n" // Test EXC_RETURN bit 2 "ITE EQ\n" // If Equal, branch to the next instruction "MRSEQ %0, MSP\n" // Main Stack Pointer "MRSNE %0, PSP\n" // Process Stack Pointer : "=r" (stacked_r0) ); // Further analysis of stacked registers // Use a debugger to inspect these values // stacked_r0, stacked_r1, stacked_r2, etc. represent the saved registers // stacked_pc will give you the program counter (PC) at the time of the fault // Debugging and breakpoint while (1); // Halt the system to analyze the fault }

In your debugger, inspect the program counter (stacked_pc) to see where the fault occurred. This will give you a clue about what part of the code triggered the Hard Fault.

Step 2: Use the Debugger to Identify the Fault Location

Once the Hard Fault handler is in place, connect the STM32F072CBT6 to a debugger (like ST-Link or J-Link). Set a breakpoint in the Hard Fault handler and examine the saved registers. Key values to inspect are:

PC (Program Counter): This will tell you where the program was executing when the fault occurred. LR (Link Register): This helps identify which return address was called. XPSR (Program Status Register): This contains the processor’s status at the time of the fault.

This information will allow you to narrow down the part of your program causing the fault.

Step 3: Check for Common Issues

Stack Overflow: Verify if you have allocated enough stack space for all the tasks or functions in your program. If the stack grows beyond its allocated space, it can overwrite memory and cause a Hard Fault. You can increase the stack size in your linker script. Memory Access: Check if your code is trying to access memory outside of valid ranges, such as peripheral addresses, or if you’re dereferencing null or invalid pointers. Unaligned Memory Access: Ensure that your data types are correctly aligned. For example, 32-bit values should be aligned to 4-byte boundaries. Division by Zero: Add checks in your code to ensure that no division by zero occurs.

Step 4: Use a System View for Analysis

Some IDEs (like STM32CubeIDE or Keil) provide a system view for analyzing stack usage, memory mapping, and peripheral states. This can give you an overview of where and why your system is encountering issues.

Step 5: Perform Test Cases and Stress Tests

After making potential fixes, run test cases and stress tests to reproduce the fault, ensuring that the issue is resolved. Monitor memory usage, peripheral initialization, and the execution flow during tests.

Step 6: Apply Protective Measures

To prevent future Hard Faults, consider the following measures:

Bounds Checking: Add checks before memory accesses or pointer dereferencing. Stack Guard: Implement a stack guard or watchdog to detect overflows. Error Handling: Ensure robust error handling and validation throughout the application. 4. Conclusion

A Hard Fault on STM32F072CBT6 can stem from stack overflows, invalid memory access, division by zero, unaligned memory access, or privileged instruction violations. Diagnosing the issue requires analyzing the fault through the Hard Fault handler, debugging the code, and checking for common issues such as memory management and pointer validity. With these steps, you can pinpoint and resolve the underlying cause of the Hard Fault and make your embedded system more robust and reliable.