In this lesson, you will learn how to intercept hardware errors by redirecting the processor to your own custom code whenever a fault occurs.
The Danger of an Undefined State
When a microcontroller encounters a critical hardware error—like attempting to access an invalid memory address or executing an undefined instruction—it enters a "Fault." By default, many microcontrollers will either hang in an infinite loop or reset unpredictably. This is dangerous because the system loses its internal state, making it impossible to know why the failure happened.
Vector Redirection
Recall that your system uses a Vector Table—a list of memory addresses pointing to where the processor should jump when specific events occur. To handle faults, we modify this table to point to our own custom functions, called Exception Handlers, instead of the default hardware behavior.
By "redirecting" the vector, you take control of the CPU the moment a failure occurs. This allows you to perform "post-mortem" debugging, such as logging the fault type, saving the CPU registers to RAM, or safely shutting down peripherals to prevent physical damage.
Implementing a Fault Handler
To implement this, you declare a function with a specific name that the linker maps to your vector table (often marked with a special attribute or placed in a specific memory section).
// A simple HardFault handler that stops the system safely
void HardFault_Handler(void) {
// 1. Log or store error status to a known memory location
// 2. Disable system outputs to ensure safety
while(1) {
// Infinite loop to prevent the CPU from executing
// random instructions after the fault
}
}
By defining this function, you ensure that even when the hardware fails, the processor doesn't wander off into "undefined space." Instead, it is forced into your handler, where you can implement a controlled recovery sequence or signal a diagnostic LED. This keeps your system predictable, even when the software crashes.
Key Takeaway: Vector redirection allows you to catch hardware faults by overriding default system behavior, enabling graceful error management and easier debugging instead of letting the system drift into an undefined state.