Understanding the Problem
Interrupt handler issues in firmware can arise from various factors ranging from incorrect vector table setup to improper handling within the interrupt service routine (ISR). The ARM Compiler, like any toolchain, can have quirks that require attention to detail. Below are strategies to address these issues effectively.
Check the Vector Table
- Ensure that the vector table is correctly defined and located at the correct memory address. The ARM Cortex-M architecture expects the vector table to start at location
0x0000_0000 by default.
__attribute__((section(".isr_vector")))
const void* vector_table[] = {
(void*) &__stack, // Initial Stack Pointer
Reset_Handler, // Reset Handler
NMI_Handler, // NMI Handler
HardFault_Handler, // Hard Fault Handler
// Other exception vectors...
};
- Make sure the vector table is placed in the correct section in your linker script, often named
.isr_vector or .vectors.
Correct Exception Handling
- Ensure that each interrupt handler is correctly implemented and registered. Handlers should be declared with the
void return type and no parameters.
void TIM2_IRQHandler(void) {
if(TIM2->SR & TIM_SR_UIF) {
// Clear update interrupt flag
TIM2->SR &= ~TIM_SR_UIF;
// Handle the interrupt event
}
}
- Make sure each ISR clears its interrupt flag. Failing to do so may result in the continuous triggering of the interrupt.
Linker Configuration
- Check the linker script for the correct memory mappings and ensure that the
.isr_vector section is marked with the appropriate attributes to be placed at the start of flash memory.
SECTIONS {
.isr_vector : {
KEEP(*(.isr_vector))
} > FLASH
}
Compiler Optimization Issues
- Sometimes, high levels of optimization can lead to interrupts being mishandled. Test your firmware with different compiler optimization levels.
armcc -O0 main.c -o main.o
- Use
-O0 or -Og for debugging to ensure that optimization isn't stripping essential interrupt-handling code.
Verify with Debugging Tools
Use debugging tools like ARM Coresight for detailed inspection. Debugging allows you to single-step through your code and observe the behavior of your ISRs in real-time.
Pay attention to NVIC registers to ensure interrupts are enabled and properly configured.
Stable Stack and Heap Management
- Interrupt routines run on the process stack; ensure the stack is sufficiently large to handle ISR requirements without overflow.
_stack_size = 0x1000; /* 4KB stack size */
_heap_size = 0x1000; /* 4KB heap size */
Conclusion
Addressing interrupt handler issues often involves examining multiple facets of the firmware's architecture and configuration. With careful attention to vector setup, ISR handling, memory mapping, and compiler behavior, you can resolve most issues related to interrupts in firmware compiled with the ARM Compiler. Always conduct thorough testing and use debugging tools to validate your approach.
