Why does my NMI handler address end with a 0, but the vector address ends with a 1?
Happy Sunday guys, I am working with an STM32-F49ZI Nucleo board, which features an ARM Cortex-M4 32-bit MCU. I am using GCC as my compiler and GCC linker.
For debugging, I am using OpenOCD and I inspected the addresses through the memory window in the debugger
I have written my own NMI handler function,
Here's the handler code:
For instance, the debugger shows the following:
-
- NMI vector address:
Could you explain why there is a discrepancy between these addresses and how the ARM Cortex-M architecture influences this behavior?"
For debugging, I am using OpenOCD and I inspected the addresses through the memory window in the debugger
I have written my own NMI handler function,
NMI_HandlerHere's the handler code:
For instance, the debugger shows the following:
-
NMI_Handler0x8010 1000- NMI vector address:
0x8010 1001Could you explain why there is a discrepancy between these addresses and how the ARM Cortex-M architecture influences this behavior?"
Solution
The last bit of the vector address is set to 1 to indicate that the handler uses Thumb instructions. When the processor jumps to the handler, it automatically clears this bit to get the actual function address, Cortex-M processors always operate in Thumb mode.
