The answer to this question varies depending on your system configuration.
One way of finding out the cause of a malfunction is by using test tools.
The following shows an example of the procedure for malfunction analysis.
1) Set a breakpoint at the point where the malfunction occurred.
2) Execute the program to verify whether the execution results (trace data) match the expected values.
3) Verify whether the input/output values up to the breakpoint match the expected values.
4) If no problem is found in the above steps 2) and 3), the malfunction may have been caused by hardware. In this case, use test tools to directly control SFRs, etc. and verify hardware operation.
It is also possible to analyze a malfunction by preparing a simplified version of the program and verifying program operation.