Specifications

Note: An exception handler must never execute an unimplemented instruction. The HAL exception
handling system does not support nested software exceptions.
Figure 8-2: HAL Software Exception Funnel Including the Optional Instruction Emulation
Logic
Exception at
unimplemented
instruction?
Exception
at trap
instruction
Yes
Enter
Exit
No
Emulate
unimplemented
instruction
Optional
Unimplemented
Instruction
Logic
No
Infinite
loop
Break
Optional
Trap Logic
Yes
Instruction-
related
exception handler
registered?
No
Yes
Instruction-
related
exception
handler
Instruction-Related Exceptions
If the cause of the software exception is not an unimplemented instruction, the HAL software exception
funnel checks for a registered instruction-related exception handler. If no instruction-related exception
handler is registered, the exception is handled.
For more information, refer to the “Software Trap Handling” chapter. If a handler is registered, the HAL
software exception funnel calls it, then restores context and returns.
8-30
Instruction-Related Exceptions
NII5V2
2015.05.14
Altera Corporation
Exception Handling
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