Why does the Nios® V/g processor become unstable when both CLIC and shadow registers are enabled?

Description

Due to a problem in the Quartus® Pro/Standard Edition software version 26.1/25.1, Nios® V/g interrupt handling might be unstable when both CLIC mode and Shadow Register are enabled.

This is because the Shadow Register CSR (msrfstatus) is not saved/restored during interrupt context saving under CLIC mode.

Resolution

To work around this problem in the Quartus® Prime Pro/Standard Edition Software version 26.1/25.1, follow these steps:

1. Download the machine_trap.zip
2. Extract to get the new machine_trap.S
3. Search for the old machine_trap.S in your BSP project
4. Replace with the new machine_trap.S file
5. Rebuild your software

Additional Information

This problem is currently scheduled to be resolved in a future release of the Quartus® Prime Pro and Standard Edition Software.