Why are the peripherals under 2GB Peripheral Region still cached by the Nios® V/g processor?

Description

Due to a problem in the:

• Quartus® Prime Pro Edition Software version 23.1, 23.2, 23.3, 23.4, 24.1, 24.2, 24.3, 24.3.1, 25.1
• Quartus® Prime Standard Edition Software version 23.1, 24.1

The Nios® V/g processor still caches the peripherals if they are placed under a Peripheral Region that is configured to 2GB, regardless of the Base Address.

This is due to a problem in the processor RTL failing to correctly implement the 2GB Peripheral Region.

Other Peripheral Region sizes are not affected; only 2GB is affected.

Resolution

To work around this problem, please select other Peripheral Region sizes except 2GB. The Nios® V/g processor still offers Peripheral Region sizes ranging from 64KB to 1GB.

The 2GB Size option for Nios® V/g processor Peripheral Region is removed beginning with the Quartus® Prime Pro Edition Software version 25.1.1 and Quartus® Prime Standard Edition Software version 25.1.