Why does downloading ELF file into Nios® V/g processor fail when disabled branch prediction, while enabled instruction cache?

Description

Due to a problem in the Quartus^® Prime Pro Edition Software version 25.3.1, downloading ELF file into Nios^® V/g processor might fail when both the conditions below are fulfilled.  

• Branch prediction is disabled, and

• Instruction cache is enabled  

The niosv-download command returns the error message below. 

Unexpected vCont reply in non-stop mode: E30  ERROR: GDB failed. 

This is because there is an RTL bug in the instruction cache related to its reset state. 

Resolution

To work around this problem in the Quartus^® Prime Pro Edition Software version 25.3.1, 

• Either enable branch prediction, 

• Or disable instruction cache 

This problem is scheduled to be fixed in a future release of the Quartus^® Prime Pro Edition Software version 26.1.