Due to a problem in the Quartus® II software version 15.1 and earlier, Nios® II Eclipse Debugger may give an error when Data Trigger is set to 0 with Hardware Breakpoints enabled in the Jtag Debug Tab in Nios II Gen 2 Processor. This error is seen with other memories except on-chip memory is used in the design.
Error: Target request failed: Warning: Cannot insert breakpoint. Cannot access memory at address 0x7c.
To work around this problem in the Quartus II software version 15.1 and earlier, follow the steps below:
1) Double click on Nios II Gen 2 Processor.
2) When the Parameter box appear, go to the Jtag Debug tab.
3) Set a value for Data Triggers. Hardware Breakpoints should already been enabled.
4) Generate Qsys and recompile Quartus.
This problem is scheduled to be fixed in a future version of the Quartus II software.