What can stop the debugger getting control of the NIOS II?

[Altera_Forum]

Hi, 

 I'm using the NIOS II 9.1sp2 SBT environment. Occasionally during debugging I get an error from the debugger when I try to pause the program - "Processor failed to go into debug mode".  Does anybody know what target conditions can stop the debugger from gaining control of the NIOS II target?  Thanks, Darren.

[Altera_Forum]

When I have seen this, it has been because my code had memory write errors or I misprogrammed DMA and either case hit memory used by the jtag debugger part of system. Sometimes when you blow away memory the debugger disconnects immediately. I think in your case it's already dead and it doesn't know it until you tell it to pause execution. 

 If the program is too simple and you're sure it cannot be this, then it could be your DRAM controller is not set up right or you have DRAM that is misbehaving.  Bill

[Altera_Forum]

Thanks Bill. In my case it was a hardware issue that stopped a H/W register read access from completing - locking up the bus. 

 Can't blame the NIOS for that one...