UART interrupt handler

I presume you are talking about register values read from within the interrupt handler.

Within the exception handler the value of status will be 0 because its value has been zeroed by the exception. Its previous value is in estatus.

As for ipending, unfortunately there is a bug in version 1.0 of the Nios II kit which means that the debugger incorrectly displays ipending as zero when single stepping. This is fixed in 1.1.

To work around this you should set a breakpoint and continue - the correct value of ipending will be displayed.