debugging timer interrupt

hi!!,
  I am using JTAGICE from Atmel with TinyOS. It uses
GDB along with JTAG interface to do on chip debugging.
With reference to it can you please answer my
following questions. 
** Only hardware breakpoint and hardware watch point
available in my case**

** The following problems arised as I need to debug a
program with timer interrupts handled in it**


#. How does the JTAG work? Does Jtag simply makes a
snapshot of the system when required, say for example
to view the stack at a breakpoint it just snaps the
stack and displays it and the original program
execution in the system is not halted. Or the
breakpoint means the program execution is halted and
then Jtag extracts information whichever required.

#. How the interrupts are handle by the JTAG? For
examle a timer fire interrupt. If a breakpoint is
included in the program then whether at the
break point the timer also stops Or the timer counts
and fires as without break point.

#. In continuity of above question what if we click
for next instruction? Then does it means next
instruction after breakpoint.Or the instruction
executing at that instant in the system if it was not
halted.

Regds...


		
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