Re: Debugging in exception handlers

Hi,

Please, read exception chapter of the RCPU UM
for more details, especially 6.5.2.

THe main point is that the RCPU has only
one pair of the registers (SRR0/1) to save
the machine state and any break point is also
exception so if the processor gets an exception in an
exception handler before it saves SRR0/1, the machine
state will be lost
and there is no way to recover to the main code. 

The possibility of recovering from exception
is indicated by  the MSR[RI] bit, which is cleared any
time the RCPU gets exception.
Typical exception handler to be preemtive
needs to save the SRR0/SRR1 and set the MSR[RI] bit. 

By default the hardware breakpoints are not recognized
if the MSR[RI] bit is zero, that's why you can not get
the break point at address 0xc00, or trace it. 

To overcome this you may set LCTRL2[BRKNOMASK] bit,
but then you will not be able to return to your main
code automatically, and most likely will need to reset
the chip.

Hope this will help

Alex. 

--- prashanth_feb9 <[email protected]> wrote:

> Hi All,
>       I am working on Phycore MPC565 board with
> single step debugger.
> In the configuration file of single step the DER
> register value was
> 0x73e67c0f. Whenever an exception was generated the
> debugger used to
> display popup messages. To avoid the popup i have
> reset the bits in
> the DER register.
> 
> As an example, I have reset the system call
> exception bit in DER to
> check that whenever the exception occurs it branches
> to the exception
> handler (Address 0xC00)
> 
> But when I generate a system call exception using a
> sc instruction and
> apply a breakpoint at 0xC00 it does not stop at the
> breakpoint (This
> address is in the internal Flash).
> Please let me know why the breakpoint is not
> activated at 0xC00 and
> debug the exception handler code.
> 
> Thanks and Regards,
> Prashanth
> 
> 
> 
> 
> 
> 



		
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