Chapter 36 Nexus Development Interface (NDI)
MPC5602P Microcontroller Reference Manual, Rev. 4
Freescale Semiconductor
919
36.12.7 Methods of Entering Debug Mode
The OnCE Status Register indicates that the CPU has entered the debug mode via the DEBUG status bit.
The following sections describe how e200z0h Debug Mode is entered assuming the OnCE circuitry has
been enabled. e200z0h OnCE operation is enabled by the assertion of the
jd_en_once
input (see
36.12.7.1 External Debug Request During RESET
Holding the
jd_de_b
signal asserted during the assertion of
p_reset_b
, and continuing to hold it asserted
following the negation of
p_reset_b
causes the e200z0h core to enter Debug Mode. After receiving an
acknowledge via the OnCE Status Register DEBUG bit, the external command controller should negate
the
jd_de_b
signal before sending the first command. Note that in this case the e200z0h core does not
execute an instruction before entering Debug Mode, although the first instruction to be executed may be
fetched prior to entering Debug Mode.
In this case, all values in the debug scan chain will be undefined, and the external Debug Control Module
is responsible for proper initialization of the chain before debug mode is exited. In particular, the exception
processing associated with reset, may not be performed when the debug mode is exited, thus, the Debug
controller must initialize the PC, MSR, and IR to the image that the processor would have obtained in
performing reset exception processing, or must cause the appropriate reset to be re-asserted.
36.12.7.2 Debug Request During RESET
Asserting a debug request by setting the DR bit in the OCR during the assertion of
p_reset_b
causes the
chip to enter debug mode. In this case the chip may fetch the first instruction of the reset exception handler,
but does not execute an instruction before entering debug mode. In this case, all values in the debug scan
chain will be undefined, and the external Debug Control Module is responsible for proper initialization of
the chain before debug mode is exited. In particular, the exception processing associated with reset may
not be performed when the debug mode is exited, thus, the Debug controller must initialize the PC, MSR,
and IR to the image that the processor would have obtained in performing reset exception processing, or
must cause the appropriate reset to be re-asserted.
36.12.7.3 Debug Request During Normal Activity
Asserting a debug request by setting the DR bit in the OCR during normal chip activity causes the chip to
finish the execution of the current instruction and then enter the debug mode. Note that in this case the chip
completes the execution of the current instruction and stops after the newly fetched instruction enters the
CPU instruction register. This process is the same for any newly fetched instruction including instructions
fetched by the interrupt processing, or those that will be aborted by the interrupt processing.
36.12.7.4 Debug Request During Waiting, Halted or Stopped State
Asserting a debug request by setting the DR bit in the OCR when the chip is in the Waiting state
(
p_waiting
asserted), Halted state (
p_halted
asserted) or Stopped state (
p_stopped
asserted) causes the
7
CPU must be in debug mode with clocks running.