Chapter 27 Functional Safety
MPC5602P Microcontroller Reference Manual, Rev. 4
752
Freescale Semiconductor
7. Any write operation in any access mode to area #3 while Hard Lock Bit GCR[HLB] is set
27.2.7
Reset
The reset state of each individual bit is shown in
Section 27.2.5.2, “Registers description.
In summary,
after reset, locking for all MR
n
registers is disabled. The registers can be accessed in Supervisor Mode
only.
27.3
Software Watchdog Timer (SWT)
27.3.1
Overview
The Software Watchdog Timer (SWT) is a peripheral module that can prevent system lockup in situations
such as software getting trapped in a loop or if a bus transaction fails to terminate. When enabled, the SWT
requires periodic execution of a watchdog servicing sequence. Writing the sequence resets the timer to a
specified time-out period. If this servicing action does not occur before the timer expires the SWT
generates an interrupt or hardware reset. The SWT can be configured to generate a reset or interrupt on an
initial time-out, a reset is always generated on a second consecutive time-out.
The SWT provides a window functionality. When this functionality is programmed, the servicing action
should take place within the defined window. When occurring outside the defined period, the SWT will
generate a reset.
27.3.2
Features
The SWT has the following features:
•
32-bit time-out register to set the time-out period
•
The unique SWT counter clock is the undivided low power internal oscillator (IRC 16 MHz), no
other clock source can be selected
•
Programmable selection of window mode or regular servicing
•
Programmable selection of reset or interrupt on an initial time-out
•
Master access protection
•
Hard and soft configuration lock bits
•
The SWT is started on exit of power-on phase (RGM phase 2) to monitor flash boot sequence
phase. It is then reset during RGM phase 3 and optionally enabled when platform reset is released
depending on value of flash user option bit 31 (WATCHDOG_EN).
27.3.3
Modes of operation
The SWT supports three device modes of operation: normal, debug and stop. When the SWT is enabled
in normal mode, its counter runs continuously. In debug mode, operation of the counter is controlled by
the FRZ bit in the SWT_CR. If the FRZ bit is set, the counter is stopped in debug mode, otherwise it
continues to run. In stop mode, operation of the counter is controlled by the STP bit in the SWT_CR. If