Debug In Low Power Modes - NXP Semiconductors MKL27Z128VFM4 Reference Manual

Functional description
An asserted RESET pin will cause an exit from any VLLS mode, returning the device to
normal RUN mode. When exiting VLLS via the RESET pin, RCM_SRS[PIN] and
RCM_SRS[WAKEUP] are set.

14.5.6 Debug in low power modes

When the MCU is secure, the device disables/limits debugger operation. When the MCU
is unsecure, the ARM debugger can assert two power-up request signals:
• System power up, via SYSPWR in the Debug Port Control/Stat register
• Debug power up, via CDBGPWRUPREQ in the Debug Port Control/Stat register
When asserted while in RUN, WAIT, VLPR, or VLPW, the mode controller drives a
corresponding acknowledge for each signal, that is, both CDBGPWRUPACK and
CSYSPWRUPACK. When both requests are asserted, the mode controller handles
attempts to enter STOP and VLPS by entering an emulated stop state. In this emulated
stop state:
• the regulator is in run regulation,
• the MCG-generated clock source is enabled,
• all system clocks, except the core clock, are disabled,
• the debug module has access to core registers, and
• access to the on-chip peripherals is blocked.
No debug is available while the MCU is in LLS or VLLS modes. LLS is a state-retention
mode and all debug operation can continue after waking from LLS, even in cases where
system wakeup is due to a system reset event.
Entering into a VLLS mode causes all of the debug controls and settings to be powered
off. To give time to the debugger to sync with the MCU, the MDM AP Control Register
includes a Very-Low-Leakage Debug Request (VLLDBGREQ) bit that is set to configure
the Reset Controller logic to hold the system in reset after the next recovery from a VLLS
mode. This bit allows the debugger time to reinitialize the debug module before the
debug session continues.
The MDM AP Control Register also includes a Very Low Leakage Debug Acknowledge
(VLLDBGACK) bit that is set to release the ARM core being held in reset following a
VLLS recovery. The debugger reinitializes all debug IP, and then asserts the
VLLDBGACK control bit to allow the RCM to release the ARM core from reset and
allow CPU operation to begin.
The VLLDBGACK bit is cleared by the debugger (or can be left set as is) or clears
automatically due to the reset generated as part of the next VLLS recovery.
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KL27 Sub-Family Reference Manual , Rev. 5, 01/2016
Freescale Semiconductor, Inc.