Target Application Performs Reset (Cortex-M) - Segger J-Link User Manual

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8.8

Target application performs reset (Cortex-M)

For Cortex-M based target CPUs if the target application contains some code that issues a
reset (e.g. a watchdog reset), some special care needs to be taken regarding breakpoints.
In general, a target reset will leave the debug logic of the CPU untouched meaning that
breakpoints etc. are left intact, however monitor mode gets disabled (bits in DEMCR get
cleared). J-Link automatically restores the monitor bits within a few microseconds, after
they have been detected as being cleared without explicitly being cleared by J-Link.
However, there is a small window in which it can happen that a breakpoint is hit before
J-Link has restored the monitor bits. If this happens, instead of entering debug mode, a
HardFault is triggered. To avoid hanging of the application, a special version of the Hard-
Fault_Handler is needed which detects if the reason for the HardFault was a breakpoint
and if so, just ignores it and resumes execution of the target application. A sample for
such a HardFault handler can be downloaded from the SEGGER website: https://www.seg-
ger.com/downloads/appnotes "Generic SEGGER HardFault handler".
J-Link / J-Trace (UM08001)
CHAPTER 8 Target application performs reset (Cortex-M)
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