Why does a "KRNL ERROR" or a "SWTO Error" occur?

FAQ #101069

 

Symptom
In some very special circumstances (if a PCD is stressed by extreme external influences) the PCD3 automatically executes a reboot and then goes in HALT (if the software watchdog is programmed, the PCD automatically goes in RUN after the restart).
When going online and reading the PCD history, an entry "KERNEL ERROR" (on firmware versions 1.08.xx and earlier) or "SWTO ERROR" (on firmware versions 1.10.xx and later) can be found.

Reason
For saftey reasons the PCD executes a reboot in case the System Watchdog is no longer called within a specific time (this is the same behavior as the Software Watchdog, but directly on firmware level). In case of the Kernel Error a task-overload has been detected (FW indicating a Kernel Error (1.08.xx and earlier) do not feature the System Watchdog). 
Such a situation could e.g. be caused by an Ethernet telegram bombardement of several thousend telegrams per second or if a connected FDL network is disturbed heavily over a long time. In such a situation the PCD (with FW older than 1.10.xx) does only treat the interrupts generated by e.g. the IP telegrams and no longer executes the rest of its tasks (for security reasons, this state is interrupted by the automated reboot of the system).
 
Solution
A new Kernel together with other improvements which can avoid situations leading to SWTO Errors have been implemented in firmware version 1.10.xx (or in the special firmware with new kernel 1.08.19.12). Thanks to these improvements the PCD is even more robust against the mentioned influences which can cause a "SWTO Error" (or a "KERNEL ERROR").

Important

• Please note that in case a Software Watchdog is programmed, the PCD does automatically go in RUN after the restart executed by the System Watchdog (if no Software Watchdog is programmed, the PCD goes in HALT after the reboot caused by the System Watchdog)
• In general it is recommended using firmware version 1.10.16 or later rather than 1.08.19.12.