Watchdog Autosar Stack

What is watchdog timer?

• It is an electronic timer that used to detect and recover from computer malfunctions or any issue happens in software.

How it works?

• During normal Operation, The computer regularly resets the watchdog timer to prevent it from timing out.

What if any issue happened in software due to a hardware fault or a program error?

• The computer fails to reset the watchdog, the timer will generate a timeout signal.
• The timeout signal is used to initiate corrective actions.

Watchdog Stack Architecture:

• The need to monitor the running SW and to take one or more recovery action in case of detected failure.
• WdgM is responsible for that which located in the AUTOSAR service layer.
• WdgM need to communicate to either an internal or external watchdog .
• And if many WDG devices are used to enable the WdgM to select between them through Wdgif.
• WDG initialize or edit wdg hardware registers, and to refresh the wdg.
• We need to communicate with external wdg device through Dio pin or SPI.

AUROSAR Watchdog concepts:

Supervision function: Defines the way that WdgM monitors the SW.

Supervision types:

1/ Alive Supervision for periodicity monitoring (SW aliveness)

• Kind of supervision that checks if a supervised entity executed sufficiently often and not too often (including tolerances).
• Timing focus (Check SW time rate) based on configurations.

2/ Deadline Supervision for execution time monitoring

• Kind of supervision that checks if the execution time between to checkpoints are lower than a given upper execution time limit.
• Timing focus.

3/ Logical Supervision (Internal and external): Program flow monitoring

• Kind of supervision that checks if the software is executer in the sequence defined by the programmer.
• Logical Sequence Focus.

Supervised Entity: is the unit of supervision for the WdgM:

Examples of a SE:

1. Feature.
2. Function in a BSW Module or SW-Check.
3. Entire BSW Module.
4. Entire SW-C.

• There maybe zero, one or more supervised entities in a software component(SW-C) or BSW module.
• Each supervised entity can be supervised by a different supervision function or a combination of them.

Checkpoint: is a point in the control flow of a SE where the activity is reported to the WdgM.

A supervised entity is defined by 1 or more checkpoints.

Watchdog mode:

In the context of the watchdog manger a mode is defined by:

1/ Set of supervised entities (SEs).

2/ Set of Alive supervisions.

3/ Set of Deadline supervisions.

4/ Set of Logical Supervisions.

Supervision Cycle: is the period at which Wdgm_MainFunction is called.