µTasker Forum > NXPTM M522XX, KINETIS and i.MX RT

reinstalling serial loader with fallback loader, how to start fallback loader?


I am reading the test drive document for the Serial Loader: https://www.utasker.com/docs/iMX/uTaskerLoader_TestDrive.pdf

the doc mentions:
"recovery via serial “Fall-back” loader when a faulty application or a faulty serial loader is installed"

But the doc doesn't describe how this actually happens.   How does uTaskerBoot know to start the fallback loader instead of the serial loader if the serial loader is corrupted?

I see the fallback loader start if the serial loader is missing completely, but how would this work if the serial loader is present, but corrupted or needs to be updated?



The fall-back loader is intended mainly as a loader to install new serial loader versions. It can be started from the application using the "fboot" command or from the serial loader using the "fb" command.
If the serial loader were corrupted (check-sum or authentication is invalid) it will behave as if it is not available and start the fall-back loader so that an un-corrupted version can be loaded.
Typically the primary loader is configured to start the fall-back loader if it has counted 16 watchdog resets:
- that means that there is a serial loader (or more likely) an application that is failing (possibly not allowing the serial loader to be commanded)
- after the failure has taken place 16x (if an application had been loaded that almost immediately hard faults due to a certain error were loaded it would watchdog reset every few seconds) the boot loader will start so that the user has the opportunity to load a new serial loader version
- the fall-back loader will typically automatically start the serial loader after 15s, thus giving the user the opportunity to load a new application
- the serial loader typically times out after 60s (when no activity is taking place) and so the cycle will repeat - the idea is that the user should not need to wait that long before the fall-back and then the serial loaders are automatically offered in such a case




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