There will be in general built in self tests for the micro controller, for example memory (RAM, Flash) self test etc. How much important are these tests, I mean to should i always be checking them on every power cycle? The other thing is suppose i installed the system for production and one of the tests failed and the micro controller does not run, then how do i know it is because of memory failure? since controller completely failed and i cannot execute any my code i cannot turn LED etc. Is there any mechanism by which i can still know this?

 

Is there something like a Class B Safety requirement for the controller application? If yes, then power on self checks are mandatory.

https://www.embeddedrelated.com/showarticle/840.php
https://www.microchip.com/design-centers/home-appliance/class-b-safety-software

The LED(s) can have a Diagnostic LED timing signals (speed, duration, on/off duty-cycle modes) indicating pass/failure during execution of self-checks beyond a simple on/off indication of total failure.

 

I recall doing POST (Power On Self Test) and diagnostics on Data General Nova computers.
The diagnostic code tested every possible operation and machine code of the CPU.
The memory tests ran very comprehensive moving bit patterns on core memory.

IBM PC BIOS firmware runs POST every time the power is turned on.
I am certain BIOS still performs some kind of POST.

You can create your own POST for any MCU you plan to use.

 

Modern micros have some HW facilities that help handling software fault issues -

Watchdog timer - https://www.embedded.com/electronics-blogs/beginner-s-corner/4023849/Introduction-to-Watchdog-Timers

Address Traps - https://en.wikipedia.org/wiki/Trap_(computing)


Regards, Dana.

 

On my boards, I usually include a test point that attaches to a free port pin with with a passive 100K pull-up.

If the board is powered-on while the pin is asserted low, it forces the execution of test code on the chip.

Depending on the application, the test code may exercise various hardware on both the chip and the board. This is usually in conjunction with a custom test fixture that supplies signals to help exercise and diagnose problems on the board.

In addition, I include power-up test code that runs sanity tests on the hardware each power-on.

Finally: I don't use watchdog timers for production firmware. These are for lazy programmers who won't test 100% of their code prior to manufacturing, IMHO.