The STM32WB offers a Cortex M4 as main CPU and also an M0 as a secondary CPU for real-time tasks such as networking. That's an example of what you're looking for.
The user requests an application to run by making a system call to get it started
In a case where electrical current leakage from the circuit occurs, the GFCI would do the following: 1. Sense the current leakage. 2. Trip the circuit. 3. Cut off the electricity. Electrical current leakage needs to be sensed at once. Without it being detected, it cant be dealt with. The second step consists of tripping the circuit so at to remove the flow of electricity. The third step is to Cut the electricity off so to stop the leakage and be safe.
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During the boot process. You hold down a certain key (usually F2 or F8 (Function keys)), the beginning of the boot process checks for the keypress, and if it's detected, launches the utility.