Method and computer system to execute safe code

A method to execute safe code in an embedded computer system including hardware and software, the hardware including at least one processor with at least one processor core, and at least one memory, the at least one processor core configured to implement at least three execution levels and to implement a mechanism to switch between at least two modes, including an unsafe mode and a safe mode, the at least one memory partitioned in a safe memory and an unsafe memory, the hardware configured such that data stored in the safe memory is accessible via the software only if the at least one processor core is in the safe mode, the software including an unsafe operating system configured to execute at a first execution level, at least a first program configured to execute at a second execution level, and a second program for changing a mode of the at least one processor core from the unsafe mode to the safe mode and from the safe mode to the unsafe mode, the second program configured to execute on a third execution level, the at least one first program including a safe code and an unsafe code, the method comprising:

• executing the at least one first program as a process of the unsafe operating system;
• triggering, via the at least one first program, a change from the unsafe mode to the safe mode via executing a first command and a change from the safe mode to the unsafe Mode via executing a second command;
• reacting, via the at least on processor core, to the execution of the first command and the second command by switching an execution level from the second execution level to the third execution level and by starting execution of the second program to change the mode of the at least one processor core;
• and
• reacting, via the at least one processor core, to all execution attempts of the unsafe operating system by switching the execution level from the second execution level to the third execution level and by starting execution of a program to change the mode of the at least one processor core.