Doug Spencer writes:

For one thing, to pass certification at level-D, your model has to be
deterministically "hard" real-time to process inputs and outputs in a
particular set time. This doesn't mean merely having a fast CPU and
memory, this means that an interrupt to the system is handled within a
known and specified time period with no overage.

Without a hard real-time response, the flight model cannot be
accurately portrayed at all times.

Not every application requires a certification of this kind.

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