5.5.6 VE - differences in timing

Fixed Virtual Platforms (FVPs) allow software to run in a functionally accurate simulation. However, because of the balance of fast simulation speed and timing accuracy, in some situations the models might behave unexpectedly.

When code interacts with real world devices like timers and keyboards, data arrives in the modeled device in real-world, or wall-clock, time. However, simulation time can be running much faster than the wall clock. This difference means that a single keypress might be interpreted as several repeated key presses, or a single mouse click incorrectly becomes a double click.

The VE FVPs provide the Rate Limit feature to match simulation time to wall-clock time. Enabling the rate limit prevents the model from running faster than wall-clock time. Enable it with either the Rate Limit button in the CLCD display, or the rate_limit-enable model instantiation parameter. This precaution avoids issues with two clocks running at different rates. For interactive applications, ARM recommends enabling the rate limit.

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