What is the Generic Timer?

The Generic Timer provides a standardized timer framework for Arm cores. The Generic Timer includes a System Counter and set of per-core timers, as shown in the following diagram:

System counter block diagram

The System Counter is an always-on device, which provides a fixed frequency incrementing system count. The system count value is broadcast to all the cores in the system, giving the cores a common view of the passage of time. The system count value is between 56 bits and 64 bits in width, with a frequency typically in the range of 1MHz to 50MHz.

Note: The Generic Timer only measures the passage of time. It does not report the time or date. Usually, an SoC would also contain a Real-Time Clock (RTC) for time and date.

Each core has a set of timers. These timers are comparators, which compare against the broadcast system count that is provided by the System Counter. Software can configure timers to generate interrupts or events in set points in the future. Software can also use the system count to add timestamps, because the system count gives a common reference point for all cores.

In this guide, we will explain the operation and configuration of both the timers and the System Counter.

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