System Timer Ticks – Definitions
To understand the concept of the system timer – and how it can be synchronized to external sources – we need to look into the underlying hardware.
System timer ticks are generated and managed by a logical unit that we call the System Timer. The duration or period of a system tick can be programmed and synchronized to external timer sources. The system timer is driven by dedicated timer hardware (normally one found in the local APIC) that is connected to a clock signal of determined frequency/duration. Frequency/duration are specific for the actual hardware platform running INtime – and INtime does map the logical unit “System Timer” consistently to any actual hardware platform.
This timer hardware counts the clock cycles and generates an interrupt when the number of cycles matches the value loaded into the hardware's reload register. Every interrupt generated by the timer hardware is one system timer tick.
The interrupt for the actual system timer tick loads the hardware timer’s reload register again and the time towards the next system tick starts.