APIC Timer: Difference between revisions

'''NOTE:''' According to Intel's documentation for IA-32 (x86) and Intel 64 (x86_64), APIC timer's frequency is equal to the bus' frequency '''OR''' the core crystal's frequency divided by the chosen frequency divider. The bus' and the core crystal's frequency can be found in the [[CPUID|CPUID]] functions [https://sandpile.org/x86/cpuid.htm#level_0000_0015h 0x15] and [https://sandpile.org/x86/cpuid.htm#level_0000_0016h 0x16], respectively. Through CPUID.0x15 can also be determined the TSC frequency. The frequency of the APIC timer depends on whether the system is using local APIC or ''discrete'' APIC ([https://en.wikipedia.org/wiki/Advanced_Programmable_Interrupt_Controller 82489DX]). When the local APIC is built in core's crystal, the APIC timer is using core's frequency. Otherwise, it is using the bus frequency.