APIC Timer: Difference between revisions
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Added information for recommended (stated by Intel's manual) method of determining APIC timer frequency |
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== Initializing == |
== Initializing == |
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''Please note that this is the recommended way of determining the frequency of the APIC timer.'' |
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'''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. |
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There are several ways to do this, but all of them use a different, CPU bus frequency independent clock source to do that. Examples: [[RTC|Real Time Clock]], [[TSC|TimeStamp Counter]], PIT or even polling [[CMOS#Getting_Current_Date_and_Time_from_RTC|CMOS registers]]. In this tutorial we will use the good old PIT, as it's the easiest. Steps that need to be done: |
There are several ways to do this, but all of them use a different, CPU bus frequency independent clock source to do that. Examples: [[RTC|Real Time Clock]], [[TSC|TimeStamp Counter]], PIT or even polling [[CMOS#Getting_Current_Date_and_Time_from_RTC|CMOS registers]]. In this tutorial we will use the good old PIT, as it's the easiest. Steps that need to be done: |
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* Reset APIC to a well known state |
* Reset APIC to a well known state |
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