Counter Timer

Timer

https://developer.arm.com/documentation/102379/0101/The-processor-timers?lang=en

Count & Freq §

• CNTPCT_EL0
  • Current System Count Value
• CNTFRQ_EL0
  • Frequency of the System Count
  • Write-able at the highest implemented EL, Readable at all EL

Registers §

Register	Purpose
<timer>_CTL_EL<x>	Control register
<timer>_CVAL_EL<x>	Comparator value
<timer>_TVAL_EL<x>	Timer value

Timer	Register prefix	EL
EL1 physical timer	CNTP	EL0
EL1 virtual time	CNTV	EL0
Non-secure EL2 physical timer	CNTHP	EL2
Non-secure EL2 virtual timer	CNTHV	EL2
EL3 physical timer	CNTPS	EL1
Secure EL2 physical timer	CNTHPS	EL2
Secure EL2 virtual timer	CNTHVS	EL2

Configuration §

CVAL §

• Comparator Register
• 64bit Timer Condition Met: CVAL <= System Count

TVAL §

• Timer Register
• 32bit Timer Condition Met: TVAL <= 0

정리 §

• CVAL은 System Count와 일치할 때..
• TVAL은 TVAL 만큼 Count한 이후에..

Interrupts §

CNTP_CTL §

• ENABLE: Enables the timer
• IMASK: Interrupt Mask
• ISTATUS: Reports whether the timer is firing (=CVAL <= System Count) when ENABLE==1

Link to original

https://cirosantilli.com/linux-kernel-module-cheat/arm-timer.html

Virtual Memory §

• ARMv8 Programmers Guide: Chapter 12: The Memory Management Unit
• Chapter 12 The Memory Management Unit