arm_timer.c File Reference

Implementation of the ARM generic system timer driver (CNTP). More...

#include "arm_timer.h"
#include "asm/asm_helper.h"
#include "fdt/fdt.h"
#include "utils/kprintf.h"
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>

Include dependency graph for arm_timer.c:

Data Structures
union	cntp_ctl_el0_t
	CNTP_CTL_EL0 (EL1 Physical Timer Control Register) layout. More...

Macros
#define	MAX_TIMER_INTERRUPTS   4
	Maximum number of "interrupts" entries the timer node may have.
#define	NS_PHYSICAL_TIMER_INTR_INDEX   1
	Index of the non-secure EL1 physical timer in the ARM generic timer's standard 4-entry "interrupts" property (secure, non-secure, virtual, hypervisor). This is the PPI fired by CNTP_*.
#define	MILLISECONDS_PER_SECOND   1000U
	Number of milliseconds in a second, used to derive CNTP_TVAL_EL0 ticks from a millisecond period and CNTFRQ_EL0.

Typedefs
typedef union cntp_ctl_el0_t	cntp_ctl_el0_t
	CNTP_CTL_EL0 (EL1 Physical Timer Control Register) layout.

Functions
static void	timer_isr (void *priv)
	ISR for the EL1 physical timer interrupt.
static bool	set_period (uint64_t period_ms)
	Compute and store the CNTP_TVAL_EL0 tick count for a tick period.
static bool	setup_isr (uint32_t int_id, handler_data_t handler)
	Register the tick handler and enable the EL1 physical timer.
bool	setup_arm64_sys_timer (const void *fdt, int node_offset, uint64_t milliseconds, handler_data_t handler)
	Configure the system timer's tick period and interrupt handler.

Variables
static uint64_t	period_ticks
	Number of ticks CNTP_TVAL_EL0 must be loaded with to fire once per configured tick period; set by set_period() and consumed by timer_isr() to re-arm the timer after each interrupt.
static handler_data_t	tick_handler
	Handler registered by the caller of setup_arm64_sys_timer(), invoked from timer_isr() on every tick.

Detailed Description

Implementation of the ARM generic system timer driver (CNTP).

Author

Abhin Parekadan Jose

Date

2026-06-28

Function Documentation

set_period()

static bool set_period ( uint64_t  period_ms )

static

Compute and store the CNTP_TVAL_EL0 tick count for a tick period.

Parameters

period_ms

Desired tick period in milliseconds.

Returns

true if the period fits in CNTP_TVAL_EL0, false otherwise.

setup_arm64_sys_timer()

bool setup_arm64_sys_timer	(	const void *	fdt,
		int	node_offset,
		uint64_t	milliseconds,
		handler_data_t	handler
	)

Configure the system timer's tick period and interrupt handler.

Parameters

fdt	Pointer to the Flattened Device Tree (FDT) blob, which may be used to discover timer properties and configuration.
node_offset	Offset of the timer node in the FDT.
milliseconds	Desired tick period in milliseconds.
handler	Handler function and private data to invoke when the timer interrupt fires.

Returns

true if the timer was configured successfully, false otherwise.

setup_isr()

static bool setup_isr ( uint32_t  int_id, handler_data_t  handler  )

static

Register the tick handler and enable the EL1 physical timer.

Parameters

int_id	GIC INTID of the EL1 physical timer interrupt.
handler	Handler function and private data to invoke on each tick.

Returns

true if the ISR was registered and the timer enabled successfully, false otherwise.

timer_isr()

static void timer_isr ( void *  priv )

static

ISR for the EL1 physical timer interrupt.

Masks the timer, invokes the registered tick handler if the timer condition was actually met, reloads CNTP_TVAL_EL0 for the next period, and unmasks/re-enables the timer.

Parameters

priv	Unused; registered with NULL private data via icu_register_irq().