Implements the SysTick utility functions. More...

#include "systick.h"

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Functions
void	systick_init (void)
	Initializes the SysTick timer module.
void	systick_reset (void)
	Resets the SysTick timer value.
void	systick_tick (void)
	Increments the SysTick timer tick counter.
unsigned int	systick_current (void)
	Returns the current SysTick tick counter value.
void	systick_timer_set (SYSTICK_Timer *timer, unsigned int delay_ticks)
	Sets and starts a SysTick software timer.
SYSTICK_Timer_Status	systick_timer_elapsed (SYSTICK_Timer *timer)
	Checks whether a SysTick software timer has expired.
unsigned int	systick_timer_remaining (SYSTICK_Timer *timer)
	Returns the remaining time before a SysTick timer expires.
void	systick_timer_wait (unsigned int ticks)
	Blocks execution for a specified number of SysTick ticks.
void	systick_timer_cancel (SYSTICK_Timer *timer)
	Cancels a running SysTick software timer.

Variables
volatile unsigned int	systick_tick_value

Detailed Description

Implements the SysTick utility functions.

This file provides the implementation of the SysTick utility functions declared in systick.h. It manages a software timer based on the SysTick peripheral, allowing for non-blocking delays and periodic tasks.

Author: g.raf

Date: 2026-01-24

Version: 1.0 Release

Copyright: Copyright (c) 2026 g.raf Released under the GPLv3 License. (see LICENSE in repository)

Note: This file is part of a larger project and subject to the license specified in the repository. For updates and the complete revision history, see the GitHub repository.

See also: https://github.com/0x007e/utils-systick "Systick GitHub Repository"

Function Documentation

◆ systick_current()

unsigned int systick_current ( void )

Returns the current SysTick tick counter value.

This function reads the current value of the internal SysTick tick counter (systick_tick_value) in an atomic operation to prevent race conditions during concurrent access from interrupts. The returned value represents the elapsed system ticks since the last reset or initialization of the SysTick module.

Returns: The current SysTick tick counter value.

Note: The access is performed inside an ATOMIC_BLOCK to ensure data consistency when interrupts may update the tick value.

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◆ systick_init()

void systick_init ( void )

Initializes the SysTick timer module.

This function initializes the SysTick timer by resetting its internal state and preparing it for subsequent use. It calls systick_reset() to ensure the timer starts from a known default state.

Typically, this function should be called once during system initialization before any SysTick-based timing operations are performed.

Note: This function does not start the timer automatically; it only resets
and initializes the SysTick module.

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◆ systick_reset()

void systick_reset ( void )

Resets the SysTick timer value.

This function clears the internal SysTick tick counter by setting systick_tick_value to zero. It ensures that the timer restarts counting from the beginning, which is useful during initialization or when restarting time measurements.

Note: This function does not alter the SysTick configuration or status. It only resets the tick counter value.

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◆ systick_tick()

void systick_tick ( void )

Increments the SysTick timer tick counter.

This function increases the internal systick_tick_value by one. It should be called periodically—typically from the SysTick interrupt service routine—to maintain an accurate system tick counter used for software timing and scheduling operations.

Note: This function must be invoked at a constant rate to ensure correct timekeeping for all SysTick-based timers.

◆ systick_timer_cancel()

void systick_timer_cancel ( SYSTICK_Timer * timer )

Cancels a running SysTick software timer.

This function stops a SysTick timer by setting its status to SYSTICK_Timer_Expired, effectively marking it as completed regardless of its current tick count. Once canceled, the timer will be considered expired and will no longer count down or trigger expiration checks.

Parameters

[in,out] timer Pointer to the SysTick timer instance to cancel.

Note: This function does not modify the timer’s expiration value; it only updates the status flag to indicate expiration.

◆ systick_timer_elapsed()

SYSTICK_Timer_Status systick_timer_elapsed ( SYSTICK_Timer * timer )

Checks whether a SysTick software timer has expired.

This function determines if the specified SYSTICK_Timer instance has reached its expiration tick value. If the current SysTick count has passed the timer's expire value, the timer status is updated to SYSTICK_Timer_Expired. Otherwise, the timer remains in the running state.

Parameters

[in,out] timer Pointer to the SysTick timer instance to check.

Returns

The current status of the timer:

Note: The comparison uses signed arithmetic to handle counter wraparound
conditions correctly when the SysTick tick counter overflows.

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◆ systick_timer_remaining()

unsigned int systick_timer_remaining ( SYSTICK_Timer * timer )

Returns the remaining time before a SysTick timer expires.

This function calculates the number of SysTick ticks remaining until the specified SYSTICK_Timer instance reaches its expiration value. If the timer has already expired, its status is updated to SYSTICK_Timer_Expired, and the function returns zero.

Parameters

[in,out] timer Pointer to the SysTick timer instance to query.

Returns: The number of SysTick ticks remaining until expiration, or 0 if the timer has already expired.

Note: The comparison uses signed arithmetic to correctly handle counter wraparound when the SysTick tick counter overflows.

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◆ systick_timer_set()

void systick_timer_set	(	SYSTICK_Timer *	timer,
		unsigned int	delay_ticks )

Sets and starts a SysTick software timer.

This function initializes a given SYSTICK_Timer instance by setting its expiration tick value relative to the current SysTick count. The timer is configured to expire after the specified number of delay_ticks and marked as running.

Parameters

[in,out]	timer	Pointer to the SysTick timer instance to configure.
[in]	delay_ticks	Number of SysTick ticks after which the timer should expire.

Note: The timer must be periodically checked (e.g., via systick_timer_expired()) to determine when it has reached its expiration.

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◆ systick_timer_wait()

void systick_timer_wait ( unsigned int ticks )

Blocks execution for a specified number of SysTick ticks.

This function creates a temporary SYSTICK_Timer instance and waits until it expires. The function blocks program execution by polling the timer status in a busy-wait loop, using a NOP instruction for each iteration to prevent compiler optimization and reduce power consumption on some architectures.

Parameters

[in] ticks The number of SysTick ticks to wait before returning.

Note: This is a blocking delay function and should only be used when precise timing is required, and multitasking is not critical. For non-blocking timing, use SYSTICK_Timer with periodic checks via systick_timer_elapsed() instead.

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Variable Documentation

◆ systick_tick_value

volatile unsigned int systick_tick_value

Functions

Variables

Detailed Description

Function Documentation

◆ systick_current()

◆ systick_init()

◆ systick_reset()

◆ systick_tick()

◆ systick_timer_cancel()

◆ systick_timer_elapsed()

◆ systick_timer_remaining()

◆ systick_timer_set()

◆ systick_timer_wait()

Variable Documentation

◆ systick_tick_value