SysTick Public APIs

Functions
ERR_te	systick_init (SYSTICK_CFG_ts const *systick_cfg)
	Initializes and starts the SysTick timer.
void	systick_deinit (void)
	Deinitializes the SysTick timer.
void	systick_get_def_cfg (SYSTICK_CFG_ts *systick_cfg_o)
	Populates a configuration structure with the default SysTick settings.
uint32_t	systick_get_ms (void)
	Returns the number of milliseconds elapsed since SysTick was initialized.
void	SysTick_Handler (void)
	SysTick exception handler. Increments the millisecond counter on each 1 ms wrap.

Detailed Description

Function Documentation

systick_init()

ERR_te systick_init

(

SYSTICK_CFG_ts const *

systick_cfg

)

Initializes and starts the SysTick timer.

See also

systick_init

Definition at line 41 of file arm_cortex_m4_systick.c.

                                                       {
    if(internal_state.initialized) {
        return ERR_MODULE_ALREADY_INITIALIZED;
    }
 
    // Disable SysTick before reconfiguring
    SYSTICK->SYST_CSR &= ~(1U << SYST_CSR_ENABLE);
 
    // Clear internal state
    internal_state = (struct internal_state_s){ 0 };
 
    // Configure interrupt enable
    SYSTICK->SYST_CSR &= ~(1U << SYST_CSR_TICKINT);
    SYSTICK->SYST_CSR |= (systick_cfg->interrupt << SYST_CSR_TICKINT);
 
    // Configure clock source
    SYSTICK->SYST_CSR &= ~(1U << SYST_CSR_CLKSOURCE);
    SYSTICK->SYST_CSR |= (systick_cfg->clk_source << SYST_CSR_CLKSOURCE);
 
    // Clear current value
    SYSTICK->SYST_CVR = 0;
 
    // Compute reload value for a 1 ms tick period from the AHB clock
    uint32_t cpu_clk = rcc_get_ahb_clk();
    uint32_t one_ms_clk_cycle = cpu_clk / 1000;
    uint32_t reload_value = one_ms_clk_cycle + 1;
    if (reload_value == 0 || reload_value > 0x01000000U) {
        return ERR_UNKNOWN;
    }
 
    // Set reload value (24-bit register)
    SYSTICK->SYST_RVR &= ~(0xFFFFFF);
    SYSTICK->SYST_RVR |= (reload_value - 1);
 
    // Enable SysTick
    SYSTICK->SYST_CSR |= (1U << SYST_CSR_ENABLE);
 
    internal_state.initialized = true;
 
    return ERR_OK;
}

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systick_deinit()

void systick_deinit

(

void

)

Deinitializes the SysTick timer.

See also

systick_deinit

Definition at line 84 of file arm_cortex_m4_systick.c.

                          {
    if(!internal_state.initialized) {
        return;
    }
 
    SYSTICK->SYST_CSR &= ~(1U << SYST_CSR_ENABLE);
 
    internal_state = (struct internal_state_s){ 0 };
 
    SYSTICK->SYST_CSR &= ~(1U << SYST_CSR_TICKINT);
    SYSTICK->SYST_CSR &= ~(1U << SYST_CSR_CLKSOURCE);
 
    SYSTICK->SYST_CVR = 0;
 
    SYSTICK->SYST_RVR &= ~(0xFFFFFF);
}

systick_get_def_cfg()

void systick_get_def_cfg

(

SYSTICK_CFG_ts *

systick_cfg_o

)

Populates a configuration structure with the default SysTick settings.

See also

systick_get_def_cfg

Definition at line 102 of file arm_cortex_m4_systick.c.

                                                        {
    systick_cfg_o->clk_source = SYSTICK_CLK_SOURCE_PROCESSOR;
    systick_cfg_o->interrupt = SYSTICK_IT_TRUE;
}

systick_get_ms()

uint32_t systick_get_ms

(

void

)

Returns the number of milliseconds elapsed since SysTick was initialized.

See also

systick_get_ms

Definition at line 108 of file arm_cortex_m4_systick.c.

                              {
    if(!internal_state.initialized) {
        return 0;
    }
 
    return internal_state.elapsed_ms;
}

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SysTick_Handler()

void SysTick_Handler

(

void

)

SysTick exception handler. Increments the millisecond counter on each 1 ms wrap.

Called automatically by the Cortex-M4 exception mechanism every time the SysTick counter reaches zero. Must not be called directly from application code.

Definition at line 123 of file arm_cortex_m4_systick.c.

                           {
    internal_state.elapsed_ms++;
}