arm_cortex_m4_systick.c

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#include "arm_cortex_m4_systick.h"
#include "arm_cortex_m4.h"
#include "err.h"
#include "stm32f401re_rcc.h"

struct internal_state_s {
    uint32_t volatile elapsed_ms;

    bool initialized;
};

static struct internal_state_s internal_state;


ERR_te systick_init(SYSTICK_CFG_ts const *systick_cfg) {
    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;
}

void systick_deinit(void) {
    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);
}

void systick_get_def_cfg(SYSTICK_CFG_ts *systick_cfg_o) {
    systick_cfg_o->clk_source = SYSTICK_CLK_SOURCE_PROCESSOR;
    systick_cfg_o->interrupt = SYSTICK_IT_TRUE;
}

uint32_t systick_get_ms(void) {
    if(!internal_state.initialized) {
        return 0;
    }
 
    return internal_state.elapsed_ms;
}

void SysTick_Handler(void) {
    internal_state.elapsed_ms++;
}