#include "stm32f4xx_iwdg.h"
#include "iwdg.h"

#define LSI_FREQUENCY 32000
#define COUNT_LENGTH 12
#define COUNT_MASK ((1 << COUNT_LENGTH)-1)


/** @brief IWDG Enable Watchdog Timer
 * The watchdog timer is started. 
 * The timeout period defaults to 512 milliseconds
 * unless it has been previously defined.
 */
void iwdg_start(void)
{
    IWDG_Enable();
}

/** @brief IWDG Set Period in Milliseconds
 *
 * The countdown period is converted into count and prescale values. The maximum
 * period is 32.76 seconds; values above this are truncated. Periods less than 1ms
 * are not supported by this library.
 *
 * A delay of up to 5 clock cycles of the LSI clock (about 156 microseconds)
 * can occasionally occur if the prescale or preload registers are currently busy
 * loading a previous value.
 * 
 * @param[in] period uint32_t Period in milliseconds (< 32760) from a watchdog
 * reset until a system reset is issued.
 */
void iwdg_set_period_ms(uint32_t period)
{
    uint32_t count, prescale, reload, exponent;

    /* Set the count to represent ticks of the 32kHz LSI clock */
    count = (period << 5);

    /* Strip off the first 12 bits to get the prescale value required */
    prescale = (count >> 12);
    if (prescale > 256) {
        exponent = IWDG_Prescaler_256; reload = COUNT_MASK;
    } else if (prescale > 128) {
        exponent = IWDG_Prescaler_256; reload = (count >> 8);
    } else if (prescale > 64) {
        exponent = IWDG_Prescaler_128; reload = (count >> 7);
    } else if (prescale > 32) {
        exponent = IWDG_Prescaler_64;  reload = (count >> 6);
    } else if (prescale > 16) {
        exponent = IWDG_Prescaler_32;  reload = (count >> 5);
    } else if (prescale > 8) {
        exponent = IWDG_Prescaler_16;  reload = (count >> 4);
    } else if (prescale > 4) {
        exponent = IWDG_Prescaler_8;   reload = (count >> 3);
    } else {
        exponent = IWDG_Prescaler_4;   reload = (count >> 2);
    }

    /* Avoid the undefined situation of a zero count */
    if (count == 0) {
        count = 1;
    }

    while (IWDG_GetFlagStatus(IWDG_FLAG_PVU) != RESET)
        ;
    IWDG_WriteAccessCmd(IWDG_WriteAccess_Enable);
    IWDG_SetPrescaler(exponent);
    while (IWDG_GetFlagStatus(IWDG_FLAG_RVU) != RESET)
        ;
    IWDG_SetReload(reload & COUNT_MASK);
}

/** @brief IWDG reset Watchdog Timer
 *
 * The watchdog timer is reset. The counter restarts from the value in the reload
 * register.
 */
void iwdg_reset(void)
{
    IWDG_ReloadCounter();
}