drv_hwtimer.c 中出现一个参数被转成不同的类型?

static void timer_init(struct rt_hwtimer_device *timer, rt_uint32_t state)

tim_device = (struct stm32_hwtimer *)timer;

typedef struct rt_hwtimer_device
{
    struct rt_device parent;
    const struct rt_hwtimer_ops *ops;
    const struct rt_hwtimer_info *info;
    rt_int32_t freq;                /* counting frequency set by the user */
    rt_int32_t overflow;            /* timer overflows */
    float period_sec;
    rt_int32_t cycles;              /* how many times will generate a timeout event after overflow */
    rt_int32_t reload;              /* reload cycles(using in period mode) */
    rt_hwtimer_mode_t mode;         /* timing mode(oneshot/period) */
} rt_hwtimer_t;

struct stm32_hwtimer
{
    rt_hwtimer_t time_device;
    TIM_HandleTypeDef    tim_handle;
    IRQn_Type tim_irqn;
    char *name;
};