rtt的io设备框架面向对象学习-硬件定时器设备

news2024/12/21 20:24:57

1.硬件定时器设备类对象图全貌

请添加图片描述
设备驱动层的硬件定时器类是实现类，是需要各个BSP实现的。其继承自设备驱动框架层的硬件定时器设备基类。一般设备驱动框架层及以上的类都是rtt官方写好的抽象类。

上图采用c++的纯虚函数来表示需要子类实现的父类方法——或者说是父类对子类的约束，当然在rtt的oopc中是通过函数指针实现的。

可以看到设备驱动层是stm32硬件定时器或者别的芯片厂家的硬件定时器类的所在。
rtt的oopc中每类都有对应的构造函数（初始化函数）。

以对象图中stm32硬件定时器设备类为起点分析其类定义和构造函数。

2.stm32硬件定时器设备类及其构造函数

如第1节对象图，在/ bsp / stm32 / libraries / HAL_Drivers / drivers /drv_tim.c中定义了stm32硬件定时器设备类及其构造函数，如下

类定义：

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

类实例化

static struct stm32_hwtimer stm32_hwtimer_obj[] =

其构造函数

static int stm32_hwtimer_init(void)
{
    int i = 0;
    int result = RT_EOK;

    for (i = 0; i < sizeof(stm32_hwtimer_obj) / sizeof(stm32_hwtimer_obj[0]); i++)
    {
        stm32_hwtimer_obj[i].time_device.info = &_info;
        stm32_hwtimer_obj[i].time_device.ops  = &_ops;//重写父类方法
        if (rt_device_hwtimer_register(&stm32_hwtimer_obj[i].time_device,
            stm32_hwtimer_obj[i].name, &stm32_hwtimer_obj[i].tim_handle) == RT_EOK)
        {
            LOG_D("%s register success", stm32_hwtimer_obj[i].name);
        }
        else
        {
            LOG_E("%s register failed", stm32_hwtimer_obj[i].name);
            result = -RT_ERROR;
        }
    }

    return result;
}
INIT_BOARD_EXPORT(stm32_hwtimer_init);

可以看到，stm32_hwtimer_init是stm32硬件定时器设备类的构造函数，它所干的事，主要是重写父类的方法，如下定义

static const struct rt_hwtimer_ops _ops =
{
    .init = timer_init,
    .start = timer_start,
    .stop = timer_stop,
    .count_get = timer_counter_get,
    .control = timer_ctrl,
};

然后调用其父类——硬件定时器设备基类——的构造函数rt_device_hwtimer_register完成接下来的构造流程。

3 硬件定时器设备基类及其构造函数

在/ components / drivers / include / drivers /hwtimer.h中定义了硬件定时器设备基类：

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;

其中需要子类实现的方法定义如下

struct rt_hwtimer_ops
{   
     void (*init)(struct rt_hwtimer_device *timer, rt_uint32_t state);    
     rt_err_t (*start)(struct rt_hwtimer_device *timer, rt_uint32_t cnt, rt_hwtimer_mode_t mode);    
     void (*stop)(struct rt_hwtimer_device *timer);    
     rt_uint32_t (*count_get)(struct rt_hwtimer_device *timer);    
     rt_err_t (*control)(struct rt_hwtimer_device *timer, rt_uint32_t cmd, void *args);
 };

可以看到第一个形参是本类的指针——这就模拟了面向对象的this指针。

在/ components / drivers /hwtimer/hwtimer.c中实现了该类的构造函数rt_device_hwtimer_register，如下：

rt_err_t rt_device_hwtimer_register(rt_hwtimer_t *timer, const char *name, void *user_data)
{
    struct rt_device *device;

    RT_ASSERT(timer != RT_NULL);
    RT_ASSERT(timer->ops != RT_NULL);
    RT_ASSERT(timer->info != RT_NULL);

    device = &(timer->parent);

    device->type        = RT_Device_Class_Timer;
    device->rx_indicate = RT_NULL;
    device->tx_complete = RT_NULL;

#ifdef RT_USING_DEVICE_OPS
    device->ops         = &hwtimer_ops;
#else
    device->init        = rt_hwtimer_init;
    device->open        = rt_hwtimer_open;
    device->close       = rt_hwtimer_close;
    device->read        = rt_hwtimer_read;
    device->write       = rt_hwtimer_write;
    device->control     = rt_hwtimer_control;
#endif
    device->user_data   = user_data;

    return rt_device_register(device, name, RT_DEVICE_FLAG_RDWR | RT_DEVICE_FLAG_STANDALONE);
}

同样的套路，该类的构造函数主要是重写其父类(设备基类)的方法，硬件定时器的父类方法rtt写好了，

device->init        = rt_hwtimer_init;
device->open        = rt_hwtimer_open; 
device->close       = rt_hwtimer_close; 
device->read        = rt_hwtimer_read;   
device->write       = rt_hwtimer_write;