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请教链表代码理解问题

发布于 2019-11-21 17:48:54 浏览：1438 订阅该版

在研究stm32f407的I2S时发现有几个函数是官方写的，但是在手册和官方文档中没有找到出处，请官方能否忙里偷闲加入这部分内容，我将此部分源码贴出来请官方获知：
```c
/**
 * Audio Memory Node Manage
 */
struct rt_data_node
{
    char *data_ptr;
    rt_uint32_t data_size;
};

struct rt_data_node_list
{
    struct rt_data_node *node;
    rt_uint32_t size;
    rt_uint32_t read_index, write_index;
    rt_uint32_t data_offset;
    void (*read_complete)(struct rt_data_node *node, void *user_data);
    void *user_data;
};

int rt_data_node_init(struct rt_data_node_list **node_list, rt_uint32_t size)
{
    int result = RT_EOK;
    struct rt_data_node_list *list = RT_NULL;
    struct rt_data_node *node = RT_NULL;

list = rt_malloc(sizeof(struct rt_data_node_list));
    if (list == RT_NULL)
    {
        result = -RT_ENOMEM;
        goto __exit;
    }
    memset(list, 0, sizeof(struct rt_data_node_list));

node = rt_malloc(sizeof(struct rt_data_node) * size);
    if (size == RT_NULL)
    {
        result = -RT_ENOMEM;
        goto __exit;
    }
    memset(node, 0, sizeof(struct rt_data_node));

list->node = node;
    list->size = size;
    list->read_index = 0;
    list->write_index = 0;
    list->data_offset = 0;
    list->read_complete = RT_NULL;
    list->user_data = 0;

*node_list = list;

return result;

__exit:
    if (list)
        rt_free(list);

if (node)
        rt_free(node);

return result;
}

int rt_data_node_is_empty(struct rt_data_node_list *node_list)
{
    rt_uint32_t read_index, write_index;
    rt_base_t level;

level = rt_hw_interrupt_disable();
    read_index = node_list->read_index;
    write_index = node_list->write_index;
    rt_hw_interrupt_enable(level);

if (read_index == write_index)
    {
        return RT_TRUE;
    }
    else
    {
        return RT_FALSE;
    }
}

void wait_node_free(struct rt_data_node_list *node_list)
{
    while (node_list->read_index != node_list->write_index)
        rt_thread_mdelay(5);
}

int rt_data_node_write(struct rt_data_node_list *node_list, void *buffer, rt_uint32_t size)
{
    struct rt_data_node *node = RT_NULL;
    rt_uint32_t read_index, write_index, next_index;
    rt_base_t level;

level = rt_hw_interrupt_disable();
    read_index = node_list->read_index;
    write_index = node_list->write_index;
    rt_hw_interrupt_enable(level);

next_index = write_index + 1;
    if (next_index >= node_list->size)
        next_index = 0;

if (next_index == read_index)
    {
        rt_kprintf("[node]:node list full, write index = %d, read index = %d <br>", write_index, read_index);
        return -RT_ERROR;
    }

level = rt_hw_interrupt_disable();
    /* set node attribute */
    node = &node_list->node[write_index];
    node->data_ptr = (char *) buffer;
    node->data_size = size;
    node_list->write_index = next_index;
    rt_hw_interrupt_enable(level);

return size;
}

int rt_data_node_read(struct rt_data_node_list *node_list, void *buffer, rt_uint32_t size)
{
    struct rt_data_node *node = RT_NULL;
    rt_uint32_t read_index, write_index, next_index;
    rt_int32_t remain_len, copy_size;
    rt_uint32_t read_offset, data_offset;
    rt_base_t level;
    rt_uint32_t result = size;

level = rt_hw_interrupt_disable();
    read_index = node_list->read_index;
    write_index = node_list->write_index;
    rt_hw_interrupt_enable(level);

read_offset = 0;
    if (read_index == write_index)
    {
        result = 0;
    }
    else
    {
        do
        {
            node = &node_list->node[node_list->read_index];
            data_offset = node_list->data_offset;
            remain_len = node->data_size - data_offset;
            if (size - read_offset > remain_len)
            {
                /* Full*/
                copy_size = remain_len;
            }
            else
            {
                /* reamain buffer */
                copy_size = size - read_offset;
            }

memcpy((char *)buffer + read_offset, node->data_ptr + data_offset, copy_size);
            read_offset += copy_size;
            data_offset += copy_size;
            node_list->data_offset = data_offset;

if (data_offset >= node->data_size)
            {
                /* notify transmitted complete. */
                if (node_list->read_complete != RT_NULL)
                {
                    node_list->read_complete(node, node_list->user_data);
                }

level = rt_hw_interrupt_disable();
                read_index = node_list->read_index;
                write_index = node_list->write_index;
                rt_hw_interrupt_enable(level);

next_index = read_index + 1;
                if (next_index >= node_list->size)
                    next_index = 0;

level = rt_hw_interrupt_disable();
                node_list->read_index = next_index;
                node_list->data_offset = 0;
                rt_hw_interrupt_enable(level);

if (next_index == write_index)
                {
                    result = read_offset;
                    break;
                }
            }
        }
        while (read_offset < size);
    }

return result;
}

static void data_node_read_complete(struct rt_data_node *node, void *user_data)
{
    struct rt_device *dev = RT_NULL;

dev = (struct rt_device *)user_data;
    if (dev->tx_complete != RT_NULL)
    {
        dev->tx_complete(dev, node->data_ptr);
    }
}
```