dma_channel_subperipheral_select函数中sub_periph参数

引用\[3\]中的代码片段是关于USART的头文件定义，其中定义了一些宏和函数。在这个头文件中，没有找到dma_channel_subperipheral_select函数的定义。所以无法提供sub_periph参数的具体含义和用法。请确认是否提供了正确的引用内容。
#### 引用[.reference_title]
- *1* *2* [GD32 RTC 调试之NVIC设置](https://blog.csdn.net/yangkunhenry/article/details/93194473)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v91^insert_down28v1,239^v3^insert_chatgpt"}} ] [.reference_item]
- *3* [RT-Thread 框架下，GD32F450，串口DMA收发驱动 编写示例](https://blog.csdn.net/qq_36720691/article/details/126712637)[target="_blank" data-report-click={"spm":"1018.2226.3001.9630","extra":{"utm_source":"vip_chatgpt_common_search_pc_result","utm_medium":"distribute.pc_search_result.none-task-cask-2~all~insert_cask~default-1-null.142^v91^insert_down28v1,239^v3^insert_chatgpt"}} ] [.reference_item]
[ .reference_list ]