ringbuffer中的相邻帧数据并不是连接的，由于每一帧数据按照内存对齐方式存放，相邻帧数据会有几个字节的间隔。
说明uart数据结构体成员的作用。
typedef struct {
uart_port_t uart_num; /*!< UART port number*/
int queue_size; /*!< UART event queue size*/
QueueHandle_t xQueueUart; /*!< UART queue handler*/
intr_handle_t intr_handle; /*!< UART interrupt handle*/
uart_mode_t uart_mode; /*!< UART controller actual mode set by uart_set_mode() */
bool coll_det_flg; /*!< UART collision detection flag */
bool rx_always_timeout_flg; /*!< UART always detect rx timeout flag */
//rx parameters
int rx_buffered_len; /*!< UART cached data length */ 缓冲区中还没有读取得数据长度
SemaphoreHandle_t rx_mux; /*!< UART RX data mutex*/
int rx_buf_size; /*!< RX ring buffer size */
RingbufHandle_t rx_ring_buf; /*!< RX ring buffer handler*/
bool rx_buffer_full_flg; /*!< RX ring buffer full flag. */
uint32_t rx_cur_remain; /*!< Data number that waiting to be read out in ring buffer item*/ 从缓冲区读出一帧数据的长度
uint8_t* rx_ptr; /*!< pointer to the current data in ring buffer*/ 指向从缓冲区读出的一帧数据
uint8_t* rx_head_ptr; /*!< pointer to the head of RX item*/ 指向从缓冲区读出的一帧数据
uint8_t rx_data_buf[SOC_UART_FIFO_LEN]; /*!< Data buffer to stash FIFO data*/
uint8_t rx_stash_len; /*!< stashed data length.(When using flow control, after reading out FIFO data, if we fail to push to buffer, we can just stash them.) */
uart_pat_rb_t rx_pattern_pos;
//tx parameters
SemaphoreHandle_t tx_fifo_sem; /*!< UART TX FIFO semaphore*/
SemaphoreHandle_t tx_mux; /*!< UART TX mutex*/
SemaphoreHandle_t tx_done_sem; /*!< UART TX done semaphore*/
SemaphoreHandle_t tx_brk_sem; /*!< UART TX send break done semaphore*/
int tx_buf_size; /*!< TX ring buffer size */
RingbufHandle_t tx_ring_buf; /*!< TX ring buffer handler*/
bool tx_waiting_fifo; /*!< this flag indicates that some task is waiting for FIFO empty interrupt, used to send all data without any data buffer*/
uint8_t* tx_ptr; /*!< TX data pointer to push to FIFO in TX buffer mode*/
uart_tx_data_t* tx_head; /*!< TX data pointer to head of the current buffer in TX ring buffer*/
uint32_t tx_len_tot; /*!< Total length of current item in ring buffer*/
uint32_t tx_len_cur;
uint8_t tx_brk_flg; /*!< Flag to indicate to send a break signal in the end of the item sending procedure */
uint8_t tx_brk_len; /*!< TX break signal cycle length/number */
uint8_t tx_waiting_brk; /*!< Flag to indicate that TX FIFO is ready to send break signal after FIFO is empty, do not push data into TX FIFO right now.*/
uart_select_notif_callback_t uart_select_notif_callback; /*!< Notification about select() events */
} uart_obj_t;