uart改回DMA模式，环形buffer初始化复位读写指针

Signed-off-by: huhui <huhui@sharkgulf.com>

Application/bsp/uart.c

@@ -41,7 +41,7 @@
 #define SHARK_UART1_rx_dma_clk			RCU_DMA
 
 // ================================================================================
-#define ENABLE_RX_DMA 0
+#define ENABLE_RX_DMA 1
 
 static u8 shark_uart0_tx_cache[SHARK_UART_TX_MEM_SIZE];
 #if UART_NUM==2

Application/libs/circle_buffer.c

@@ -8,6 +8,7 @@ static int circle_get_read_space(c_buffer_t *cbuff);
 void circle_buffer_init(c_buffer_t *cbuff, uint8_t *buffer, int16_t max_len){
 	cbuff->buffer = buffer;
 	cbuff->buffer_len = max_len;
+	circle_reset(cbuff);
 }
 
 void circle_reset(c_buffer_t *cbuff){

Application/libs/circle_buffer.h

@@ -19,7 +19,13 @@ typedef struct {
 
 //used by dma
 static __inline__ void circle_update_write_position(c_buffer_t *cbuff, int pos){
-	cbuff->w_pos = pos;
+	if (pos != 0) {
+		if (pos == cbuff->buffer_len) {
+			cbuff->w_pos = 0;
+		}else {
+			cbuff->w_pos = pos;
+		}
+	}
 }
 
 static __inline__ int circle_get_read_position(c_buffer_t *cbuff){