Merge pull request cnlohr#698 from maxgerhardt/patch-7

Fix undeclared printf function usart_dma_rx_circular.c

Author: cnlohr

examples/usart_dma_rx_circular/usart_dma_rx_circular.c

@@ -2,6 +2,7 @@
 // Using any terminal, send "toggle\r\n" to control the LED connected to PC7.
 
 #include "ch32fun.h"
+#include <stdio.h>
 
 #define RX_BUF_LEN 16 // size of receive circular buffer
 
@@ -10,7 +11,7 @@ u8 cmd_buf[RX_BUF_LEN] = {0}; // buffer for complete command strings
 
 void process_cmd(u8* buf)
 {
-	if ( strncmp(buf, "toggle\r\n", 9) == 0) {
+	if ( strncmp((char*)buf, "toggle\r\n", 9) == 0) {
 		GPIOC->OUTDR ^= (1<<7);
 		printf("Horay!\r\n");
 	} else {