Error: L6218E: Undefined symbol app_uart_init (referred from main.o).

HI:

Always error while porting,Error: L6218E: Undefined symbol app_uart_init (referred from main.o).

I added a path, and ENABLE  UART_ENABLE 1  in sdk_cofig.h

Compile signal main.c is  pass,but  compile all file is error.

Thanks