TM4C1294NCPDT:TI RTOS Unresolved symbol

Hello,

I don't understand when I would like to use a ring buffer function from #include "utils/ringbuf.h"

The compiler is OK but the error is in the linker.

However, the lib is ringbuf is include. 

Where is the problem ? 

Thanks in advance

Best regards 

Christophe GG