https://devzone.nordicsemi.com/f/nordic-q-a/46629/error-5-cannot-open-source-input-file-app_fifo-h-no-such-file-or-directoryhello ! I am using nRF51 SDK 12 and even when I add the library of app_uart_fifo on keil it can&#39;t find app_fifo.h. As the screenshot shows, it is please help for my final project and thaks a loten-USTelligent Community 13Tue, 30 Apr 2019 20:55:13 GMThttps://devzone.nordicsemi.com/thread/184644?ContentTypeID=1Tue, 30 Apr 2019 20:55:13 GMT137ad170-7792-4731-bb38-c0d22fbe4515:ace96337-f99e-465f-8f2d-9a44f7d35f5aawneil[quote userid="77986" url="~/f/nordic-q-a/46629/error-5-cannot-open-source-input-file-app_fifo-h-no-such-file-or-directory"]it can&#39;t find app_fifo.h[/quote] <p>Does that file actually exist at all?</p> <p>If it does, is it in a location covered by your include paths?</p><div style="clear:both;"></div>