Adding an assembler source file to an mbed-os (5) project

I’m trying to add an assembly file to an mbed-os (5) project targeting the FRDM-K64F. The same main.cpp and my_asm.s files work fine with an mbed (2) project but with mbed-os (5) I get a fatal error
Error: Fatal error: A1023E: File “…/…/build/my_asm.K64F.E” could not be opened: No such file or directory
1 Error, 0 Warnings

I have got the in-line assembler to work OK on mbed-os projects but not using a separate .s source file.
Has anyone got a separate asm.s file to work within mbed-os (5) projects or has support been dropped for
separate assembly files within mbed-os (5)?

Best wishes,


Solved by ARM Technical support
The solution is to have a .S extension rather than a .s extension. In Keil you need to remove the file from the project and then re-add it having changed the extension to .S