I have a problem that has defied me for a few days. Maybe someone else has seen this and has a solution.

I have an app that compiles fine. It is firmware for an instrument. I have ported it to FreeRTOS due to feature bloat and the RTOS allows more control over the symphony of tasks I now have.

The hardware is a generic STM32F103C with the STMDuino bootloader. Up to now this setup has worked very well with Visual Micro and I have numerous apps developed and working fine.

The FreeRTOS I am using is version 9 and is bundled with STMDuino. It was building and working well until I decided to change some tasks into timers. To do this it is necessary to make a few changes to definitions in "FreeRTOSConfig.h", to add "#include <utility/timers.h>", and to include "timers.c" in the build. This is all pure vanilla stuff and should take 5 minutes - here I am 3 days later and the build is still broken.

The app builds without errors and produces a binary. Sounds good - but - the linker throws a bunch of warnings about "undefined reference to xTimerCreate".

As I found out this is not a warning to be ignored. Running nm on Timers.o I find there are no symbols in it at all.

I am not inexperienced but after trying to track this down for days I cannot figure out what is going wrong. Clearly Timers.o is being built, the linker is linking it and producing a binary, but there are no functions in it. Of course the app is quite unlikely to work properly.

I suspect there is some "behind the scenes magic" going on or going wrong. Something is trying to make my life easier by doing stuff for me and not doing it well.

Any suggestions would be much appreciated. Thanks.
 
***** 3hrs later, after some more stuffing around, I have found the following;

I can get timers.o to build with symbols, but the app build still fails, this time with multiple definitions.

Here is how it works.

App specific definitions are in a local file "FreeRTOSConfig.h"
There is a define in this file which enables the timer functions. If it is set then there is stuff in timers.o

This file must be included before "MapleFreeRTOS900.h", which lives in the FreeRTOS folders. In this is an include for "FreeRTOS.h" which lives in the /utility folder, part of the FreeRTOS folders.

In this same folder is a template version of "FreeRTOSConfig.h". This is not the one I want to use. "FreeRTOS.h" includes this template version, but of course its contents should be ignored because it has an include protection and the local version has already been included.

What is actually happening is that the template version is being included.
Intellisense gets it right. If I view the local "FreeRTOSConfig.h" everything is enabled. If I view the template version it is all disabled. But the build process ignores all of this. It includes the template version and as a result none of the timers functions are built.

I proved this by setting the define for timers in the template version. "timers.o" was built with all its symbols and functions in it. Unfortunately there were lots of multiple definitions so the build failed.

So here is the question. xxx.ino has this at the top;

#include "FreeRTOSConfig.h"
#include <MapleFreeRTOS900.h>

The order of these includes is ignored by the build. The FreeRTOSConfig.h included by MapleFreeRTOS900.h is the one included and the local version is ignored.

This behaviour is not like any I have have experienced in many years of C programming. There is certainly some background magic happening. What?

Btw. Using VS2015, Arduino 1.6/1.8, Generic STM32F103C

Useful thanks.

I am a little confused by what you are saying but think this relates to the order of files in the link stage? Are you saying that local project code should be earlier in the linker list than libraries and core?

Either: 

Link project sources then lib sources then core

or

Link Core, lib source and then project sources

or something else?