One of the great advantage of using an ARM core as on my FRDM-KL25Z board is that I can leverage a lot of things from the community. And one big thing around ARM is CMSIS (Cortex Microcontroller Software Interface Standard). It is an industry wide software library for the ARM Cortex microcontroller. Using the CMSIS libraries and interfaces will make it easier to port applications within the ARM Cortex family.

CMSIS has evolved over time, and even has added an RTOS API (CMSIS-RTOS API). What is the most interesting for me now is the CMS-DSP part of it: a set of over 60 functions for fixed point and floating point library routines. So how to use it in my project for the ARM Cortex-M0+ on the Freedom board?

For this Tutorial I’m using the Eclipse based CodeWarrior for MCU10.3, the CMSIS version V3.01 and the ARM GNU build tools with the Freedom FRDM-KL25Z board. As steps are pretty generic, that should work for other combinations too.

Downloading CMSIS

CMSIS is provided free of charge by ARM from their Silver Portal. On that Self-Service Portal there is a ‘Downloads’ link, but downloads are only available after I’m registered.

The current release is V3.01 and downloaded in a zip file of about 44 MByte in size.

Installing CMSIS

To simplify things, I have the CMSIS zip file unpacked inside my workspace. It creates the folders ‘Device’, ‘CMSIS’ and a file with the version number:

Creating a Project

Inside the workspace, I create a project for my board using the File > New > Barboard Project wizard to create a GNU gcc project. This creates a default project for me:

Instead of writing my own example, I’m using one which is part of the CMSIS installation:

ARM provides many such examples. They are a great way to verify that they work properly in my application. One consideration with using the libraries is their stack consumption. If they work as the simple example, but not within my application, then typically I have not reserved enough stack space. At least worth a try.

An easy way to add this file to my project is to drag&drop it into my project Sources folder. As the example comes with a main(), I can remove the original main.c from my project:

Creating a Build Variable

We need to reference the CMSIS installation path in the next steps several times. To make things easier and more portable, I’m going to add a Build variable. For this I press ‘Add’ in the project properties > C/C++ Build > Build Variables:

In the following dialog I define my variable and press OK:

Of course you should use a path pointing to to where you have CMSIS installed. For me, it is is “c:\tmp\wsp_cmsis\CMSIS” in this tutorial, so you need to use the path which you have on your system.

With this, I can always use

${CMSIS_LOC}

instead of a hard-coded path.

Using CMSIS

The above project will not compile and link. I need to tell the compiler where to are the CMSIS header files, and what library to link.

Header File Include

The CMSIS header files are in CMSIS\Include, so I add this to my compiler include paths:

I’m using here the CMSIS library inside my workspace. Change the path if you have the CMSIS installed somewhere else.

Architecture Define

The other important thing is: I need to set a define which tells the CMSIS library which ARM Cortex core I’m using. For the ARM Cortex-M0+ this is ARM_MATH_CM0. I add this define to the project properties of the ARM gcc preprocessor settings.

If using an ARM Cortex-M4 (like for the Kinetis K family), then the define would be ARM_MATH_CM4

Library

CMSIS already comes with pre-built libraries. So all what I need to do for gcc is to link the correct libraries with my application. The libraries are inside CMSIS\Lib\GCC:

The M denotes the ARM core, while the ‘l’ means ‘little endian’. The ‘f’ means an ARM core with Harware Floating Point Unit (e.g. Cortex-M4F).

With this information, I add the library name and the library search path to my linker settings:

Important: the library name is *without* the ‘lib’ prefix and *without* the ‘.a’ suffix! See Creating and using Libraries with ARM gcc and Eclipse.

Build and Debug

With this, everything should be in place to compile, link and download without errors. But if I step into the CMSIS functions, I get a message from the debugger that it cannot find the source file:

The reason is that I’m using the precompiled libraries from ARM, and obviously that person was using a different path to the CMSIS library.

To help the debugger to find the source, I’m going to add a path mapping. I press the ‘Edit Source Lookup Path’ button:

Then I select Path Mapping:

Then I specify that ‘c:\working\CMSIS_Setup\CMSIS shall be replace with the path on my machine:

I would love to use my ${CMSIS_LOC} variable in that dialog, but this is not supported in this Eclipse version? That would be a great feature extension.

Now it shows the source properly:

Summary

Using the CMSIS from ARM is a great add-on to my applications: I can take advantage of DSP and other functionality without writing them myself. All what it needs is to set configure my project to use one of the precompiled libraries.

My current CMSIS library and application project are on GitHub.

Happy CMSISing