Overview

I've recently been looking into the use of mbed for building embedded related projects. It turns out they've made building code against they're library very easy with a small tool called the mbed-cli. Mbed-cli is a python script that can be used to handle compiling / library dependency resolution / settings etc. for building projects.

I'm hoping that I might be able to get this working with Visual Micro at some stage so that I can single step / debug a board using GDB and a J-Link Segger or OpenOCD. For now, I've attempted to summarise most of the important bits when setting up and using the mbed-cli tool.

Installation

To get everything needed installed, we need to install the following.

They recommend using a gcc version of around 4.9 or so (although I've been trying stuff out with the latest one)

These are some of the links that relate to the install

Project system

Mbed has a concept of it's own project system that it uses via the mbed-cli tool

To create a new directory and set it up as an mbed project

mbed new mbed-os-program

To turn the existing current directory into an mbed project

mbed new .

Under the hood I think "mbed new" changes the directory into a git repository with "git init", then uses "mbed add" to add the mbed-os as the base library and I think a couple of other things.

To download and setup the example project blinky

mbed import https://github.com/ARMmbed/mbed-os-example-blinky

This is the same as a "git clone", followed by a "mbed deploy", followed by a "mbed new ."

Libraries

When using libraries within mbed there's two parts

  • A .lib file that registers that a library has been used within the project
  • A directory that contains the library files / code etc.

When checking code into git / source control the library directory is not checked in (just the .lib file). This way for a new user that downloads the source code they can run "mbed deploy" which is similar to Nuget restore. This reads in the .lib files downloads the library content and also resolves any dependencies for other libs that also have to be downloaded. This avoids having the actual library content sitting in your git repository, and allows you to use custom versions of the library

  • mbed add checks for library dependencies and downloads any other libs required.
  • mbed remove cleans up any .lib files left over when a library is removed

Example

mbed add https://developer.mbed.org/users/wim/code/TextLCD/
mbed remove TextLCD

Listing libraries installed

mbed ls -a

Configuration

Mbed has several different ways of storing it's configuration which are just key value pairs

  • Global Settings (mbed config --global)
  • Local Settings (mbed config) - stored in the .lib files
  • mbed_settings.py file
  • options passed to mbed compile

There's also a mbed_app.json application configuration file which gets expanded into a set of Macros for the compiled application

The three important ones to be aware of are

For example

mbed config target LPC1768
mbed toolchain GCC_ARM
mbed config GCC_ARM_PATH "C:\Program Files (x86)\GNU Tools ARM Embedded\5.4 2016q3\bin"

To list all settings

mbed config --list

To set a value

mbed config ARM_PATH "C:\Program Files\ARM"

To unset a value

mbed config --unset ARM_PATH

Compiling

When compiling most of the options can be set via the configuration values above

it's also possible to override some of those settings such as

mbed compile -t LPC1768 -t GCC_ARM

Which triggers the compile but also overrides the target and compiler to use

  • Macros can be set with the -D option such as "-DUVISOR_PRESENT"
  • A build profile can be set with the --profile option such as "--profile mbed-os/tools/profiles/debug.json"

There are currently 3 build profiles Default, Debug and Small

Compile Options

  • -m Override the target board to use, such as LPC1768
  • -t Override which toolchain target to use, this can be GCC_ARM, ARM, IAR
  • --source Specify the source directory, the default is the current directory.
  • --build Specify the build directory, the default is BUILD/
  • --profile This selects the build profile / options to use for the compiler.
  • --library Compile as a static library, .a or .ar
  • -c Do a clean build / rebuild to build from scratch
  • -j Control the number of threads for compiling, default is 0 which uses the number of cores on the machine
  • --app-config Override the path to the application configuration file
  • --config Show the compile time configurations
  • --prefix Filters the output from --config
  • --supported Show list of supported platforms, toolchains
  • -v -vv Verbose Output

Example Build

mbed import https://github.com/ARMmbed/mbed-os-example-blinky
cd mbed-os-example-blinky

mbed config target LPC1768
mbed toolchain GCC_ARM
mbed config GCC_ARM_PATH "C:\Program Files (x86)\GNU Tools ARM Embedded\5.4 2016q3\bin"

# Example of setting for debugging and overriding the target
mbed compile -c -m LPC1768 --profile mbed-os/tools/profiles/debug.json

# End result will be in .\BUILD\LPC1768\GCC_ARM\mbed-os-example-blinky.bin