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Building a project for the micro:bit using Yotta

Instead of using the online IDE, Yotta can be used to provide an equivalent offline experience. The current compilers that are available are:

  • GCC

Getting Started

1. Install Yotta

The first step is to get Yotta onto your machine, to do this follow the install guide here

Note: if you are on windows, dependencies will be missed as of 8/8/15, please use the helper script located here.

2. Fetch the example project

If your install has gone correctly, and you have all dependencies installed, the next step is to fetch the example project using the runtime from GitHub.

git clone https://github.com/lancaster-university/microbit

Note: To successfully build this project you will need access to the microbit-dal private repository, if you need access please email me at j.devine@lancaster.ac.uk.

3. Try to build

Building rarely works first time due to dependencies currently not being installed by Yotta, so the next step is to try to build.

The default yotta target you will receive when you pull the aforementioned repo is bbc-microbit-classic-armcc, you can use the following command to print your current target in Yotta:

yt target

bbc-microbit-classic-armcc 0.0.5
mbed-armcc 0.0.8

If you do not have armcc installed (or don't have a license for Keil), then you will need to use GCC. To swap to the GCC target run:

yt target bbc-microbit-classic-gcc

Then you should try to build using the following command:

yt build

For GCC, you will have to swap the CortexContextSwitch.s file with the file CortexContextSwitch.s.gcc which will be located in /yotta_modules/microbit-dal/source. For an example of how to do this, look below:

#first rename the existing one
mv yotta_modules/microbit-dal/source/CortexContextSwitch.s yotta_modules/microbit-dal/source/CortexContextSwitch.s.armcc

#then rename gcc version so that it is included by cmake
mv yotta_modules/microbit-dal/source/CortexContextSwitch.s.gcc yotta_modules/microbit-dal/source/CortexContextSwitch.s

This is a temporary measure until Yotta supports assembly preprocessing for armcc.

NOTE: To build the final hex files for the micro:bit, you will need to install the srec which can be installed via brew (brew install srecord), or you can install it manually from here.

4. Flash your micro:bit

The final step is to check your hex works.

The yotta build command will place files in /build/<TARGET_NAME>/source. The file you will need to flash will be microbit-combined.hex. Simply drag and drop the hex.

The expected result will be that the micro:bit will scroll BELLO! :) on its display.