microbit-dal: Added readme.md

This read me describes the process of getting the microbit environment working with yotta.
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James Devine 2015-08-14 17:29:00 +01:00
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# microbit-dal
## 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:
## Getting Started
### 1. Install Yotta
The first step is to get Yotta onto your machine, to do this follow the install guide [here](http://docs.yottabuild.org/#installing)
**Note: if you are on windows, dependencies will be missed as of 8/8/15, please use the helper script located [here](https://github.com/ARMmbed/yotta/blob/master/get_yotta.py).**
### 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.
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](http://srecord.sourceforge.net/).**
### 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.