World first: C# kernel running on MIPS

Exciting news today as we announce our working kernel for MIPS based on the Creator CI20 board.

To the best of our knowledge, this is the first time in the world that anyone has got a C# kernel or operating system (of any form) working on a MIPS processor.

How did we do it?

We started the week by setting up the environment in which we were able to send a kernel binary file to the CI20. To see how this setup process is done, please read Ed’s post published earlier this week. After the connections were established we started to implement the necessary IL operations for the MIPS architecture to get the test kernel working.

The conversion of IL implementations from x86 to MIPS has been relatively smooth, except for the fact that in the MIPS architecture data stored in the memory must be half- or full-word aligned. This caused some initial headaches, however, Ed was determined to get to the bottom of the issue and in little time the problem was solved.

Other differences that required a lot of study and thought were related to the assembly code syntax for MIPS (GNU assembler – GAS) and the instructions available (reduced instruction set for MIPS). Although MIPS is a RISC architecture, meaning that more instructions must be used to perform the equivalent computation compared to x86, there are 16 general purpose registers available (as opposed to 4 on the x86) which makes implementation much easier. Furthermore, the programmer can also make use of pseudo-instructions which speed up implementation.

What does it do?

So what does the test kernel actually do? The answer is both not that much and quite a lot.

Although the functionality of the kernel is limited to changing the colour of the on-board LED and reading/writing characters from/to the UART ports, the fact that the kernel does that much proves that the FlingOS compiler is in a stable and solid state. It is a great proof of concept and initial step from which the new MIPS kernel can progress.

This has been a very exciting week and we are looking forward to completing the target architecture library and expanding the test kernel. In a few weeks time we will have a fully functioning IL compiler for MIPS.

Can I try it?

We’ll be releasing a compiler package and stable copy of the test kernel in the next month. We’d like to expand our compiler and proof-of-concept, test kernel a bit before releasing it to the wild.

Keep an eye on this space! Please ask questions below.

Ed and Roland

Stage 2 : Boot a custom OS

Earlier this week I tweeted that “Stage1: Boot a different OS – complete” meaning that I had successfully booted an alternative OS on the Creator CI20s (which were kindly provided by our sponsor Imagination Technologies®. Well, today I succeeded in booting a very basic custom operating system on the CI20s, so here’s how I did it.

For starters, I downloaded and installed the current compiler toolchain for Windows – Sourcey Codebench for MIPS available here. I installed mine to a non-standard directory but it works just fine. We’ll come on to how to use it later.

I also downloaded and install Putty and Serva – both of which are necessary tools. Putty provides a console interface to the serial connection required to talk to the CI20’s U-Boot bootloader. Serva provides an easy way to set up a TFTP server on Windows. Both of these tools are free. Again, we’ll come on to how to use them later.

Lastly, I had to buy one small (cheap) bit of extra hardware – a USB to UART converter. Be aware that there are two chips widely used to produce these devices. One of them only supports Linux and version of Windows 7 and earlier. The other chip supports Linux and all current versions of Windows – so make sure you get the right one! I bought one for Windows 8.1 (i.e. the second type of chip) from Amazon (with one day delivery on a Sunday no less!). I ordered from 3C4u who use Amazon. (The first time I tried to order two of these the package never arrived. I re-ordered and they were delivered fine. Amazon gave me a refund and Prime subscription extension for the first order so I’m not complaining too much!)

For the custom OS I wanted to try out something which I knew worked. So I went online and found’s great series of tutorials on writing a custom CI20 OS. I cloned the Git repo and started following the instructions. For the USB to TTL chip I have, the tutorial is correct, you need to connect RXD on the converter to TXD on the CI20, and visa-versa for TXD on the converter and RXD on the CI20. To avoid having to use the power cable, you can also attach the 5V pin to abny of the CI20’s 5V_IN pins on the primary expansion header. The board will power on as soon as you connect the 5V pin so hold off until later for that! You’ll also need to connect an Ethernet cable to the same hub or switch your PC/laptop/WiFi hub is connected to – this will be so the CI20 can connect to the TFTP server.

After cloning the Git repo I ran across a few issues. The tutorials were written for Max/Linux and for if you compile GCC yourself. Since I installed Sourcery CodeBench , the Makefile was not set up to compile properly. I eventually worked out how to it so it works properly. Here is a copy of my make file:

AS=mips-linux-gnu-as -mips32

OBJS=start.o main.o

hello.bin: hello.elf
 $(OBJCOPY) -O binary $< $@

hello.elf: $(OBJS)
 $(LD) -EL -T -o $@ $+

%.o: %.[Sc]
 $(CC) $(CFLAGS) -EL -c -o $@ $<

 rm -f *.o *.elf *.bin

I combined this with a simple batch script called build.bat in the same directory as the Makefile which allows me to specify the path to Sourcery CodeBench’s bin folder, instead of other version of GCC which I have installed. The batch script looked like this:

@echo off
SET BD=C:\Users\Ed\Documents\Coding\C\2015\MIPS\Compiler\bin
@echo on

Where BD is set to the path to Sourcery CodeBench’s “bin” folder.

Having compiled the “hello.bin” file I proceeded to set up Putty and the TFTP server. Here are a series of images I took showing the process. By the time I was done entering the commands into Putty (also shown below), the CI20 showed the nice, purple LED as expected.

2015-08-02 - Putty Config
Putty configuration

For the Putty configuration shown above, remember to update the COM port name to the name of the COM port device on your computer. This can be found by opening Device Manager and looking under the Ports node of the tree.

Serva config
Serva config

For the Serva configuration shown above, remember to update the “TFTP Server root directory” to the same folder as your “hello.bin” file is in.

2015-08-02 - Putty Console
Putty console

For the commands to U-Boot, remember to replace the serverip “” and the ipaddr “” with values for your network. The IP should be the IP address of the computer which is running Serva (which can be looked up by doing “ipconfig /all” in a Windows command prompt on the server computer). The “ipaddr” can be any value you like but the first three parts must match the IP address of your server.

2015-08-02 - Serva Log
Serva log

If the boot completes successfully, you should see a Serva log similar to the one above. The LED on the CI20 should turn purple as shown below.

Final result
Final result

The future’s so bright, I gotta wear shades…

Welcome back to my weekly update on my journey through the wilderness of OS development.

I’ve had a very enjoyable and productive week. I am still in the training phase of my internship but I can tell you now, within a few weeks, once I know enough about FlingOS, even more exciting things are going to be happening. Before I reveal more, let’s see what we’ve done this week.

Assembly to C

We have started the week by converting blocks of assembly code into C for the purposes of the upcoming tutorials in the context of memory and interrupts. The reason for this is that in the tutorial videos, equivalent implementations of the different development phases will be provided in three different languages; assembly, C and C#. This will be useful in seeing how each steps can be developed using the different languages, therefore you can decide which implementation suits your needs best.

We started by setting up the page directory and the page tables for the purposes of virtual memory management. Once that was achieved (after some frustration with pointers on my part) we set up memory to contain the kernel in the higher-half of the virtual memory space. This has advantages later when multiprocessing is desired. I learned about how to combine C code with assembly by the use of global procedures and data types as well as how one can use inline assembly to inject machine code directly into a C program. Mixing C with assembly can be useful as the implementation of certain tasks can be more straightforward in a high-level language. We have also spent some time setting up the Interrupt Descriptor Table entries in C. By working on this task with Ed, I learned, amongst other things, that the programmer can specify custom bit sizes for data types by using bitfield operators.

Getting to grips with C#

The second half of this week was spent on familiarising myself with C#. For this purpose, I have been looking at online tutorials on TutorialsPoint and on the Microsoft Developer Network site. I enjoyed learning about C#. It seems like a cool language to learn. I particularly like the documentation comment feature of the language. I think it’s very neat that you can leave comments in your code which then can be compiled into professional looking XML documentation resources. I also like the fact that C# is a type-safe language, so no need for pointers (yay from me). On the other hand, if you need to use pointers, you can declare “unsafe” blocks in your code where you can make use of them.

Plans for next week

Next week, I am going to be learning about the structure of the FlingOS compiler. I will be familiarising myself with the internal workings of the compiler by tweaking different parts of it and observing the output it produces. I will be able to put my newly found C# knowledge into good use since the compiler is written in this language. I will also be looking into how the compiler translates C# code into Intermediate Language code and how that IL code is translated into machine instructions. I am looking forward to tweaking the compiler to learn more about FlingOS and its internal workings. So, back to the exciting things I mentioned at the beginning of the post!

“Things are going great, and they’re only getting better”

Within the next few weeks, we are hoping to get started with porting a scaled down version of FlingOS onto our sponsor’s Creator CI20 development board. This means the translation of the existing x86 based code into code suitable for the MIPS32 architecture. A large part of the translation process involves converting CISC assembly instructions (x86) to RISC machine code used by MIPS32. Porting FlingOS onto the Ci20 board will be an exciting challenge and I will provide you with the details once we get started so you can consider developing your own OS on this great piece of kit.

That’s it from me, please come back next week for more info.


My first week as an intern!

This is the first of the weekly posts I am going to be sharing with you about my experience working with Ed during the 9 weeks of my summer internship. I will try to post as frequently as possible but I will produce a post at least once a week to let you know about the progress I make and the plans we have for the coming weeks. Before I say more about how the first week of my first ever internship has been, I thought I’ll introduce myself and my background (only briefly).


I was born in Hungary where I spent the first 19 years of my life living in Budapest. It is a great city to visit and there is a lot more to it than just eating Goulash :). In 2005, after finishing secondary education in Hungary I moved to the UK to learn English. I always wanted to study at university but as a 19 year old guy in a new country enjoying his freedom and doing what most 19 year olds want to do, I did not think much about going back to school. After some years working in a restaurant I realised that something was missing from my life, so I decided that I will pursue my childhood interest (which is, of course, computers). So I went to college to gain an IT Diploma after which I faced the biggest challenge of my life, studying computer science at university level. So here I am, a student at the University of Bristol starting my third year in September. Never been happier (and more exhausted)!

Never been happier (and more exhausted)!

My first week

These first few days with FlingOS have been very exciting. In only four days, I learned more about operating systems development than I did in my entire life. We covered topics, such as Booting, Initialisation, Memory Management and Interrupts. We have started to produce resources for the tutorial videos and articles which are planned to be released by the end of the summer so you can have a go at developing your own operating system as well. Producing the resources for the tutorials is a great way for me to learn about OS development. Most of the implementations we looked at are done in assembly language with which I’ve had some experience from previous university courseworks but definitely not at this level. Learning more about how to program in assembly is a great way of realising how the actual hardware works and how the computer is able to generate useful applications for the user from all those ones and zeros.

Future Plan

It is planned that I will be spending the first three weeks of the internship learning about FlingOS and OS development in general, mainly focusing on the x86 architecture on which FlingOS is based. At the end of the three week training period we will have the scripts with all the resources (code snippets, diagrams) ready so the production of the tutorial videos can be under way. The remaining six weeks will be spent on the development of FlingOS, more specifically writing device drivers using C#. I am really looking forward to the coming weeks to learn more from Ed and to make contributions to the project.

I would like to end this week’s post with a thank you to Ed for giving me the opportunity and taking me on-board, also a huge thanks to Imagination Technologies® for supporting the project and making this internship possible for me.

See you very soon and please check back for updates…

Sponsors FlingOS

Fantastic news this week as Imagination Technologies® has agreed to sponsor Fling OS to hire a student for Fling OS’s first ever summer placement. This is very welcome backing from a major player in both the UK and global low-level technology markets.

As part of the sponsorship deal I, Ed Nutting, will also be collaborating with Imagination Technologies and the University of Bristol to write and deliver a series of lectures focusing on teaching practical low-level and OS development. The lectures will run in the first term of the new academic year and will work alongside the Computer Science course to teach low-level development to second and third year students. The lectures will involve hands-on aspects making use of Imagination Technologies’ Creator CI20 and laptops kindly donated by the St Paul’s C of E Primary School, Enfield.

This will be a superb and exciting opportunity for Fling OS to make dramatic progress and to bring industry and education together to help students. This year’s summer placement students will be blogging here on this website so keep checking back!

Imagination Technologies and the Imagination Technologies logo are trademarks or registered trademarks of Imagination Technologies Limited and/or its affiliated group companies in the United Kingdom and/or other countries.