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

Easy PXE Network boot

I had been meaning to set up a network boot system for FlingOS for a while. Yesterday I finally got around to it and after several hours of trying different software and solutions, I finally found one which worked nicely.

I had been meaning to set up a network boot system for FlingOS for a while. Yesterday I finally got around to it and after several hours of trying different software and solutions, I finally found one which worked nicely.

There is a modest selection of software out there which will let you set up PXE Network booting. The majority of it focuses around Windows installation and updating. What I needed was a system that would allow me to switch on any network-connected laptop and have it boot the latest version of FlingOS that I just compiled on my PC or main laptop. FlingOS already uses Syslinux as its bootloader so it made sense to use the Pxelinux variant of Syslinux. Unfortunately, Pxelinux requires something that most PXE Server programs don’t support – something called the tsize command.

PXE relies on a combination of DHCP, Binl and TFTP to allow a PC to detect the availability of a PXE server and to retrieve the boot image(s). Pxelinux requires that the TFTP server supports the unusual tsize command. “tsize” allows Pxelinux to request the size of a file ahead of time i.e. before it starts to retrieve it.

After various attempts using Serva and other software, I came across TinyPXE. Finally something that would work. TinyPXE was written by a guy who needed a simple, effective, no-install solution to running a PXE server. Perfect. It even comes with support for Pxelinux, Grub and others. What’s even better, is that it can auto-load everything from a human-readable config file. So once you’ve worked out what setup you need, you can just put it in the config file and never have to worry after that.

Here’s a copy of the contents of my config file (config.ini):

;will over rule the bootp filename or opt67 if the client arch matches one of the below
;needed to tell TFTPd where is the root folder
root=G:\Fling OS\Fling OS\Kernel\Kernel\bin\Debug\DriversCompiler\ISO
;bootp filename as in
;alternative bootp filename if request comes from ipxe or gpxe
; altfilename=menu.ipxe
;start HTTPd
;tftpd=1 by default
;will share (netbios) the root folder as PXE
;will log to log.txt
;alternative bootp filename if request comes thru proxydhcp (udp:4011)
;any extra dhcp options
;my gpxe / ipxe dhcp options
;the below will be executed when clicking on the online button
;cmd=_test viagra vente libre belgique.bat
;if log=1, will log to log.txt

MIPS / CI20 Custom OS

Want to write your own OS for Imagination Technologies® CI20? Or just want to investigate making a custom OS for MIPS? I’ve found a blog that has some great, practical content:’s CI20 Bare-metal articles

The articles are written for people using Mac OSX but there’s sufficient information, when combined with the CI20 Wiki, for Linux and Windows users to get the project working. It also helpfully includes links to eBay for USB to Serial boards connecting wires.

Will we ever see FlingOS running on the CI20? Maybe but not for a little while yet. If anyone fancies having a go at porting FlingOS, by all means head over to the Join page!