First we want to be able to talk to uboot, which is the board’s bootloader. Uboot communicates over uart4, which is described in the hardware page as “Dedicated UART header”.

 

You’ll need to connect the TXD, RXD, and GND pins to your usb-to-serial connector. On my FTDI-based connector, these connect directly — TXD to TX, RXD to RX, and GND to GND. If you are using something else as your usb-to-serial (such as an Arduino), you may need to switch the TXD and RXD cables.

 

Once you have connected your wires, plug the usb-to-serial cable in. This will create a device node. On the mac, for an FTDI-based board, this will show up as /dev/tty.usbserial-XXXXXXXX, where the Xs change for different boards.

 

I used GNU Screen as a serial terminal. From a terminal, type

 

 

… remembering to use the correct Xs, of course, and power up your CI20.

 

If all goes well, after a few seconds, you should see the CI20 load uboot. After another few seconds, you will see it load Linux. Eventually, you will get a terminal prompt and can log in (l/p ci20/ci20).

 

So now you have a “headless” ci20 setup, but that’s not so interesting, so shut the board down:

 

 

… and disconnect the power to the board (you can keep the usb-serial connected if you like). We’ll come back to it when we have something for it to run.

 

If you’re using GNU Screen, you can get back to a terminal by pressing ctrl-A k, that is, holding ctrl, pressing A, releasing both keys, and then pressing k. It will ask if you’re sure. You are. :) First stage complete!

 

 

Things get a bit tedious in this step. You’re going to compile gcc and friends for MIPS. On a Mac, this involves creating a case-sensitive disk image, using crosstool-ng to compile everything, and then installing and setting up a PATH. (On Linux, it’s the same process, but you don’t have to create a disk image).

 

(Update 2017: Doing this on a Mac has become significantly more tedious. The Homebrew version of crosstool-ng is broken, currently, and I also found that I needed a case-sensitive filesystem as the install target as well as for building. Actually, the compiler works just fine without being installed in a case-sensitive filesystem, so I ended up tricking crosstool-ng by mounting a case-sensitive filesystem over the target directory, building, then unmounting and copying the files. Unfortunately these new steps take the process from “tedious but doable” to “advanced”. Perhaps the solution is to switch to Clang.)

 

So, for the Macs: open Disk Utility and create a new disk image of at least a few GB. Make sure the image type is set to “Case sensitive”.

 

Mount the new image and cd to it, eg:

 

 

Now install Crosstool-NG. On a Mac, I recommend using homebrew:

 

 

Now we’re going to create the MIPS compilers. Start by setting up a big-endian MIPS template:

 

 

Now modify it:

 

 

We’re going to make two changes:

 

• In “Paths and misc options”, set “Prefix directory” to something sane. I picked /usr/local/mipsel-unknown-elf. If you do this, make sure you have write access to /usr/local/.
• In “Target options”, set “Endianness” to “Little endian” as that’s the endianness of the ci20 board.

Now select “Exit” (arrow right) until you return to your prompt. You can now build:

 

 

This will take a long time, but will, eventually, hopefully, complete without error. When this happens cd out of your case-sensitive disk image and unmount it. You won’t need it again and can throw it away if you like.

 

Now, add the tools to your path. The path you want to add is “bin/“ after whatever you set as “Prefix directory” above. So in my case, I added the following to my ~/.bash_profile:

 

 

Close and re-open your terminal if you changed your .bashrc, then test out your new compiler:

 

 

If you see GCC complaining in the above way, you now have a toolchain! The hard part is over.