Coreboot installation on Chromebook ASUS C201PA

Goal

In this manual I will try to explain how to install Coreboot (2018 year version) on the Chromebook ASUS C201PA (later referred in the manual simply as C201) with the Paper build system. At the time of writing up this manual (Q1 2018), Libreboot didn’t have any updated sources for this laptop, so I decided it would be better to use Coreboot.

Introduction

There exists a Libreboot Chromebook ASUS C201 installation guide, and I would suggest you to read that first for easier understanding and detailed insight about what we’ll be trying to achieve through this manual. The steps are not identical, you will actually be installing Coreboot, which is a different project, but it might give you some ideas first about similar hardware and software being used here. I suggest that you read more about the Coreboot project, before proceeding with the installation. First of all before proceeding with anything you should already have a working GNU/Linux operating system on the C201. This manual does not explain how to install a GNU/Linux distribution on the C201, so you will need to find this information elsewhere. At the time of trying out this Coreboot installation I had a working GNU/Linux Debian 9 Stretch operating system on the SD card and Chrome operating system on the eMMC internal flash drive. This is my review of the summary by Paul Kocialkowski’s sets of instructions. Paul is a Libreboot and Coreboot developer who was willing to assist me getting this properly installed on my computer. The summary of all performed commands is written into a text file, so make sure to double check that, because this website wrongly renders and displays some of the characters.

Requirements

  • Secondary laptop (the same laptop could also be used)
  • USB key
  • Thin piece of plastic (guitar pick) for laptop disassembly
  • Installation of additional programs “apt-get install flashrom gnupg”

Laptop disassembly instructions

First step that you need to do is removing the write protect screw, which is inside the laptop. Refer to the similar Libreboot manual to read more about it. First you need to unscrew 8 screws which are holding the laptop together. Two of them are below the plastic caps/stands. Use something like a sharp piece of plastic to slide below them and remove them. You will need to open up the chasis of the C201. Best thing that can help you with that is by using some very thin piece of plastic, something like a guitar pick would be good. I did not have that and have used a credit card which was already a bit too thick to slide inside. You need to divide the shiny silver upper part and the lower blue part of the C201 by placing a piece of plastic in between and sliding it all around the lower part of the laptop. Beware that inside the laptop are the plastic clips which are holding the two parts together so don’t go too deep with the piece of plastic, not to break those clips. When you manage to divide the bottom and upper part of the laptop you need to beware not to divide those two parts up completelly, because inside there are two striped connectors (one black wider one for keyboard and one white thin one for touchpad), so be carefull when detaching those straps not to tear them apart (you don’t really need to detach them, you can also line up the parts). When you have opened up the laptop put it into such position. Then you unscrew the inner screw which is being marked inside of the white circle on the photo. That screw is the write protection screw for Coreboot, so without it you will be able to install Coreboot. When that is done, just assemble the laptop back together by pushing both parts (shiny silver upper part and bottom blue part) and save the screw.

Installation

Boot into Chrome OS. You will need some storage to transfer the files from Chrome OS to your other computer, an USB key is fine. You need to be in Chrome OS developer mode. Log in as root user into Chrome OS. This is done with Ctrl + Alt + F1 (top right arrow). Sometimes the root doesn’t have the password set, so just use the enter key to bypass password. You should see a visible # as a prompt. Insert the USB key. It will probably automatically mount itself, in my case it has mounted under /media/removable/USBDRIVE . If the USB key doesn’t automatically mount, you will need to perform the mounting commands. You need to put a file (flash.img) on the USB key. Go to the USB key directory.

  • # cd /media/removable/USBDRIVE
  • # flashrom -p host -r flash.img

Copy file flash.img to USB key. Power off the computer and stick the USB key into another computer. Boot into your favourite GNU/Linux distribution. Install Paul Kocialkowski’s gnupg public key (fingerprint 01B7 0C5D 940C B63D 5FA6 12C2 84FD C1EA 8FEE 950C) for verifying the installer. Create a directory on the PC and copy file flash.img from USB key there. Run the following commands as normal user (non-root) on another computer:

  • gpg –recv-keys 8FEE950C
  • export DOWNLOAD_URL=http://jp.si/C201/paper-release-20180102/
  • wget “$DOWNLOAD_URL/tools/x86_64/libreboot-release/libreboot-release”
  • chmod a+x libreboot-release
  • ./libreboot-release prepare cros-scripts vboot-tools coreboot-depthcharge-veyron-speedy

You should see an output similar to this. Then continue with the following commands:

  • VBOOT_TOOLS_PATH=tools/x86_64/vboot/vboot-tools tools/x86_64/cros-scripts/cros-scripts/cros-firmware-prepare vpd flash.img extract vpd.bin
  • VBOOT_TOOLS_PATH=tools/x86_64/vboot/vboot-tools tools/x86_64/cros-scripts/cros-scripts/cros-firmware-prepare vpd images/coreboot/coreboot-depthcharge-veyron-speedy/coreboot.rom replace vpd.bin
  • cp images/coreboot/coreboot-depthcharge-veyron-speedy/coreboot.rom .

You should see an output similar to this. Copy coreboot.rom file to the USB key. Power up C201 again and boot into Chrome OS. Insert the USB key and go into USB key directory, then type as root:

  • # flashrom -p host -w coreboot.rom

You should see a message like this:

erasing and writing flash chip…..Verifying flash….VERIFIED

SUCCESS

Then check the output of the crossystem command

  • # crossystem | grep dev_boot

If you see:

dev_boot_usb=1 , dev_boot_legacy=0 , dev_boot_signed_only=0

Then it is OK to reboot the C201. And that’s it. Commands that can be used during the Coreboot boot menu are:

  • Ctrl+h = Pauses the screen
  • Ctrl+u = Boots the GNU/Linux distribution (default is ChromeOS)

Disclaimer

Be sure to read the disclaimer before proceeding with the installation.

Setting up ALSA on Chromebook Asus C201 Debian

ALSA – Advanced Linux Sound Architecture

After initial preparation of the bootable Debian images, I managed to boot into Debian from the SD card and run system upgrade and migrate the Operating System from Debian Jessie to Debian Stretch (current Debian testing release). The migration was successful. There are a few things that still require tuning on this laptop, one of them is the ALSA (Advanced Linux Sound Architecture) system. Before proceeding with ALSA settings, there are a few things worth mentioning. The default installation doesn’t provide the working ALSA subsystem, and it can be “unsafe” (see disclaimer on the bottom of this article) if you try using the sound system without the correct system configuration, as you might even damage or ruin the speakers. So to begin with the settings:

First we will install the base of the ALSA packages, alsamixer for tuning the settings and pavucontrol monitor for setting additonal pulseaudio values:

  • aptitude install alsa-utils alsamixergui pulseaudio pulseaudio-utils pavucontrol

We start with configuration of the ALSA values by using the “amixer” entries. It’s advisable to copy all these values inside the script, so they can be executed after reboot in case of configuration loss. We will be using program “amixer” with “-Dhw” parameter and “ROCKCHIPI2S” is the device name we’re setting up. You can ignore the error “shared memfd open() failed: Function not implemented” if it appears. It is something related to the Linux kernel settings, which cannot be alternated inside the current running kernel. Apply the settings below as root or use “sudo” from the user account.

amixer -Dhw:ROCKCHIPI2S cset name=’Left Speaker Mixer Left DAC Switch’ on
amixer -Dhw:ROCKCHIPI2S cset name=’Right Speaker Mixer Right DAC Switch’ on
amixer -Dhw:ROCKCHIPI2S cset name=’Headphone Left Switch’ off
amixer -Dhw:ROCKCHIPI2S cset name=’Headphone Right Switch’ off
amixer -Dhw:ROCKCHIPI2S cset name=’Digital EQ 3 Band Switch’ off
amixer -Dhw:ROCKCHIPI2S cset name=’Digital EQ 5 Band Switch’ off
amixer -Dhw:ROCKCHIPI2S cset name=’Digital EQ 7 Band Switch’ off
amixer -Dhw:ROCKCHIPI2S cset name=’Biquad Switch’ off
amixer -Dhw:ROCKCHIPI2S cset name=’Filter Mode’ Music
amixer -Dhw:ROCKCHIPI2S cset name=’ADC Oversampling Rate’ 0
amixer -Dhw:ROCKCHIPI2S cset name=’DMIC Mux’ DMIC
amixer -Dhw:ROCKCHIPI2S cset name=’MIC2 Mux’ IN34
amixer -Dhw:ROCKCHIPI2S cset name=’Right ADC Mixer MIC2 Switch’ on
amixer -Dhw:ROCKCHIPI2S cset name=’Left ADC Mixer MIC2 Switch’ on
amixer -Dhw:ROCKCHIPI2S cset name=’MIC2 Volume’ 20
amixer -Dhw:ROCKCHIPI2S cset name=’Headset Mic Switch’ off
amixer -Dhw:ROCKCHIPI2S cset name=’Int Mic Switch’ on
amixer -Dhw:ROCKCHIPI2S cset name=’ADCR Boost Volume’ 4
amixer -Dhw:ROCKCHIPI2S cset name=’ADCL Boost Volume’ 4
amixer -Dhw:ROCKCHIPI2S cset name=’ADCR Volume’ 11
amixer -Dhw:ROCKCHIPI2S cset name=’ADCL Volume’ 11
amixer -Dhw:ROCKCHIPI2S cset name=’Left Speaker Mixer Left DAC Switch’ on
amixer -Dhw:ROCKCHIPI2S cset name=’Right Speaker Mixer Right DAC Switch’ on
amixer -Dhw:ROCKCHIPI2S cset name=’Speaker Left Mixer Volume’ 2
amixer -Dhw:ROCKCHIPI2S cset name=’Speaker Right Mixer Volume’ 2
amixer -Dhw:ROCKCHIPI2S cset name=’Record Path DC Blocking’ on
amixer -Dhw:ROCKCHIPI2S cset name=’Playback Path DC Blocking’ on
amixer -Dhw:ROCKCHIPI2S cset name=’Speaker Left Switch’ on
amixer -Dhw:ROCKCHIPI2S cset name=’Speaker Right Switch’ on
amixer -Dhw:ROCKCHIPI2S cset name=’Speaker Switch’ on

After implementing these values, the sound system should be ready. Test if there is any sound coming from the speakers by playing a .wav file on your computer. You can do this with the program “aplay”. There is a short manual for soundcard testing.

  • aplay -vv soundfile.wav

If this command gives you a visualisation of playing graphics inside the terminal but not producing the actual sound from the speakers, you can continue with sound test outside of “pulseaudio” mode with:

  • pasuspender — speaker-test -c2 -twav -l3 -Dhw:ROCKCHIPI2S

This should produce the sound in your speakers by a voice saying “Front left (on the left speaker) and front right (on the right speaker)”. You should probably hear this. This means that the hardware itself works and it could also mean that the pulseaudio is doing something strange not to hear the sound by using “aplay”. Next thing you could try is using pavucontrol GUI, which is the main pulseaudio configuration tool. Look at the picture below and match your settings similar to it, focus on the “Output devices” section and make sure the output device is selected as your fallback device and that it is not muted. Start “pavucontrol” as root and a GUI will open a similar image like the one below:

Select the bottom output device where it says “ROCKCHIP-I2S Analog Stereo” click on the speaker button to mute it and then again to unmute the device (just to be sure) and click the green button on the right side where is the setting for setting default output device. This worked for me and I was able to hear the sound coming out from the speakers.

The last thing which you need to apply is storing the ALSA values permanently into the system which will also work after reboot.

You can do this as root just type:

  • alsactl store

Alternative thing if “alsactl store” doesn’t save the values for you, you can still save the settings for ALSA inside the script with:

  • alsactl –file ~/.config/asound.state store

Which you reload after reboot with:

  • alsactl –file ~/.config/asound.state restore

That’s about it.

Disclaimer

Be sure to read the disclaimer before proceeding with the installation.

Libreboot with Debian on Chromebook C201

libreboot logo
Libreboot logo made by Marcus Moeller (2014) – Creative Commons license CC0 1.0 Universal

A few months back I obtained a Google Chromebook Asus C201. It arrived preinstalled with Chrome OS as default operating system. This laptop was listed as one of the possible laptop models that can use Libreboot. Free Software developer Paul Kocialkowski has ported Libreboot to this Chromebook. Libreboot is a free BIOS or UEFI replacement (free as in freedom); libre boot firmware that initializes the hardware and starts a bootloader for your operating system. It’s also an open source BIOS, but open source fails to promote freedom; please call libreboot free software. Since I know Paul K. from the Internet, he helped me with the guidelines about creating bootable Debian image to be used on this laptop. In my next blog post I plan to describe how to successfully create these bootable Debian images. This laptop has three possibilities about using a secondary operating system.

  • First possibility is to install the system on internal storage and replace the default Chrome OS.
  • Second possibility is to use an external USB key and have it stored there and the
  • third possibility (which I have chosen) was to install Debian on the Micro-SD card.

With my current setup I prefer to keep Chrome OS on internal storage and I can select secondary booting method to boot up Debian from Micro-SD card. I used Debian stable (Jessie) image and afterwards I have upgraded to Debian testing (stretch) to use more recent Debian packages. Just a short info for people that don’t know about Debian. Debian has one of the best designed release methods amongst GNU/Linux distributions, and their “main” software pool contains only free software. The “main” pool is also the only software pool that I will use on this laptop. Currently there are no other suitable FSF authorised distributions that would run on this laptop, next possible ports will include the Guix system distribution and Paul Kocialkowski is working on porting the Parabola GNU/Linux-libre distribution. My goal is to use only free software on this laptop, but there are some limitations. First the BIOS needs to be replaced with Libreboot, and the integrated Wi-Fi chipset would only work with proprietary software. Therefore for this purpose I have purchased a free hardware replacement – Qualcomm Atheros external USB Wi-Fi card, that uses AR9271 chipset, which is known to operate with free software. The model of this access point card is Sophos AP 5 Rev. 1. More about the recommended steps will follow up soon …