Acer AC700 Chromebook
This page contains information about the Acer AC700 Chromebook that is interesting and/or useful to software developers. For general information about getting started with developing on Chromium OS (the open-source version of the software on Chrome OS devices), see the Chromium OS Developer Guide.
Caution: Modifications you make to the system are not supported by Google, may cause hardware, software or security issues and may void warranty.
Developer mode on the Acer AC700 has two levels of access, "dev-switch on" and "dev-mode BIOS". With the first level you enable a command line shell, which lets you look around inside the GNU/Linux operating system, but does not let you run your own versions. The second level of access installs a special BIOS component that provides the ability to boot your own operating systems from either removable (USB/SD) or fixed (SSD) drives. Both levels of access are completely reversible, so don't be afraid to experiment.
The developer switch enables the command line shell. The switch is underneath the chromebook battery. To enable the developer switch you remove the battery, use something pointy to move the switch towards the side with the red dot above it, and reboot. Note: be gentle! Some people have reported that the developer switch breaks easily. The first time you reboot after turning the developer switch on, your chromebook will:
- Show a scary warning that its software cannot be trusted, since a command line shell is enabled (press Ctrl-D or wait 30 seconds to dismiss).
- Erase all personal data on the "stateful partition" (i.e., user accounts and settings - no worries, though, since all data is in the cloud!).
- Make you wait between 5 and 10 minutes while it erases the data.
The erase and wait steps only happen when you first enable the developer switch, to help prevent someone from quickly reimaging your device while you're away from the keyboard. Successive boots will:
- Show the same scary warning (press Ctrl-D or wait 30 seconds to dismiss).
- Continue to boot only Google-signed images, and only from the SSD.
At this point, verified boot is still active but because a command line shell is enabled, your system is NOT secure. Refer to Poking around your Chrome OS Notebook to see how to access the command line shell. The message displayed at the shell itself should tell you how to set your own password to protect shell access and make your system secure again. Here's a photo showing the location of the developer switch:
If you want to make modifications to the Chrome OS filesystem or boot your own version of Chromium OS, you'll need to activate the second level of developer access. You do this by running a special command from the command line shell. You first log in with the username 'chronos' (if you've set a shell password, you'll be prompted for it). Then you switch to the 'root' account, and run the command to install the developer-mode BIOS. For example:
localhost login: chronos chronos@localhost $ sudo bash localhost chronos # chromeos-firmwareupdate --mode=todev
Verified boot is the process by which Chrome OS ensures that you are running only the software that shipped with your chromebook. The process starts with the read-only BIOS, which is built into the device at the factory and can't be modified without disassembly (please don't try that; you'll void your warranty). The read-only BIOS verifies one of two read-write BIOSes (there are two so we can provide updates if we have to with less risk of failure) and continues execution there. The read-write BIOS then verifies one of two (same reason) kernels and executes that, and the kernel verifies its root filesystem as each block is read off the SSD. The normal read-write BIOSes will only boot Google-signed kernels, and only from the SSD. When you run the chromeos-firmwareupdate command above, you are replacing the primary read-write BIOS with a different one that will allow any self-signed kernel (refer to the Chromium OS Developer Guide) to boot from either a removable device (by pressing Ctrl-U at the scary boot screen) or from the SSD (press Ctrl-D or wait 30 seconds).
- Follow the steps above to turn on the developer switch and to install the developer-mode BIOS.
- Build a Chrome OS image using the steps in the Chromium OS Developer Guide. It does not need to be a recovery image.
- Insert the removable drive containing your image into the left side USB slot.
- If you use the one on the right, the USB stick's light will flash, but the screen will stay black and the machine won't boot.
- Reboot, and when you see the blue scary boot screen, press Ctrl-U.
- It should boot your image. If for some reason it doesn't think your image is valid it will just beep once instead.
If you follow the full instructions from the Chromium OS Developer Guide, you will eventually end up with a bootable USB drive containing your image. You can boot that image directly from the USB drive as described above. Since it's your personal image, it should have shell access enabled. Log in as user "chronos" and run
That will wipe the SSD and install your image on it instead. When you reboot, it should attempt to boot your version. You'll still continue to see the scary boot screen at every boot, of course, as long as you are in developer mode and have the developer-mode BIOS installed, so you'll need to press Ctrl-D or wait 30 seconds to boot.
To leave developer mode, simply flip the developer-mode switch back to the OFF position and reboot. One of two things will happen. If your chromebook still has a valid read-write normal-mode BIOS, Google-signed kernel, and an unmodified Chrome OS root filesystem, then that's what will boot and you'll be back running the official Chrome OS image. Or, if you've modified any part of the verified boot chain so that a full verified boot process isn't possible, you'll be dropped into recovery mode. That will require you to create a bootable USB key to restore your chromebook to its fresh-from-the-factory state. That's annoying, but not dangerous. As long as you haven't taken the device apart, you shouldn't be able to permanently break anything. In either case, all personal information will be wiped from the device during the transition.
When the developer switch is on, the BIOS is not updated by any automatic Chrome OS updates. If you don't think you changed anything but you still end up in recovery mode, it may be that you've haven't applied a pending firmware update. Turn the developer switch back on, reboot, and from a root shell run
chromeos-firmwareupdate --mode tonormal
That will restore the primary read-write BIOS to normal mode, which may restore the verified boot process. Turn the developer switch off again and reboot. If you still end up in recovery mode, you'll just have to use the recovery process to fix it.
Recovery mode is a special boot operation in which the BIOS will:
- Refuse to boot from the SSD
- Prompt you to insert a recovery USB drive
- Only boot a Google-signed image from the USB drive
You will encounter recovery mode when the BIOS is unable to find a valid kernel to boot, either because the SSD has become corrupted or (more likely) because you modified all the kernel partitions while in developer mode and have switched back to normal mode. While in developer mode, you will be presented with the scary boot screen at every boot. Pressing SPACE or RETURN will take you to recovery mode.
You can also force your chromebook into recovery mode (even in normal mode) by using the recovery mode button. On the bottom of the Acer AC700 on the side nearest the Enter key, there is a tiny pinhole:
If you stick a paperclip into this hole, you'll feel it press a button. To force recovery mode, turn the device off, press this button, and while keeping it pressed, turn the device on again. This sometimes requires three hands or a bit of contortion, but you'll know it worked when you see the recovery screen instead of booting normally.
See the H2C firmware page for more details.
WARNING: Opening the case and fiddling with the stuff inside could easily brick your system and make it unrecoverable. DO NOT ATTEMPT if you are not familiar with this process.
Taking apart your laptop is not encouraged. If you have hardware troubles, please seek assistance first from an authorized center. Be advised that disassembly might void warranties or other obligations, so please consult any and all paperwork your received first. If you just want to see what the inside looks like, gaze upon this (click for high res versions):
However, we acknowledge that some people like to tinker. So here's a quick guide to taking it apart.
This is very easy to do and gets you access to all the pieces you most likely care about:
- The hard drive is easy to remove & replace/upgrade
- It is a standard SATA port, the form factor only allows Sandisk's pSSD
- Once you remove the two screws, use the black cover tab to pull down & remove the module
- The memory slots is easy to access
- The system uses 204-Pin DDR3 SO-DIMM laptop memory
- The wifi module is easily removable (two screws)
- The RTC battery can be replaced
And here's the details:
- Get a smallish phillips head screw driver -- all screws can be removed with just this
- Shut the system down and close the lid
- Flip the laptop over so the bottom is facing up and the speakers are closest to you
- Remove the three screws in the middle (on the visible plastic piece)
- Use the tab on the right side of the plastic piece to pop it off
Check out the high res picture above for overview.
While it is possible to remove the motherboard entirely, there isn't much of a point. You can see a high res image of what it looks like above if you just want that.
If you really want to remove it, then here's how:
- Remove the 9 screws from the outer edges of the bottom of the case
- Flip it over and open the display
- The top & bottom of the case should be slightly separated so you can
now remove the keyboard
- There are no screws holding it in, just tabs along the top/bottom
- Slowly work it until you can pull it straight up through the top half of the case
- Remove all the visible screws that were under the keyboard (there are a bunch)
- Pull the top half of the case off from the bottom
- Remove all the visible screws from the motherboard (there are only a few)
- Pop the wires off of the wifi & cellular modem
- Remove the screws from both screen hinges
- Be careful as the LCD wire shouldn't really be removed
- Disconnect the speakers and led module (bottom left)
- Pull the motherboard out of the case