[Dev] Chromebook C201 wifi

Denis 'GNUtoo' Carikli GNUtoo at cyberdimension.org
Tue Apr 2 13:08:57 GMT 2019

On Mon, 1 Apr 2019 16:51:47 +0100
Josh Branning <lovell.joshyyy at gmail.com> wrote:

> Hi just had a look and there doesn't appear to be an easy option,
> though there are a few things that could help in u-boot by the looks
> of things, I'm not too familiar with u-boot, and it would require
> probably require someone who would know what they were doing to
> really help.
> But I guess probably you'd need to compile u-boot, changing some
> stuff, like grepping for "uA", "uV", "max-current" , "max-current"
> etc. have a look at arch/arm/dts and see what's going in there etc.
> Probably there is a main voltage regulator and a usb voltage
> regulator, someone who knows about electronics could tell you if it
> could be a problem with either, or just one or the other.

The best way to do that is to try to understand which chips are
involved in the power management in that chromebook and try to find
documentation on it.
- Start by looking at the devicetree of the device, as it describes the
  hardware that cannot be automatically detected.
- Then try to find some documentation on the chips involved in the USB
  voltage. Documentation can be found:
  - in the datasheet/reference manual of the respective chips if they
    are available online.
  - In Linux/u-boot/coreboot/depthcharge/chrome-ec Documentation or
    source code

Also when grepping you could look for the following:
- vbus: it's the USB 5v
- buck boost converter: it's a kind of voltage regulator that raises
  the voltage for instance from 3.3v to 5V.

As I understand the C201 uses the following free software projects:
- The EC source code is free software, so some information
  might also be in chrome-ec[1].
- It also uses Coreboot, but I don't know which payload u-boot chose to
  use. It's probably depthcharge according to the kernel install
  script, so it might also be interesting to look into that.


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