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USB Type-C to HDMI Adapter


The USB Type-C to HDMI Adapter connects a USB Type-C plug to an HDMI receptacle. It enables users of any Chrome device that implements USB-Type C to connect to an HDMI display.

Hardware Capabilities

This adapter is an implementation of a USB Type-C DFP_D to HDMI Protocol Converter. It follows the requirements of section 4.3.1 of the VESA DisplayPort Alt Mode for USB Type-C Standard. In the VESA standard, refer to Figure 4-13: Scenario 3a.

It provides the following features:


For schematics, click here or see the attached file.

Firmware Source Code

The firmware is located In the Chromium Embedded Controller repository under board/hoho/ :

Building Firmware

Within your ChromiumOS chroot, the syntax is:

cd ~/trunk/src/platform/ec
make BOARD=hoho

Flashing Firmware

The firmware is normally flashed via the kernel, as part of the ChromeOS Auto-Update process. Payloads are located in /lib/firmware/cros-pd.

When the adapter is connected to a Chrome device, you can manually flash the read-write firmware as follows:

ectool --cros_pd flashpd 4 <port> /tmp/

The device must be in developer mode to run the ectool command. After running this command, the firmware is located in ~/trunk/src/platform/ec/build/hoho/ec.bin .

Connecting to the Adapter

Developers of devices based on this design may need to install an initial image by putting the STM32F072 into DFU mode. This can be done by asserting PD_BOOOT0 (TP11 in the schematic) and resetting the MCU. It can be helpful to attach a switch for this purpose on prototype devices.

Installing an image requires the dfu-util tools package on the Chrome device where the adapter is connected. To deploy dfu-util and copy the chromeos-ec image from within your ChromiumOS chroot, the syntax is:

emerge-${BOARD} dfu-util chromeos-ec
cros deploy $IP dfu-util chromeos-ec
scp ~/trunk/src/platform/ec/build/hoho/ec.bin root@${IP}:/tmp/.

where board-name is the name of the Chrome device, for example peppy, and host-IP-address is its IP address on the network.

The next step is to connect the adapter to the Chrome device in DFU mode and write a full image (RO + RW). On the Chrome device, the syntax is:

flash_ec --board=hoho --image=/tmp/ec.bin