ChromeOS Compatible - Docks Specification v2.0

Version: 2.0
Last updated: 2026-09-28

Overview

Dock types

This document covers docking stations that connect using USB-C to a Chromebook; KVMs are not within the scope of this document. These docking stations MAY include various types of video out support, including MST, charging pass through, and USB connectivity. Passive video dongles SHOULD follow the WWCB Video Dongle specification.

Minimum and Additional Requirements

This specification document is divided into two sections:

  1. Minimum requirements describe the criteria for a peripheral category to be compatible.
  2. Additional requirements describe the criteria for certification.

Use these navigation buttons to show only the minimum or both the minimum and additional specification, respectively.

Legend

Product Verb Development Action
"MUST" Mandatory product requirement
"SHOULD" Optional recommendation
"MAY" Nice to have

MINIMUM REQUIREMENTS

Generic peripheral Specifications

  • The peripheral MUST meet the minimum requirements defined in the Generic peripheral specifications.

Prerequisite Certifications

Electrical Design and Connectivity

Cables

  • Included cables MUST meet the minimum version of the connectivity standard supported by the dock.
  • All bundled cables MUST follow and pass Cable requirements for their respective associated cable type.

USB ports

  • If Vconn is used in a captive-cable design:
    • Captive-cable docks MUST accept and function with full range 3-5V Vconn.
    • An exception is allowed for TBT3 Certified docks, per Intel spec @ 4.25V.1

HDMI ports

  • HDMI ports that are HDMI SRC MUST provide Pin 18 +5V at 55mA, per the HDMI spec.
    • This voltage MUST NOT backfeed from improperly designed or noncompliant HDMI SNK devices (that improperly source voltage backwards on Pin 18).
    • The Dock MUST bidirectionally isolate Pin 18 to not cause malfunction in the preceding scenario.

Connectivity out

  • The dock MUST use a USB Type-C Receptacle Upstream Facing Port (UFP) (preferred) or Plug UFP.
  • The dock MUST meet minimal interconnect standards for each interface:
    • Each DP output MUST minimally support HBR2 clock rate.
    • Each HDMI output MUST minimally support 600Mhz TMDS clock rate.

Power

  • If the dock is self-powered only, the dock MUST include a power adapter that converts premises (AC) power to device (DC) power.
  • If the dock includes a power adapter, then the dock MUST conform to the guidelines in the Power adapter section.
  • If the dock is bus-powered with charge-through, then the dock MUST conform to following requirements:
    • The dock MUST comply with the following "Bus powered" section.

Power adapter

Internal adapter
  • The AC interface of the internal power adapter in the dock MUST use an IEC 60320 standard connector.
  • The internal power adapter MUST be 100-250v AC RMS input tolerant.

Bus powered

  • If the dock is a Charge-through dock, then the dock MUST conform to the following requirements for charge-through:
    • The dock MUST not pass through PDO objects without performing some sort of derating.
    • The dock MUST not pass through Fixed PDO objects without accounting for IR drop.
    • The dock MUST not pass through APDO PPS objects without internal reconversion.
    • The dock SHOULD drop APDO PPS objects presented by upstream power Source.

Overcurrent protection (OCP)

  • The dock MUST conform to the following requirements for Input protections:
    • The dock MUST not cause overcurrent event on Vbus or Vconn (1W or 1.5W source)2 due to the following causes:
    • Bulk inrush capacitance on Vbus
    • Enable activation inrush on Vbus
    • Bulk inrush capacitance on Vconn
    • Enable activation inrush on Vconn
  • The dock MUST conform to the following requirements for Output protections:
    • The dock MUST have overcurrent protection (OCP) on all source ports.
    • The dock SHOULD have dynamic D- or Type-C contract-based OCP limits.

USB

USB-C UFP (to ChromeOS device), a.k.a. Host port

  • The Host port MUST support DisplayPort AltMode.
  • The Host port MUST support USB Data.
  • The Host port MUST support USB Power Delivery.
  • The Host port MUST support DRP toggling.
  • The Host port MUST support a DRP state machine.
    • The Host port MUST support DualRolePower=1 bit (and respond to partner-initiated PR_SWAP with ACCEPT, REJECT, or non-infinite WAIT).
  • The Host port MUST support a DRD state machine.
    • The Host port MUST support DualRoleData=1 bit (and respond to partner-initiated DR_SWAP with ACCEPT, REJECT, or non-infinite WAIT).

USB-C DFP (to peripheral or charger)

The requirements in this section apply to each USB-C port on the dock.

  • The USB-C port MUST support BC1.2 DCP on all non-data charging ports.

USB and PD Behaviors

  • The dock MUST uniquely populate [USB Data Bus] VID + PID + bcdDevice.
    • The dock MUST match [USB-PD DiscoverIdentity + MfgInfo] responses verbatim.
  • If the dock is a complex collection of chips, the dock MUST use the Billboard endpoint as central target.
  • If the dock supports USB4 or Thunderbolt4, the dock MUST support multiple modes (USB4, TBT3, DPAM).
    • If the dock supports USB4 and not TBT4, then the dock MUST support USB4 and DP Alt mode v2.0 or later.
    • If the dock supports TBT4, then the dock MUST support USB4, TBT3 and DP Alt mode.
    • If the dock does not support USB4 and TBT4, then the dock MAY support DP Alt mode.
  • The dock MUST update USB-PD DiscoverIdentity Response and USB-PD DiscoverSVIDs and DiscoverModes and USB-Data (Billboard) fields in lock-step.
    • Descriptors in Billboard MUST match USB-PD data, USB data, and Physical device itself.
    • Any advanced modes listed using USB PD (USB4, Thunderbolt 3, DisplayPort Alternate Mode), MUST subsequently be listed in the dock's USB Billboard class device, See 3.1.6.2 Billboard Capability Descriptor, and Table 3-7.
    • The Billboard Capability Descriptor MUST list the same modes exposed by USB PD, with USB modes (such as USB4), and Alternate Modes, such as Thunderbolt 3 and DisplayPort Alternate Mode clearly listed, if supported by the dock.
    • URL string MUST be meaningful and accurate3
  • The dock MUST use correct DiscID and AltMode Discovery responses.
    • The dock MUST set Product Type (UFP) to PDUSB Hub (6.4.4.3.1.1.3 Product Type (UFP)).
  • The dock MUST respond with an appropriate SRC_CAP response.
    • Self-powered docks MUST mark UP=1.
    • If the dock has the capability to change from self-powered to bus-powered (i.e., a charge-through dock whose upstream power supply MAY be added or removed), then the UP setting MUST change to reflect (i.e., self powered MUST have UP=1, bus powered UP=0).
  • If the dock supports video-capable DisplayPort AltMode, then the dock MUST conform to the following requirements for pin config:
    • The dock MUST minimally support Pin Config C ( 4 = xxxxx1xxb = Pin Assignment C is supported).
  • If the dock supports USB3 Data-capable DisplayPort AltMode, then the dock MUST conform to the following requirements for pin config:
    • The dock MUST support Pin Config D ( 8 = xxxx1xxxb = Pin Assignment D is supported).

Either a manufacturer-specific permanently available URL, –or– the following VESA URL:
vesa.org/dp-usb-type-c
An example string is as follows: "DP-to-VGA adapter. For further assistance, see vesa.org/dp-usb-type-c."

Video

Prerequisite Certifications

  • If the dock implements DisplayLink, then the dock MUST pass the Synaptics DisplayLink Conformance test.
  • If the dock implements DisplayPort (DP), then the dock MUST implement VESA DisplayPort (DP) Standard version 1.4 or higher and pass the VESA DisplayPort Link Layer Compliance Test Specification for both DP input and output:
    • Section 6 - Branch Device Tests
    • Section 402 - Branch Device Tests in VESA DisplayPort Link Layer Compliance Test Specification: Extension Set 2 Version 1.2, Ext. 2
  • If the dock implements DisplayPort (DP), the following test suites in VESA DisplayPort PHY Compliance Test Specification for both DP input and output:
    • Section 6 - Hybrid Devices Compliance Tests for Type "T" (tethered) devices
    • Section 8 - Common Tests
  • If the dock support DP MST, the dock MUST pass test suite in Section 402 - Branch Device Tests in VESA DisplayPort Link Layer Compliance Test Specification:
    • Extension Set 2 Version 1.2, Ext. 2.
  • If the dock supports HDMI 2.0, the dock MUST comply with HDMI Specification Version 2.0, which includes passing the following test suites from HDMI Compliance Test Specification 2.1:
    • Section 3 - HDMI Connectors CTS 2.1
    • Section 4 - HDMI Source CTS 2.1
    • Section 4.2 and 4.3 - HDMI Repeater CTS 2.1
  • If the dock supports DP++, then the dock MUST be compliant with VESA DisplayPort Dual-Mode Standard Version 1.1 or higher.
    • The dock MUST pass the relevant tests from VESA DisplayPort Dual-Mode Cable Adaptor Compliance Test Specification for all non-DP outputs leveraging DP++.
  • If the dock supports HDCP, the dock MUST comply with the HDCP compliance report.

DisplayPort Input

  • When the dock is using a USB Type-C input, the dock MUST conform to the following requirements for DisplayPort AltMode:
    • The dock MUST minimally support DisplayPort AltMode Version 1.4 or later.
  • If the dock has a DP Sink (UFP_D) endpoint, the DP Sink endpoint MUST express proper pullup and pulldown on AUX- and AUX+, as follows:
    • AUX+ 1M pullup to 2.5-3.3v
    • AUX- 1M pulldown to GND
  • The dock MUST minimally support DP1.4 HBR3 display link training rates and protocol.

HDMI Outputs

  • If the dock implements HDMI and supports 4K display at 60Hz, then the dock MUST support HDMI 2.0.
  • The dock MUST not alter downstream EDIDs.
  • The dock's HDMI YCbCr state MUST be reset at every modeset.

DisplayPort Outputs

If the dock implements DisplayPort, then the dock MUST conform to the requirements in this section.

  • If the dock implements DisplayPort using a Type-C output, then the dock MUST conform to the following DisplayPort AltMode requirements:
    • The ports that support DP Alt mode on the dock MUST minimally support DisplayPort AltMode Version 2.0.
  • The dock MUST not use a second AUX sideband slot.
  • The dock MUST not alter downstream EDIDs.
  • The dock MUST minimally support DP1.4 HBR3 display link training rates.
    • This is to support Chromebooks with restricted lane count and bandwidth.
  • The dock's DisplayPort DP Source (DFP_D) originator MUST express proper pullup and pulldown on AUX- and AUX+, as follows:
    • AUX+ 10k-105k pulldown to GND
    • (Powered DP source) AUX- 10k-105k pullup to DP_PWR

MST

  • The dock MUST not alter downstream EDIDs.
    • This precludes EDID optimizations for blanking intervals.
  • The dock MUST comply with PD2.0 limits on VDM:Attention rate limiting.
    • The dock MUST limit PD2.0 MST VDM:Attention rate to 10ms.
    • The dock SHOULD limit PD3.0 MST VDM:Attention rate to 10ms.
  • The dock MUST support reconversion between 2-lane UFP_D and 4-lane DFP_D.
  • The dock MUST support reconversion between HBR3 links and HBR2 links.
  • The dock MUST support audio over MST.

HDCP

  • The display MUST support HDCP 1.4 or later.
  • If the display is a 4K display or greater, the display MUST support HDCP 2.2 or later.
  • The display SHOULD support the same HDCP versions on all inputs.

Audio

  • The dock MUST support Audio over HDMI when not using DisplayLink or Silicon Motion
  • The dock MUST use presence detection for 3.5mm jacks using UAC2 (or later)
  • The dock MUST support (for 3.5mm):
    • Both CTIA (LRGM) and OMTP (LRMG)
    • Headphone impedance > 16ohm
    • Headphone output level > 0.5Vrms, output power > 5mW
    • Frequency response up to 20kHz, passband ripple < ±0.5dB
    • SNR >= 90dB
    • THD+N <= -75dB
    • Crosstalk <= -60dB

ADDITIONAL REQUIREMENTS

Along with the Minimum requirements, a peripheral MUST meet the following mandatory requirements to achieve certification.

Generic peripheral Specifications

  • [Mandatory] The peripheral MUST meet the additional requirements defined in the Generic peripheral specifications.

Prerequisite certifications

  • [Mandatory] If the dock supports CEC over HDMI 1.4, the dock MUST pass the following test suites from HDMI Compliance Test Specification Supplement 1 Consumer Electronics Control:
    • CECT 7 - Electrical Specification
    • CECT 8 - Signaling and Bit Timings
    • CECT 9 - Frame Communication
    • CECT 10 - Device Installation and Addressing
    • Relevant feature tests from CECT 11
  • [Mandatory] If the dock supports CEC over HDMI 2.x, the dock MUST pass the following test suites from HDMI Compliance Test Specification 2.x:
    • Section 5 - CEC Device Test

Electrical Design and Connectivity

Firmware Update

  • [Mandatory] The dock MUST support firmware (FW) update.
  • [Mandatory] If the dock supports firmware update, then the dock MUST conform to the following requirements:
    • [Mandatory] The dock vendors MUST submit firmware to LVFS, which has different verification functions (e.g. fwupdmgr-verify-update).
    • [Optional] The dock vendor MAY also be needed to provide directly the firmware to Google ChromeOS team if requested.
    • [Mandatory] The dock MUST use fwupd for updating all the components inside the dock.
    • [Mandatory] The dock MUST NOT exclusively use proprietary FW update utilities or applications.
    • [Optional] The device boot SHOULD be blocked based on a key check (like a checksum that needs to match, for example). In addition, vendors SHOULD also provide a proper API to get the checksum.
    • [Mandatory] The firmware image MUST include, and with proper licensing for redistribution by Google.
    • [Mandatory] The device vendor MUST provide an MIT license file to enable firmware distribution from Google side to our devices.
    • This can be a plain-text license file bundled within the CAB file.
    • LVFS will also add support to upload the license file directly - tracked here.
  • [Optional] The dock SHOULD enable dual-partition (A-B) and silent updates, such that there is no user disruption during the firmware update process
  • [Optional] The dock SHOULD use [USB Data Endpoint Update] over USB Data wires to update its firmware.
  • [Optional] The dock MAY use various connection methods other than USB to update Dock firmware.

Power adapter

External adapter
  • [Optional] The AC-to-DC power adapter MAY be external to the case of the dock.
    • [Mandatory] The dock MUST deliver at least 27W to the ChromeOS device on the UFP USB-C connector using USB Power Delivery MUST comply with USB Power Delivery Section 10 Power Rules.
Internal adapter
  • [Optional] The AC-to-DC power adapter MAY be internal to the case of the dock.

USB

USB-A

  • [Optional] The dock SHOULD gain formal USB-IF Certification for Protocol and Phy.
    • SHOULD obtain informal results for components USB-IF Certification is prohibited or nonexistent (e.g. charge-through)

USB-C DFP (to peripheral or charger)

The requirements in this section apply to each USB-C port on the dock.

  • [Optional] If the USB-C port is power SINK only (i.e. no data, no power source out), then the USB-C port SHOULD be clearly marked as such.

USB and PD Behaviors

  • [Optional] The dock SHOULD retain USB Billboard Class enumeration if AltMode entry is completed successfully.
    • [Mandatory] The host device MUST keep the dock online, under the "Connection Successful" descriptor.
  • The dock MUST update USB-PD DiscoverIdentity Response and USB-PD DiscoverSVIDs and DiscoverModes and USB-Data (Billboard) fields in lock-step.
    • [Optional] Vendor ID SHOULD be Partner's name, OR chipset provider as a proxy (only if using the partner's name is infeasible).
  • [Optional] The dock SHOULD follow Unconstrained Power=1 PR_SWAP logic from PD spec.4
    • [Mandatory] The dock MUST propagate or mirror UP flag from power source (if power budget permits).
    • [Mandatory] If supported, the dock MUST propagate to SrcCapExt and Status fields accordingly.
  • [Optional] The dock SHOULD be tolerant of DP:Status 0x000000 DFP_D devices.
    • To support legacy Chromebooks (which do not populate this flag during the Discovery process).

Video

DisplayPort Input

  • [Optional] The dock SHOULD be tolerant of "unpowered DP SRC" signaled using AUX pulls.
    • This is to support legacy Chromebooks (which MAY contain excessively weak pulldowns).
    • Do not confuse "3.3v on Pin20 DP_PWR" with "DP SRC presence".

HDCP

  • [Optional] The display SHOULD have no discernable flicker (0 frames) when HDCP is enabled or disabled

Audio

  • [Optional] The dock SHOULD support Audio over DP when not using DisplayLink or Silicon Motion
  • [Optional] The dock SHOULD support, automatically detect, and report correctly connection of the following audio devices:
    • Mono mic
    • Stereo mic
    • Mono headphone
    • Stereo headphone
    • Mono headset (with mic)
    • Stereo headset (with mic)
  • [Optional] The dock SHOULD display the audio device only when plugged in.
  • [Optional] The dock SHOULD support the following button functions:
    • 3.5mm input
    • The dock SHOULD support the Android Headset standard on its 3.5mm input for both of:
      • 3-function remote
      • 4-function remote
    • The dock SHOULD support the Apple Headset standard on its 3.5mm input.
    • USB output
    • [Mandatory] The dock MUST support USB audio output using the HID command.

Revision history

Date Version Notes
2026-09-28 2.0 Remove draft warning, include cc-generic-peripheral, and apply _min_ext macro.
2026-09-02 1.0 Initial publication on partner site.

  1. See CAIRO spec "USB4™ Thunderbolt3™ Compatibility Requirements Specification" ↩

  2. Please refer to USB Type-C Spec "Vconn Sourcing Characteristics" regarding Vconn latch-off ↩

  3. See Vesa DP AltMode Specification V2.0 - 6.4 USB BB URL\ ↩

  4. PD3.2: 8.2.6 Use of "Unconstrained Power" bit with Batteries and AC supplies ↩