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I'm trying to get a concrete answer on what determines DRD support... the port type (USB-C) or the protocol type (USB 3.1). Besides the poor naming scheme with USB 3.0/3.1/3.2, there's a lot of lacking communication about the DRD device support (being able to act as a device or host).

According to https://blogs.synopsys.com/tousbornottousb/2018/05/03/usb-dual-role-replaces-usb-on-the-go it is any USB spec at or above 3.1, but it also confusingly talks about being Type-C

This Intel page talks about having DRD with USB 3.2 Gen 1x1 (5 Gb/s) with no mention of Type-C.

Wikipedia mentions DRD on their USB Type-C page, but not on their USB 3.1 page.

I'm trying to find some kind of authoritative answer on this question, if possible

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  • \$\begingroup\$ Wikipedia states "USB Dual-Role-Device capabilities introduced with the USB 3.1 specification". \$\endgroup\$
    – Finbarr
    Commented Mar 20, 2021 at 0:03
  • \$\begingroup\$ Right, but I believe USB 3.1 might be possible with a Type-A and Type-C connectors, but I'm suspecting Type-A may be incompatible with OTG / DRD. Ale's response below also suggests the same. \$\endgroup\$
    – Wisteso
    Commented Mar 20, 2021 at 3:36

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Dual-role USB ports were introduced in so-called "On-The-Go" (OTG) supplement to USB specifications. (still cannot figure out what OTG means). The role swap came at the expense of introducing one extra pin - ID pin. Therefore originally only mini- and micro-USB ports can provide the swap function, and Type-A can't provide the swap. Additional function of source-sink swap was provided at DC level, called "accessory charging".

Type-C Cable and Connector Specification is the next step in providing flexibility to USB. Type-C specifies new CONNECTOR, which can carry various data protocols, although originally it was supposed to be only USB. Thus the Type-C is the standart nearly independent from USB (or anything else), and USB2, 3.x or 4 don't matter.

Keep in mind that there are two basic roles of a port - power role, and data role. Since USB is a host-centric protocol, this distinction is quite important. So four combination of roles are possible. Type-C basic (DC-based) communication functionality (over CC pulls up-down) defines only the default swap function - either a host (and a power source), or a device (and a power sink). To provide two other configurations (host-sink and device-source), a negotiation over additional protocol is required. It is implemented within Power Delivery protocol over the same CC wire using serial communication messages.

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  • \$\begingroup\$ This is nicely explained. Just to confirm... this means Type-A can never be OTG / Dual Role? However Type-B, Mini, Micro, and Type-C are able? The power / data part makes sense, and that part was fairly clear, but I didn't know about the extra pin needed to facilitate swapping. \$\endgroup\$
    – Wisteso
    Commented Mar 20, 2021 at 3:34
  • \$\begingroup\$ @Wisteso, No, Type-B port is only for devices, and thus is not "swappable".. Mini and micro ports must be of dual "A/B" type to be "swappable", although the industry abandoned "A/B" and used only B-type receptacles in formal violation of OTG specs. \$\endgroup\$
    – Ale..chenski
    Commented Mar 20, 2021 at 15:36
  • \$\begingroup\$ Okay that makes sense. So basically Type-C is the only type that can flip between both then? (Due to non-conformance to OTG) Otherwise you have to be device-only (B, micro, mini) or host-only (A)? \$\endgroup\$
    – Wisteso
    Commented Mar 20, 2021 at 23:02
  • \$\begingroup\$ " (still cannot figure out what OTG means) " It was called "on the go" because it was built for use on portable devices. A device large enough for 2 USB ports would not need a dual role port since there is a port for both roles. It is a violation of the spec to have both OTG and more than 1 USB port. Large devices needing both roles, such as a printer that is a client to a computer and host to a flash drive, will not be expected to require disconnection from the computer to read files from the drive. Acting a USB client to 2 hosts is somewhat nonsensical as that is best by a network. \$\endgroup\$
    – MacGuffin
    Commented Jun 16, 2021 at 11:36

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