If a PC is made of desktop line of processors, no DRD is available yet. Currently only a few products (notably the Intel SoC aka "atom cheery trail" family, and other mobile-oriented chips found in mobile phones) have this capability. The IO of these two controllers must be multiplexed at the USB port pins. However, to be a DRD Type-C device, it must have TWO USB controllers inside, one of xHCI (host controller interface), and another of "DCI" type - device controller interface. It does this flip-flop several cycles per second. The DRD port advertises its dual role by continuously switching its CC (communication channel) pins from 5.1k pull-down (signifying a USB device) to 56k-22k-10k pull-up (signifying USB host with different VBUS supply capability). To connect one Type-C device (one PC) with another Type-C USB device (or another PC) and expect some connectivity, at least one of the "Type-C link partners" must support so-called DRD - Dual Role Device.
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