USB On-The-Go

Original Article ↗ Hacker News Discussion ↗

USB On-The-Go and USB‑C Power Delivery expose a tangle of edge cases around who is the “host,” who supplies power, and when roles can safely swap. Commenters describe real-world failures — phones charging power banks, laptops refusing to charge from certain batteries, Y‑cables that can’t work safely, toothbrushes that only charge via USB‑A — and trace many of them to incomplete or non‑compliant USB‑C/PD implementations rather than the spec itself. The thread broadens into frustration with the opacity and evolving complexity of USB standards and cables, contrasted with older, more predictable interfaces and with tools and docks that partially tame the chaos.

USB-C Power Delivery & Role Swapping

  • Commenters clarify that USB-C with PD supports independent data-role and power-role swaps; host/device and source/sink can change separately.
  • PD also supports “fast role swap” to change power direction (e.g., dock ↔ laptop) without interrupting data.
  • Others read the article as really saying: “USB-C without PD” cannot decouple host/device role from power source, unlike classic OTG.

Charging Quirks, DRP, and Non‑Compliant Devices

  • Multiple anecdotes of phones, power banks, and laptops choosing the “wrong” power direction (phone charging bank, or devices refusing to charge).
  • USB‑C to USB‑A adapters often “fix” charging because they force legacy 5V behavior and bypass PD negotiation.
  • Some small gadgets (toothbrushes, flashlights, vapes, Raspberry Pi 4) are criticized for broken or missing CC resistors or negotiation, requiring USB‑A–to‑C cables to charge reliably.
  • Dual Role Port (DRP) capability exists in the spec to allow dynamic source/sink switching (e.g., power banks, phones), but many products simply don’t implement it.

Y‑Cables, Hubs, and Docks

  • Spec‑compliant USB‑C Y‑cables don’t really exist; passive splitters generally just parallel lines and fail for mixed power+data use.
  • Proper solution is a USB‑C hub/dock with PD‑in and downstream ports, effectively acting like the old “Accessory Charging Adapter.”
  • Mixed experience when plugging phones into laptop‑oriented docks: some work (power, peripherals, video), others only partly or not at all.

USB-C Complexity & Frustrations

  • Several posters express frustration at USB version churn (USB 3.x naming, introduction of C, PD, alt‑modes) breaking or complicating hardware designs.
  • Others argue shifting complexity to hardware/firmware is appropriate to simplify user experience, but note this leads to many non‑compliant, undocumented behaviors.
  • Complaints that you can’t tell by eye what a USB‑C port or cable supports (power direction, data rate, video, etc.), unlike older interfaces.

Cable Testers & e‑Markers

  • Discussion of USB‑C cable testers: simple continuity checkers vs pricier tools that read e‑markers and validate PD/alt‑mode capabilities.
  • Debate over whether the higher price of advanced testers is justified for small‑run, niche tools.

OTG Use Cases & Legacy Nostalgia

  • Reminiscences of OTG for keyboards, storage, camera backups, and niche use cases (e.g., burning CDs from Android, null‑modem gaming).
  • Some lament lost “simple GPIO” style experimentation formerly enabled by parallel ports, now replaced by more capable but more complex USB.