USB On-The-Go

Original Article ↗ Hacker News Discussion ↗

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.