• 0 Posts
  • 8 Comments
Joined 2 years ago
cake
Cake day: June 26th, 2023

help-circle


  • In fact, most manufacturers save money and don’t shield the cable, forcing half-speed USB 1.1, which is enough for all mice and keyboards - less than 50 kb/s of the available 6 Mb/s is required even for 240Hz polling. High-end mice might have USB 3.0 (9 pins instead of 4 in the plug) but there should be no practical difference between 3.0 and 2.0 speeds.

    When speed is enough, latency became an issue. Although with 8kHz poll rate (USB 2.0 half-speed and full-speed can only get 1kHz poll rate), the latency will be 125µs at least. But for USB 3.0, it gained two ways to improve latency: 1) it can send Bus Interval Adjustment Message to adjust latency to 13.333µs (around 75kHz); 2) it can switch to async mode. Host no longer poll the device, instead, the device notify host via ERDY.

    Of course, I don’t know how many devices utilized these features.