USB 3.0 Power States#
USB 3.0 defines four power states:
- U0: Normal operational state.
- U1: Receive and transmit circuitry quiesced.
- U2: Clock generation circuitry may additionally be quiesced.
- U3: Device is put into a suspend state. Significant link and device powers are saved, i.e., sensor, RAM, FPGA are disabled.
For the ace series, U0 will always be the default state and the camera will not suggest a suspend mode by itself.
Some host controllers are quite aggressive and try to use all states whenever possible. When a host suggests U1 or U2, the camera will not accept these modes and the host can not enter this low power state. This avoids extra latencies due to wake up times from camera or host.
However, when the host issues a U3 suspend which is usually related to a computer power suspend, the camera will follow this state.