A universal serial bus, USB, port controller (120-1, 120-2) for interfacing a USB device through a USB port connector (102-1, 102-2), comprising: a communications interface circuit to communicate with a port manager circuit over a communications connection; and a control circuit configured to: switch operation of the USB port controller (120-1, 120-2) from a first power mode for normal operation of the USB port controller, to a second power mode for reduced power consumption by the USB port controller, in response to the communications interface circuit receiving a command (I2CIdle) from the port manager circuit, switch operation of the USB port controller (120-1, 120-2) from the second power mode to the first power mode in response to (i) detected activity on the communications connection, or (ii) a detected connection of a USB device to the USB port connector (102-1, 102-2), and characterized in that after switching from the second power mode to the first power mode in response to detected activity on the communications connection, to automatically switch operation of the USB port controller (120-1, 120-2) back to the second power mode unless a communications transaction addressed to the USB port controller is received within a non-zero time after switching from the second power mode to the first power mode. a communications interface circuit to communicate with a port manager circuit over a communications connection; and a control circuit configured to: switch operation of the USB port controller (120-1, 120-2) from a first power mode for normal operation of the USB port controller, to a second power mode for reduced power consumption by the USB port controller, in response to the communications interface circuit receiving a command (I2CIdle) from the port manager circuit, switch operation of the USB port controller (120-1, 120-2) from the second power mode to the first power mode in response to (i) detected activity on the communications connection, or (ii) a detected connection of a USB device to the USB port connector (102-1, 102-2), and characterized in that after switching from the second power mode to the first power mode in response to detected activity on the communications connection, to automatically switch operation of the USB port controller (120-1, 120-2) back to the second power mode unless a communications transaction addressed to the USB port controller is received within a non-zero time after switching from the second power mode to the first power mode. switch operation of the USB port controller (120-1, 120-2) from a first power mode for normal operation of the USB port controller, to a second power mode for reduced power consumption by the USB port controller, in response to the communications interface circuit receiving a command (I2CIdle) from the port manager circuit, switch operation of the USB port controller (120-1, 120-2) from the second power mode to the first power mode in response to (i) detected activity on the communications connection, or (ii) a detected connection of a USB device to the USB port connector (102-1, 102-2), and characterized in that after switching from the second power mode to the first power mode in response to detected activity on the communications connection, to automatically switch operation of the USB port controller (120-1, 120-2) back to the second power mode unless a communications transaction addressed to the USB port controller is received within a non-zero time after switching from the second power mode to the first power mode.