Samsung S5PC100 User Manual page 807

S5PC100 USER'S MANUAL (REV1.0)
3.1.5 Power Management
The Open Host Controller Interface Specification for the USB defines a port power-switching mechanism.
•
All ports are continuously powered, or the power is switched.
•
Power switching is switched globally for all ports or individually switched.
The power switching is independent of the port state, such as its speed, or whether it is connected or enabled.
Power-enable features operates only while the USB host clocks are running (the USB clocks must be running to
disable or enable power-enable features). This USB host controller has the following features that support power-
conservation features of the Open Host Controller Interface:
•
USB clock stopping
•
Port power-enable
3.1.6 USB Clock Stopping and Power Enable
The USB clocks can be stopped at any time; however, stopping the clocks is recommended if the USB is in the
global-suspend state, which is reached if there has been no activity on the USB for more than 5 ms, and the host
controller is in the suspend state. In the suspend state, the port (single-ended receivers on the USBH_P and
USBH_N pads) is also in low-power mode, but is still able to detect the USB port resume condition and
asynchronously generate an interrupt to the wake-up controller of the clock unit.
If a device is not connected to the USB port, the host controller cannot be suspended, and the port (PAD) is not in
its low-power mode. To save power if a device is not connected to the USB port (PAD), the port power enable can
be disabled before the USB clock is stopped (Refer to OHCI specification).
3.2 PROGRAMMING GUIDES
Programming the USB host controller is very similar to programming the USB host in S3C2443. The major
exceptions are in the base address of the OHC registers.
3.2.1 USB Reset
The USB host controller is not fully reset following a S5PC100 processor reset. The full-chip processor reset
leaves the USB force host controller reset bit set. To initialize the USB host controller, use the following sequence:
1. Start the USB clocks
2. Wait at least 10 µs
3. Force HC to Reset
The USB host controller is then operational.
3.2.2 USB Suspend
The USB specification defines a power-conservation mechanism called UsbSuspend. Devices and hubs is placed
into a suspend state; and if required, the whole system is suspended (global suspend). A USB device enters the
suspend state if it does not receive an SOF (keep awake) packet in greater than 3 ms. Software needs to
explicitly invoke the suspend state; otherwise, devices automatically receive 1-ms "keep-awake" SOF packets. If
there is no USB activity, the host invokes the global suspend state, which causes all connected devices and hubs
to enter into their suspend states within 5 ms.
USB HOST CONTROLLER
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