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Spinpoint M8U-Internal Product Manual REV 3.4
62
INSTALLATION
remote wakeup signaling must be disabled.
6.3.6.1.7 Bus Enumeration
Before application can communicate with a device, the host need to learn about what transfer types and
endpoint the device support. The host also must assign an address to the device (Figure 6-29)
Figure 6-30: Enumeration
When a USB device is attached to or removed from the USB, the host uses a process known as bus
enumeration to identify and manage the device state changes necessary. When a USB device is attached to a
powered port, the following actions are taken:
1. The hub to which the USB device is now attached informs the host of the event via a reply on its status
change pipe. At this point, the USB device is in the Powered state and the port to which it is attached is
disabled.
2. The host determines the exact nature of the change by querying the hub.
3. Now that the host knows the port to which the new device has been attached, the host then waits for at
least 100 ms to allow completion of an insertion process and for power at the device to become stable.
The host then issues a port enable and reset command to that port.
4. The hub performs the required reset processing for that port. When the reset signal is released, the port has
been enabled. The USB device is now in the Default state and can draw no more than 100 mA from V
BUS. All
of its registers and state have been reset and it answers to the default address.
5. The host assigns a unique address to the USB device, moving the device to the Address state.
6. Before the USB device receives a unique address, its Default Control Pipe is still accessible via the default
address. The host reads the device descriptor to determine what actual maximum data payload size this USB
device’s default pipe can use.
7. The host reads the configuration information from the device by reading each configuration zero to n-1,
where n is the number of configurations. This process may take several milliseconds to complete.
8. Based on the configuration information and how the USB device will be used, the host assigns a
configuration value to the device. The device is now in the Configured state and all of the endpoints in this
configuration have taken on their described characteristics. The USB device may now draw the amount of
V
BUS power described in its descriptor for the selected configuration. From the device’s point of view, it is
now ready for use.
When the USB device is removed, the hub again sends a notification to the host. Detaching a device disables
the port to which it had been attached. Upon receiving the detach notification, the host will update its local
topological information.
6.3.6.2 Generic USB Device Operation
6.3.6.2.1 Dynamic Attachment and Removal
USB devices may be attached and removed at any time. The hub that provides the attachment point or port is
responsible for reporting any change in the state of the port.
The host enables the hub port where the device is attached upon detection of an attachment, which also has