Bus-Powered Device - Intel PXA27 Series Design Manual

Out of reset, GPIOn is configured as an input and programmed to cause an interrupt whenever a
rising or falling edge is detected. Software must read the GPIOn pin when an interrupt occurs to
determine if a USB cable is connected or not. GPIOn is driven high when a cable is connected and
returns to a low state if the cable is disconnected. If a USB cable is connected, USB D+ is pulled
high using the 1.5 K Ω resistor to indicate to the host controller that a fast USB client device is
connected. Software must enable the USB Client peripheral before the host sends the first USB
command.
Note: When the single GPIOn/x configuration is in use, never put the PXA27x processor into sleep or
deep sleep mode while the USB cable is connected to the USB client interface for these reasons:
•
During sleep and deep sleep modes, the USB controller is in reset and does not respond to the
host.
•
After sleep or deep sleep mode, the USB client does not respond to its host-assigned address
because the previously assigned address is not retained during sleep and deep sleep modes.
Use the following sequence to enter sleep mode when GPIOn and GPIOx are the same signal. The
software must:
1. Read the GPIOn pin to verify a USB cable is not connected.
2. Configure the GPIOn pin to detect a wake-up event.
3. Enter sleep mode.
When a USB cable is attached, detected, and the host controller notified as explained in the note,
the host assigns a USB address for the USB client using the USB reset command.
12.4.2

Bus-Powered Device

The PXA27x processor cannot support a bus-powered device model. When the host sends a
suspend command, the device must consume less than 500 µA (refer to Section 7.2.3 of the
Universal Serial Bus Specification Revision 1.1). The processor cannot limit its current
consumption to 500 µA unless it enters sleep or deep sleep mode. If it enters either of these reduced
power modes, all USB registers are reset and the USB client does not respond to its host-assigned
address.
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Intel PXA27x Processor Family Design Guide
'USB Client Controller
II:12-5