Intel PXA255 manual When GPIOn and GPIOx are Different Pins, When GPIOn and GPIOx are the Same Pin

USB Device Controller

Figure 12-2. Self-Powered Device

USB 5V	5 V to 3.3 V				GPIOn
		470K
					GPIOx
			1.5K
USB D+					UDC D+
				0 ohm
				(optional)
USB D-					UDC D-
				0 ohm
				(optional)
USB GND					Board GND

12.4.1.1When GPIOn and GPIOx are Different Pins

The GPIOn and GPIOx pins can be any GPIO pins. GPIOn must be a GPIO that can wake the device from sleep mode. After a reset, GPIOx is configured as an input. This causes the UDC+ line to float. GPIOn is configured to act as an input and to cause an interrupt on a rising or falling edge. When an interrupt occurs, software must read the GPIOn pin to determine if the cable is connected. The GPIOn pin is set to a 1 when the cable is connected and a 0 when the cable is disconnected. When a USB connect is detected, software must enable the UDC peripheral and drive a 1 to the GPIOx pin to indicate to the host PC that a high-speed USB device is connected. When a USB disconnect is detected, software must configure the GPIOx pin as an input, configure the GPIOn pin to detect a wakeup event, and put the disconnected peripheral in sleep mode, if desired.

If software must put a peripheral in sleep mode, it configures the GPIOx pin as an input. This causes the UDC+ line to float, which appears to be a disconnect to the host PC. The peripheral is put in sleep mode. When the peripheral comes out of sleep mode, software must drive a 1 to the GPIOx pin to indicate to the host PC that a high-speed USB peripheral is connected.

12.4.1.2When GPIOn and GPIOx are the Same Pin

After a reset, GPIOn is configured to act as an input and to cause an interrupt on a rising or falling edge. When an interrupt occurs, software must read the GPIOn pin to determine if the cable is connected. GPIOn is set to a 1 when the cable is connected and a 0 when the cable is disconnected. If a USB connect is detected, software must enable the UDC peripheral before the host PC sends the first USB command. If a USB disconnect is detected, software must configure the GPIOn pin to detect a wakeup event and put the peripheral in sleep mode, if desired.

When GPIOn and GPIOx are the same pin, do not put a peripheral in sleep mode if the USB cable is connected to the device. During sleep, the USB controller is in reset and does not respond to the host PC. When it returns from sleep mode, the peripheral does not respond to its host-assigned address.

Intel® PXA255 Processor Developer’s Manual 12-11