LM3S5652 Datasheet, PDF (667/848 Pages) Texas Instruments – Stellaris® LM3S5652 Microcontroller

Stellaris® LM3S5652 Microcontroller
USB controller continues and resynchronizes these pulses to the received SOF packets when these
packets are successfully received again.
17.3.1.8
USB RESET
When the USB controller is in Device mode and a RESET condition is detected on the USB bus,
the USB controller automatically performs the following actions:
■ Clears the USBFADDR register.
■ Clears the USB Endpoint Index (USBEPIDX) register.
■ Flushes all endpoint FIFOs.
■ Clears all control/status registers.
■ Enables all endpoint interrupts.
■ Generates a RESET interrupt.
When the application software driving the USB controller receives a RESET interrupt, any open
pipes are closed and the USB controller waits for bus enumeration to begin.
17.3.1.9
Connect/Disconnect
The USB controller connection to the USB bus is handled by software. The USB PHY can be
switched between normal mode and non-driving mode by setting or clearing the SOFTCONN bit of
the USBPOWER register. When the SOFTCONN bit is set, the PHY is placed in its normal mode,
and the USB0DP/USB0DM lines of the USB bus are enabled. At the same time, the USB controller
is placed into a state, in which it does not respond to any USB signaling except a USB RESET.
When the SOFTCONN bit is cleared, the PHY is put into non-driving mode, USB0DP and USB0DM are
tristated, and the USB controller appears to other devices on the USB bus as if it has been
disconnected. The non-driving mode is the default so the USB controller appears disconnected until
the SOFTCONN bit has been set. The application software can then choose when to set the PHY
into its normal mode. Systems with a lengthy initialization procedure may use this to ensure that
initialization is complete, and the system is ready to perform enumeration before connecting to the
USB bus. Once the SOFTCONN bit has been set, the USB controller can be disconnected by clearing
this bit.
When the USB controller is acting as a self-powered Device, a GPIO input or analog comparator
input must be connected to VBUS and configured to generate an interrupt when the VBUS level
drops. This interrupt is used to disable the pullup resistor on the USB0DP signal.
Note: The USB controller does not generate an interrupt when the Device is connected to the
Host. However, an interrupt is generated when the Host terminates a session.
17.3.2
Operation as a Host
When the Stellaris USB controller is operating in Host mode, it can either be used for point-to-point
communications with another USB device or, when attached to a hub, for communication with
multiple devices. Before the USB controller's operating mode is changed from Host to Device or
Device to Host, software must reset the USB controller by setting the USB0 bit in the Software
Reset Control 2 (SRCR2) register (see page 240). Full-speed and low-speed USB devices are
supported, both for point-to-point communication and for operation through a hub. The USB controller
automatically carries out the necessary transaction translation needed to allow a low-speed or
November 17, 2011
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