LM3S5739 Datasheet, PDF (673/856 Pages) Texas Instruments – Stellaris® LM3S5739 Microcontroller

Stellaris® LM3S5739 Microcontroller
old address. As a result, the Host does not get a response to the IN request, and the Host
fails to enumerate the Device.
17.3.1.6
Device Mode SUSPEND
When no activity has occurred on the USB bus for 3 ms, the USB controller automatically enters
SUSPEND mode. If the SUSPEND interrupt has been enabled in the USB Interrupt Enable (USBIE)
register, an interrupt is generated at this time. When in SUSPEND mode, the PHY also goes into
SUSPEND mode. When RESUME signaling is detected, the USB controller exits SUSPEND mode
and takes the PHY out of SUSPEND. If the RESUME interrupt is enabled, an interrupt is generated.
The USB controller can also be forced to exit SUSPEND mode by setting the RESUME bit in the USB
Power (USBPOWER) register. When this bit is set, the USB controller exits SUSPEND mode and
drives RESUME signaling onto the bus. The RESUME bit must be cleared after 10 ms (a maximum
of 15 ms) to end RESUME signaling.
To meet USB power requirements, the controller can be put into Deep Sleep mode which keeps
the controller in a static state. The USB controller is not able to Hibernate because all the internal
states are lost as a result.
17.3.1.7
Start-of-Frame
When the USB controller is operating in Device mode, it receives a Start-Of-Frame (SOF) packet
from the Host once every millisecond. When the SOF packet is received, the 11-bit frame number
contained in the packet is written into the USB Frame Value (USBFRAME) register, and an SOF
interrupt is also signaled and can be handled by the application. Once the USB controller has started
to receive SOF packets, it expects one every millisecond. If no SOF packet is received after 1.00358
ms, the packet is assumed to have been lost, and the USBFRAME register is not updated. The
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,
November 17, 2011
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