LM3S5P3B Datasheet, PDF (857/1170 Pages) Texas Instruments – Stellaris® LM3S5P3B Microcontroller

Stellaris^® LM3S5P3B Microcontroller
Zero Length OUT Data Packets
A zero-length OUT data packet is used to indicate the end of a control transfer. In normal operation,
such packets should only be received after the entire length of the Device request has been
transferred.
However, if the Host sends a zero-length OUT data packet before the entire length of Device request
has been transferred, it is signaling the premature end of the transfer. In this case, the USB controller
automatically flushes any IN token ready for the data phase from the FIFO and sets the DATAEND
bit in the USBCSRL0 register.
Setting the Device Address
When a Host is attempting to enumerate the USB Device, it requests that the Device change its
address from zero to some other value. The address is changed by writing the value that the Host
requested to the USB Device Functional Address (USBFADDR) register. However, care should
be taken when writing to USBFADDR to avoid changing the address before the transaction is
complete. This register should only be set after the SET_ADDRESS command is complete. Like all
control transactions, the transaction is only complete after the Device has left the STATUS phase.
In the case of a SET_ADDRESS command, the transaction is completed by responding to the IN
request from the Host with a zero-byte packet. Once the Device has responded to the IN request,
the USBFADDR register should be programmed to the new value as soon as possible to avoid
missing any new commands sent to the new address.
Note:
If the USBFADDR register is set to the new value as soon as the Device receives the OUT
transaction with the SET_ADDRESS command in the packet, it changes the address during
the control transfer. In this case, the Device does not receive the IN request that allows the
USB transaction to exit the STATUS phase of the control transfer because it is sent to the
old address. As a result, the Host does not get a response to the IN request, and the Host
fails to enumerate the Device.
18.3.1.6
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.
18.3.1.7
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
January 20, 2012
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