LM3S5739 Datasheet, PDF (672/856 Pages) Texas Instruments – Stellaris® LM3S5739 Microcontroller

Universal Serial Bus (USB) Controller
17.3.1.5
Additional Actions
The USB controller responds automatically to certain conditions on the USB bus or actions by the
Host controller such as when the USB controller automatically stalls a control transfer or unexpected
zero length OUT data packets.
Stalled Control Transfer
The USB controller automatically issues a STALL handshake to a control transfer under the following
conditions:
1. The Host sends more data during an OUT data phase of a control transfer than was specified
in the Device request during the SETUP phase. This condition is detected by the USB controller
when the Host sends an OUT token (instead of an IN token) after the last OUT packet has been
unloaded and the DATAEND bit in the USB Control and Status Endpoint 0 Low (USBCSRL0)
register has been set.
2. The Host requests more data during an IN data phase of a control transfer than was specified
in the Device request during the SETUP phase. This condition is detected by the USB controller
when the Host sends an IN token (instead of an OUT token) after the CPU has cleared TXRDY
and set DATAEND in response to the ACK issued by the Host to what should have been the last
packet.
3. The Host sends more than USBRXMAXPn bytes of data with an OUT data token.
4. The Host sends more than a zero length data packet for the OUT STATUS phase.
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
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November 17, 2011
Texas Instruments-Production Data