LM3S5C36 Datasheet, PDF (803/1068 Pages) Texas Instruments – Stellaris® LM3S5C36 Microcontroller

Stellaris^® LM3S5C36 Microcontroller
controller first clears the FULL bit, then sets RXRDY again to indicate that there is another packet
waiting in the FIFO to be unloaded.
Note: Double-packet buffering is disabled if an endpoint’s corresponding EPn bit is set in the USB
Receive Double Packet Buffer Disable (USBRXDPKTBUFDIS) register. This bit is set
by default, so it must be cleared to enable double-packet buffering.
17.3.1.4
Scheduling
The Device has no control over the scheduling of transactions as scheduling is determined by the
Host controller. The Stellaris USB controller can set up a transaction at any time. The USB controller
waits for the request from the Host controller and generates an interrupt when the transaction is
complete or if it was terminated due to some error. If the Host controller makes a request and the
Device controller is not ready, the USB controller sends a busy response (NAK) to all requests until
it is ready.
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.
January 23, 2012
803
Texas Instruments-Production Data