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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
August 2006
Developer’s Manual
Order Number: 306262--, Revision: 004US
299
USB 1.1 Device Controller—Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network
Processors
8.5.4.5
Sent Stall (SST)
The sent stall bit is set by the UDC in response to FST successfully forcing a user-
induced STALL on the USB bus. This bit is not set if the UDC detects a protocol violation
from the host PC when a STALL handshake is returned automatically. In either event,
the Intel XScale processor does not intervene and the UDC clears the STALL status
when the host sends a CLEAR_FEATURE command.
Any valid data in the FIFO remains valid and the software must unload it. The endpoint
operation continues normally and does not send another STALL condition, even if the
UDCCS2[SST] bit is set. To allow the software to continue to send the STALL condition
on the USB bus, the UDCCS2[FST] bit must be set again.
The Intel XScale processor writes a 1 to the sent stall bit to clear it.
8.5.4.6
Force Stall (FST)
The Intel XScale processor can set the force stall bit to force the UDC to issue a STALL
handshake to all OUT tokens. STALL handshakes continue to be sent until the Intel
XScale processor clears this bit by sending a Clear Feature command.
The UDCCS2[SST] bit is set when the STALL state is actually entered, but this may be
delayed if the UDC is active when the UDCCS2[FST] bit is set. The UDCCS2[FST] bit is
automatically cleared when the UDCCS2[SST] bit is set.
To ensure that no data is transmitted after the Clear Feature command is sent and the
host resumes IN requests, software must clear the transmit FIFO by setting the
UDCCS2[FTF] bit.
8.5.4.7
Receive FIFO Not Empty (RNE)
The receive FIFO not empty bit indicates that unread data remains in the receive FIFO.
This bit must be polled when the UDCCS2[RPC] bit is set to determine if there is any
data in the FIFO that the Intel XScale processor did not read. The receive FIFO must
continue to be read until this bit clears or data will be lost.
8.5.4.8
Receive Short Packet (RSP)
The UDC uses the receive short packet bit to indicate that the received OUT packet in
the active buffer currently being read is a short packet or zero-sized packet. This bit is
updated by the UDC after the last byte is read from the active buffer and reflects the
status of the new active buffer.
If UDCCS2[RSP] is a 1 and UDCCS2[RNE] is a 0, it indicates a zero-length packet. If a
zero-length packet is present, the Intel XScale processor must not read the data
register. UDCCS2[RSP] is cleared when the next OUT packet is received.