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Intel
®
IXP42X product line and IXC1100 control plane processors—Universal Serial Bus (USB)
v1.1 Device Controller
Intel
®
IXP42X Product Line of Network Processors and IXC1100 Control Plane Processor
DM September 2006
486 Order Number: 252480-006US
18.5.3.2 Transmit Packet Complete (TPC)
The transmit packet complete bit is set by the UDC when an entire packet is sent to the
host. When this bit is set, the IR1 bit in the appropriate UDC status/interrupt register is
set if transmit interrupts are enabled. This bit can be used to validate the other status/
error bits in the endpoint 1control/status register.
The UDCCS1[TPC] bit is cleared by writing a 1 to it. This clears the interrupt source for
the IR1 bit in the appropriate UDC status/interrupt register, but the IR1 bit must also
be cleared.
Setting this bit does not prevent the UDC from transmitting the next buffer. The UDC
issues NAK handshakes to all IN tokens if this bit is set and neither buffer has been
triggered by writing 64 bytes or setting UDCCS1[TSP].
18.5.3.3 Flush Tx FIFO (FTF)
The Flush Tx FIFO bit triggers a reset for the endpoint's transmit FIFO. The Flush Tx
FIFO bit is set when software writes a 1 to it or when the host performs a
SET_CONFIGURATION or SET_INTERFACE.
The bit’s read value is 0.
18.5.3.4 Transmit Underrun (TUR)
The transmit underrun bit is set if the transmit FIFO experiences an underrun. When
the UDC experiences an underrun, NAK handshakes are sent to the host.
UDCCS1[TUR] does not generate an interrupt and is for status only. UDCCS1[TUR] is
cleared by writing a 1 to it.
18.5.3.5 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. The endpoint operation continues
normally and does not send another STALL condition, even if the UDCCS1[SST] bit is
set.
To allow the software to continue to send the STALL condition on the USB bus, the
UDCCS1[FST] bit must be set again. The Intel XScale
®
processor writes a 1 to the sent
stall bit to clear it.
18.5.3.6 Force STALL (FST)
The Intel XScale
®
processor can set the force stall bit to force the UDC to issue a STALL
handshake to all IN tokens. STALL handshakes continue to be sent until the Intel
XScale
®
processor clears this bit by sending a Clear Feature command.
The UDCCS1[SST] bit is set when the STALL state is actually entered, but this may be
delayed if the UDC is active when the UDCCS1[FST] bit is set. The UDCCS1[FST] bit is
automatically cleared when the UDCCS1[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
UDCCS1[FTF] bit.