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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
August 2006
Developer’s Manual
Order Number: 306262--, Revision: 004US
307
USB 1.1 Device Controller—Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network
Processors
8.5.8
UDC Endpoint 6 Control/Status Register
(UDCCS6)
The UDC Endpoint 6 Control Status Register contains six bits that are used to operate
Endpoint 6, a Bulk IN endpoint.
8.5.8.1
Transmit FIFO Service (TFS)
The transmit FIFO service bit is active if one or fewer data packets remain in the
transmit FIFO. TFS is cleared when two complete packets of data remain in the FIFO.
A complete packet of data is signified by loading 64 bytes of data or by setting
UDCCS6[TSP].
8.5.8.2
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 IR6 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 6 Control/Status Register.
The UDCCS6[TPC] bit is cleared by writing a 1 to it. This clears the interrupt source for
the IR6 bit in the appropriate UDC status/interrupt register, but the IR6 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 UDCCS6[TSP].
8.5.8.3
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.
8.5.8.4
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.
UDCCS6[TUR] does not generate an interrupt and is for status only.
UDCCS6[TUR] is cleared by writing a 1 to it.
8.5.8.5
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 UDCCS6[SST] bit is set. To allow the software to continue to send the STALL
condition on the USB bus, the UDCCS6[FST] bit must be set again. The Intel XScale
processor writes a 1 to the sent stall bit to clear it.