82801DB Datasheet, PDF (175/587 Pages) Intel Corporation – Intel 82801DB I/O Controller Hub 4 (ICH4)

Functional Description
Table 5-58. TD Control and Status (Sheet 2 of 2)
Bit
Description
22
21
20
19
18
17
16
15:11
10:0
Stalled.
1 = Set to a 1 by the ICH4 during status updates to indicate that a serious error has occurred at the
device/endpoint addressed by this TD. This can be caused by babble, the error counter
counting down to zero, or reception of the STALL handshake from the device during the
transaction. Any time that a transaction results in the Stalled bit being set, the Active bit is also
cleared (set to 0). If a STALL handshake is received from a SETUP transaction, a Time Out
Error will also be reported.
Data Buffer Error (DBE).
1 = Set to a 1 by the ICH4 during status update to indicate that the ICH4 is unable to keep up with
the reception of incoming data (overrun) or is unable to supply data fast enough during
transmission (underrun). When this occurs, the actual length and Max Length field of the TD
will not match. In the case of an underrun, the ICH4 will transmit an incorrect CRC (thus
invalidating the data at the endpoint) and leave the TD active (unless error count reached zero).
If a overrun condition occurs, the ICH4 will force a timeout condition on the USB, invalidating
the transaction at the source.
Babble Detected (BABD).
1 = Set to a 1 by the ICH4 during status update when “babble” is detected during the transaction
generated by this descriptor. Babble is unexpected bus activity for more than a preset amount
of time. In addition to setting this bit, the ICH4 also sets the” STALLED” bit (bit 22) to a 1. Since
“babble” is considered a fatal error for that transfer, setting the” STALLED” bit to a 1 insures that
no more transactions occur as a result of this descriptor. Detection of babble causes immediate
termination of the current frame. No further TDs in the frame are executed. Execution resumes
with the next frame list index.
Negative Acknowledgment (NAK) Received (NAKR).
1 = Set to a 1 by the ICH4 during status update when the ICH4 receives a “NAK” packet during the
transaction generated by this descriptor. If a NAK handshake is received from a SETUP
transaction, a Time Out Error will also be reported.
CRC/Time Out Error (CRC_TOUT).
1 = Set to a 1 by the ICH4 as follows:
• During a status update in the case that no response is received from the target device/endpoint
within the time specified by the protocol chapter of the USB specification.
• During a status update when a Cycli Redundancy Check (CRC) error is detected during the
transaction associated with this transfer descriptor.
In the transmit case (OUT or SETUP Command), this is in response to the ICH4 detecting a timeout
from the target device/endpoint.
In the receive case (IN Command), this is in response to the ICH4’s CRC checker circuitry detecting
an error on the data received from the device/endpoint or a NAK or STALL handshake being
received in response to a SETUP transaction.
Bit stuff Error (BSE).
1 = This bit is set to a 1 by the ICH4 during status update to indicate that the receive data stream
contained a sequence of more than 6 ones in a row.
Bus Turn Around Time-out (BTTO).
1 = This bit is set to a 1 by the ICH4 during status updates to indicate that a bus time-out condition
was detected for this USB transaction. This time-out is specially defined as not detecting an
IDLE-to ‘K’ state Start of Packet (SOP) transition from 16 to 18-bit times after the SE0-to-IDE
transition of previous End of Packet (EOP).
Reserved
Actual Length (ACTLEN). The Actual Length field is written by the ICH4 at the conclusion of a USB
transaction to indicate the actual number of bytes that were transferred. It can be used by the
software to maintain data integrity. The value programmed in this register is encoded as n-1 (see
Maximum Length field description in the TD Token).
Intel^® 82801DB ICH4 Datasheet
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