FW82801DB S L66K Intel, FW82801DB S L66K Datasheet - Page 187

• Manufacturer Part Number: FW82801DB S L66K
• Manufacturer: Intel

Specifications of FW82801DB S L66K

• Lead Free Status / RoHS Status: Supplier Unconfirmed

5.16.4.7
5.16.5
5.16.5.1
5.16.5.2
Intel
®
Table 5-71. Token Format
82801DB ICH4 Datasheet
Cyclic Redundancy Check (CRC)
CRC is used to protect the all non-PID fields in token and data packets. In this context, these fields
are considered to be protected fields. The PID is not included in the CRC check of a packet
containing CRC. All CRCs are generated over their respective fields in the transmitter before bit
stuffing is performed. Similarly, CRCs are decoded in the receiver after stuffed bits have been
removed. Token and data packet CRCs provide 100% coverage for all single and double bit errors.
A failed CRC is considered to indicate that one or more of the protected fields is corrupted and
causes the receiver to ignore those fields, and, in most cases, the entire packet.
Packet Formats
Token Packets
Table 5-71
IN, OUT, or SETUP packet type, and ADDR and ENDP fields. For OUT and SETUP transactions,
the address and endpoint fields uniquely identify the endpoint that will receive the subsequent data
packet. For IN transactions, these fields uniquely identify which endpoint should transmit a data
packet. Only the ICH4 can issue token packets. IN PIDs define a data transaction from a function
to the ICH4. OUT and SETUP PIDs define data transactions from the ICH4 to a function.
Token packets have a five-bit CRC that covers the address and endpoint fields as shown above. The
CRC does not cover the PID, which has its own check field. Token and SOF packets are delimited
by an EOP after three bytes of packet field data. If a packet decodes as an otherwise valid token or
SOF but does not terminate with an EOP after three bytes, it must be considered invalid and
ignored by the receiver.
Start of Frame Packets
Table 5-72
rate of once every 1.00 ms 0.05. SOF packets consist of a PID indicating packet type followed by
an 11-bit frame number field.
The SOF token comprises the token-only transaction that distributes a start of frame marker and
accompanying frame number at precisely timed intervals corresponding to the start of each frame.
All full speed functions, including hubs, must receive and decode the SOF packet. The SOF token
does not cause any receiving function to generate a return packet; therefore, SOF delivery to any
given function cannot be guaranteed. The SOF packet delivers two pieces of timing information. A
function is informed that a start of frame has occurred when it detects the SOF PID. Frame timing
sensitive functions, which do not need to keep track of frame number, need only decode the SOF
PID; they can ignore the frame number and its CRC. If a function needs to track frame number, it
must comprehend both the PID and the time stamp.
Packet
ADDR
ENDP
CRC5
PID
shows the field formats for a token packet. A token consists of a PID, specifying either
shows a start of frame (SOF) packet. SOF packets are issued by the host at a nominal
Width
8 bits
7 bits
4 bits
5 bits
Functional Description
187