DP83936AVF datasheet(23/104 Pages) NSC

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40 TransmitReceive IEEE 8023 Frame Format (Continued)

ets from reaching a node There are three types of address

formats supported by the SONIC-T Physical Multicast and

Broadcast

Physical Address

The physical address is a unique ad-

dress that corresponds only to a single node All physical

addresses have the LSB of the first byte of the address set

to ‘‘0’’ These addresses are compared to the internally

stored CAM (Content Addressable Memory) address en-

tries All bits in the destination address must match an entry

in the CAM in order for the SONIC-T to accept the packet

Multicast Address

Multicast addresses which have the

LSB of the first byte of the address set to ‘‘1’’ are treated

similarly as physical addresses ie

they must match an

entry in the CAM This allows perfect filtering of Multicast

packets and eliminates the need for a hashing algorithm for

mapping Multicast packets

Broadcast Address

If the address consists of all 1’s it is a

Broadcast address indicating that the packet is intended for

all nodes

The SONIC-T also provides a promiscuous mode which al-

lows reception of all physical address packets Physical

Multicast Broadcast and promiscuous address modes can

be selected via the Receive Control register

43 SOURCE ADDRESS

The source address is the physical address of the sending

node Source addresses cannot be multicast or broadcast

addresses This field must be passed to the SONIC-T’s

transmit buffer from the system software During transmis-

sion the SONIC-T compares the Source address with its

internal CAM address entries before monitoring the CRC of

the self-received packet If the source address of the packet

transmitted does not match a value in the CAM the packet

monitored bad flag (PMB) will be set in the transmit status

field of the transmit descriptor (see Sections 5512 and

644) The SONIC-T does not provide Source Address in-

sertion However a transmit descriptor fragment containing

only the Source Address may be created for each packet

(See Section 551)

44 LENGTHTYPE FIELD

For IEEE 8023 type packets this field indicates the number

of bytes that are contained in the data field of the packet

For Ethernet I and II networks this field indicates the type of

packet The SONIC-T does not operate on this field

45 DATA FIELD

The data field has a variable octet length ranging from 46 to

1500 bytes as defined by the Ethernet specification Mes-

sages longer than 1500 bytes need to be broken into multi-

ple packets for IEEE 8023 networks Data fields shorter

than 46 bytes require appending a pad to bring the com-

plete frame length to 64 bytes If the data field is padded

the number of valid bytes are indicated in the length field

The SONIC-T does not append pad bytes for short packets

during transmission nor check for oversize packets during

reception However the user’s driver software can easily

append the pad by lengthening the TXpktpkt

size field

and TXpktfrag

size field(s) to at least 64 bytes (see Sec-

tion 551) Although the Ethernet specification defines the

maximum number of bytes in the data field the SONIC-T

can transmit and receive packets up to 64k bytes

46 FCS FIELD

The Frame Check Sequence (FCS) is a 32-bit CRC field

calculated and appended to a packet during transmission to

allow detection of error-free packets During reception an

error-free packet results in a specific pattern in the CRC

generator The AUTODIN II (X32 a X26 a X23 a X22 a

X16 a X12 a X11 a X10 a X8 a X7 a X5 a X4 a

X2 a X1 a 1) polynomial is used for the CRC calculations

The SONIC-T may optionally append the CRC sequence

during transmission and checks the CRC both during nor-

mal reception and self-reception during a transmission (see

Section 331)

47 MAC (MEDIA ACCESS CONTROL) CONFORMANCE

The SONIC-T is designed to be compliant to the IEEE 8023

MAC Conformance specification The SONIC-T implements

most MAC functions in silicon and provides hooks for the

user software to handle the remaining functions The MAC

Conformance specifications are summarized in Table 4-1

TABLE 4-1 MAC Conformance Specifications

Conformance

Test Name

Support By

SONIC-T

User Driver

Notes

Software

Minimum Frame Size

Maximum Frame Size

Address Generation

Address Recognition

Pad Length Generation

Start Of Frame Delimiter

Length Field

Preamble Generation

Order of Bit Transmission

Inconsistent Frame Length

Non-Integral Octet Count

Incorrect Frame Check

Sequence

Frame Assembly

FCS Generation and Insertion

Carrier Deference

Interframe Spacing

Collision Detection

Collision Handling

Collision Backoff and

Retransmission

FCS Validation

Frame Disassembly

Back-to-Back Frames

Flow Control

Attempt Limit

Jam Size (after SFD)

Jam Size (in Preamble)

Note 1

The SONIC-T provides the byte count of the entire packet in the

RXpktbyte

count (see Section 543) The user’s driver software may per-

form further filtering of the packet based upon the byte count

Note 2

The SONIC-T does not provide Source Address insertion however

a transmit descriptor fragment containing only the Source Address may be

created for each packet (See Section 551)

Note 3

The SONIC-T does not provide Pad generation however the user’s

driver software can easily append the Pad by lengthening the TXpktpkt

size field and TXpktfrag

size field(s) to at least 64 bytes (See Section

551)

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