DP83821 datasheet(21/86 Pages) NSC

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3.0 Functional Description (Continued)

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Table 3-5 Receive

cmdsts Bit Definitions

Excessive Collisions

The number of collisions during the transmission of this

packet was excessive, indicating transmission failure.

If TXCFG register ECRETRY=0, this bit is set after 16

collisions.

If TXCFG register ECRETRY=1, this bit is set after 4

Excessive Collision events (32 collisions).

19-16

CCNT

Collision Count

If TXCFG register ECRETRY=0, this field indicates the

number of collisions encountered during the transmission of

this packet.

If TXCFG register ECRETRY=1,

CCNT[3:2] = Excessive Collisions (0-3)

CCNT[1] = Multiple Collisions

CCNT[0] = Single Collision

Note that Excessive Collisions indicate 16 attempts failed,

while Multiple Collisions and Single Collision indicate

collisions in addition to any excessive collisions. For

example, a collision count of 66 includes 2 Excessive

Collisions and will also set the Single Collision bit.

bit

tag

description

usage

RXA

Receive Aborted

Set to 1 by DP83821 when the receive was aborted. If RXO

is set, then the receive was aborted due to an RX overrun. If

RXO is clear, then a receive descriptor error occurred. SIZE

will be set to the amount of data that was transferred to

memory when the error was detected.

RXO

Receive Overrun

Set to 1 by DP83821 to indicate that a receive overrun

condition occurred. RXA will also be set.

24-23

DEST

Destination Class

When the receive filter is enabled, these bits will indicate the

destination address class as follows:

00 - Packet was rejected

01 - Destination matched the Receive Filter Node Address

10 - Destination is a multicast (but not broadcast)

11 - Destination is a broadcast address

If the Receive Filter is enabled, 00 indicates that the packet

was rejected. Normally packets that are rejected do not

cause any bus activity, nor do they consume receive

descriptors. However, this condition could occur if the packet

is rejected by the Receive Filter later in the packet than the

receive drain threshold (RXCFG:DRTH)

LONG

Too Long Packet

Received

The size of the receive packet exceeded 1518 bytes (1522

bytes if VLAN tag included).

RUNT

Runt Packet Received

The size of the receive packet was smaller than 64 bytes

(including CRC).

ISE

Invalid Symbol Error

(100 Mb only) An invalid symbol was encountered during the

reception of this packet.

CRCE

CRC Error

The CRC appended to the end of this packet was invalid.

FAE

Frame Alignment Error

The packet did not contain an integral number of octets.

LBP

Loopback Packet

The packet is the result of a loopback transmission.

IRL

In-Range Length Error

The receive packet Length/Type field did not match the

length of the data field for the packet. Only valid if the

Length/Type field is a valid length (not a Type value).

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