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UM10237_2

© NXP B.V. 2008. All rights reserved.

 

For multi-fragment frames, the value of the LateCollision, ExcessiveCollision, 
ExcessiveDefer, Defer and CollissionCount bits in all but the last fragment in the frame will 
be 0. The status of the last fragment in the frame will copy the value for these bits from the 
MAC. All fragment statuses will have valid Error, NoDescriptor and Underrun bits.

This section defines the functions of the DMA capable 10/100 Ethernet MAC. After 
introducing the DMA concepts of the Ethernet block, and a description of the basic 
transmit and receive functions, this section elaborates on advanced features such as flow 
control, receive filtering, etc.

The Ethernet block can transmit and receive Ethernet packets from an off-chip Ethernet 
PHY connected through the MII or RMII interface. MII or RMII mode can be selected from 
software.

Typically during system start-up, the Ethernet block will be initialized. Software 
initialization of the Ethernet block should include initialization of the descriptor and status 
arrays as well as the receiver fragment buffers.

To transmit a packet the software driver has to set up the appropriate Control registers 
and a descriptor to point to the packet data buffer before transferring the packet to 
hardware by incrementing the TxProduceIndex register. After transmission, hardware will 
increment TxConsumeIndex and optionally generate an interrupt.

The hardware will receive packets from the PHY and apply filtering as configured by the 
software driver. While receiving a packet the hardware will read a descriptor from memory 
to find the location of the associated receiver data buffer. Receive data is written in the 

20:0

-

Unused

24:21 CollisionCount

The number of collisions this packet incurred, up to the 
Retransmission Maximum.

25

Defer

This packet incurred deferral, because the medium was occupied. 
This is not an error unless excessive deferral occurs.

26

ExcessiveDefer

This packet incurred deferral beyond the maximum deferral limit and 
was aborted.

27

ExcessiveCollision Indicates this packet exceeded the maximum collision limit and was 

aborted.

28

LateCollision

An Out of window Collision was seen, causing packet abort.

29

Underrun

A Tx underrun occurred due to the adapter not producing transmit 
data.

30

NoDescriptor

The transmit stream was interrupted because a descriptor was not 
available.

31

Error

An error occurred during transmission. This is a logical OR of 
Underrun, LateCollision, ExcessiveCollision, and ExcessiveDefer.