UM10360 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
User manual Rev. 3 — 19 December 2013 178 of 841
NXP Semiconductors
UM10360
Chapter 10: LPC176x/5x Ethernet
The transmit status consists of one word which is the StatusInfo word. It contains flags
returned by the MAC and flags generated by the transmit data path reflecting the status of
the transmission. Table 183
lists the bit definitions in the StatusInfo word.
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.
10.16 Ethernet block functional description
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.
10.16.1 Overview
The Ethernet block can transmit and receive Ethernet packets from an off-chip Ethernet
PHY connected through the RMII interface.
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.
Remark: When initializing the Ethernet block, it is important to first configure the PHY and
ensure that reference clocks (ENET_REF_CLK signal in RMII mode, or both
ENET_RX_CLK and ENET_TX_CLK signals in MII mode) are present at the external pins
and connected to the EMAC module (selecting the appropriate pins using the PINSEL
registers) prior to continuing with Ethernet configuration. Otherwise the CPU can become
locked and no further functionality will be possible. This will cause JTAG lose
communication with the target, if debug mode is being used.
Table 183. Transmit status information word
Bit Symbol Description
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.
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