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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
116 of 808
NXP Semiconductors
UM10360
Chapter 10: LPC17xx Ethernet
The Ethernet frame consists of the destination address, the source address, an optional
VLAN field, the length/type field, the payload and the frame check sequence.
Each address consists of 6 bytes where each byte consists of 8 bits. Bits are transferred
starting with the least significant bit.
8.
Overview
8.1 Partitioning
The Ethernet block and associated device driver software offer the functionality of the
Media Access Control (MAC) sublayer of the data link layer in the OSI reference model
(see IEEE std 802.3). The MAC sublayer offers the service of transmitting and receiving
frames to the next higher protocol level, the MAC client layer, typically the Logical Link
Control sublayer. The device driver software implements the interface to the MAC client
layer. It sets up registers in the Ethernet block, maintains descriptor arrays pointing to
frames in memory and receives results back from the Ethernet block through interrupts.
When a frame is transmitted, the software partially sets up the Ethernet frames by
providing pointers to the destination address field, source address field, the length/type
field, the MAC client data field and optionally the CRC in the frame check sequence field.
Preferably concatenation of frame fields should be done by using the scatter/gather
functionality of the Ethernet core to avoid unnecessary copying of data. The hardware
adds the preamble and start frame delimiter fields and can optionally add the CRC, if
requested by software. When a packet is received the hardware strips the preamble and
start frame delimiter and passes the rest of the packet - the Ethernet frame - to the device
driver, including destination address, source address, length/type field, MAC client data
and frame check sequence (FCS).
Apart from the MAC, the Ethernet block contains receive and transmit DMA managers that
control receive and transmit data streams between the MAC and the AHB interface.
Frames are passed via descriptor arrays located in host memory, so that the hardware
can process many frames without software/CPU support. Frames can consist of multiple
fragments that are accessed with scatter/gather DMA. The DMA managers optimize
memory bandwidth using prefetching and buffering.
A receive filter block is used to identify received frames that are not addressed to this
Ethernet station, so that they can be discarded. The Rx filters include a perfect address
filter and a hash filter.
Wake-on-LAN power management support makes it possible to wake the system up from
a power-down state -a state in which some of the clocks are switched off -when wake-up
frames are received over the LAN. Wake-up frames are recognized by the receive filtering
modules or by a Magic Frame detection technology. System wake-up occurs by triggering
an interrupt.
An interrupt logic block raises and masks interrupts and keeps track of the cause of
interrupts. The interrupt block sends an interrupt request signal to the host system.
Interrupts can be enabled, cleared and set by software.