
Philips Semiconductors
PNX15xx Series
Volume 1 of 1
Chapter 23: LAN100 — Ethernet Media Access Controller
PNX15XX_SER_3
Koninklijke Philips Electronics N.V. 2006. All rights reserved.
Product data sheet
Rev. 3 — 17 March 2006
23-4
The Receive Datapath includes:
Receive parser, which detects packet types by parsing part of the packet header
Receive lter, which can lter out certain Ethernet packets, applying different
ltering schemes
Receive buffer, which implements a delay for receive packets to allow the lter to
lter out certain packets before storing them to memory
Receive DMA manager, which reads descriptors from memory and writes data
and status to memory.
2.3 Description
The Ethernet Media Access Controller (LAN100) 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 Standard 802.3
[1]).The MAC sublayer transmits and receives frames to and from 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 MMIO
registers in the LAN100, maintains FIFOs of packets in memory, and receives results
back from the LAN100, typically via interrupts.
When packets are transmitted, packet elds can be concatenated using the
scatter/gather DMA functionality of the LAN100 to avoid unnecessary data copying.
The hardware can add the preamble and start frame delimiter elds, and can
optionally add the CRC under program control. Or, software can partially set up the
Ethernet frames by concatenating the destination address eld, source address eld,
the length/type eld, the MAC client data eld, and optionally, the CRC in the frame
check sequence eld of the Ethernet frame.
When a packet is received, the LAN100 strips the preamble and start frame delimiter
and passes the rest of the packet - the rest is the Ethernet frame - to the device
driver, including destination address, source address, length/type eld, MAC client
data, and frame check sequence.
Apart from its basic packet management functions, the LAN100 contains receive and
transmit DMA managers that control receive- and transmit-data streams. Frames are
passed via descriptor FIFOs (arrays) located in host memory, so that the hardware
can process many packets without software or CPU support. Packets can consist of
multiple fragments that are accessed with scatter/gather DMA. The DMA managers
optimize memory bandwidth by prefetching and buffering.
The LAN100 is connected to the MTL bus using multiple DMA interfaces that perform
data buffering to adapt the data burst rate of the MTL bus to the data rate required for
the Ethernet protocol.
The LAN100 provides MMIO registers via a slave interface to the DCS bus to allow
software to access the internal registers of the LAN100.
Real-time trafc is supported using two transmit queues:
A real-time queue sends frames at the time specied in transmit time-stamps