High performance Ethernet_(MAC+PHY_) and hands-on section 5

Stellaris Ethernet
1

What is Ethernet?
A communications architecture first implemented in 1974 Ethernet refers to the family of local-area network (LAN) products covered by the IEEE 802.3 standard that defines what is commonly known as the CSMA/CD protocol Five data rates are currently defined for operation over optical fiber and twisted-pair cables:
10Base-T Ethernet (1 Mbps/10 Mbps ) Fast Ethernet (100 Mbps ) Gigabit Ethernet (1000 Mbps ) 10-Gigabit Ethernet (10000 Mbps ) 100-Gigabit Ethernet (100000 Mbps )
2

Ethernet Physical connection
Spec 10BaseT Cable Type Unshielded Twisted Pair Maximum length 100 meters
UTP
10Base2 Thin Coaxial 185 meters
RJ-45
10Base5
Thick Coaxial
500 meters
10BaseF
Fiber Optic
2000 meters
Co-axial
BNC
100BaseT
Unshielded Twisted Pair
100 meters
100BaseTX
Unshielded Twisted Pair
220 meters
Fiber-optic
3

Stellaris? Ethernet Hardware design
4

Media Access Control (MAC)
Flow Control MII Management Transmitter Buffers Receiver Buffers
Medium Independent Interface (MII)
5

Ethernet PHY
Medium Independent Interface (MII)
10BaseT
Lookback support Transmitter Receiver PLL Manchester Encoding
100BaseTX
Transmitter Receiver 4B/5B encoding
6

Media Independent Interface
MEDIA INDEPENDENT INTERFACE DESCRIPTION
The Media Independent Interface is a standard to facilitate the transfer of data between the MAC and the physical layer interface. The MII interface is a four bit (nibble) wide data path interface that runs at 25 MHz for a 100 Mbps networks and at 2.5 MHz for 10 Mbps networks. The MII receive clock is generated by the PHY and is sent to the MAC on the RX_CLK pin. The data from the PHY on RXD[3:0] is presented synchronous to the rising edge of RX_CLK. The receive process is started when RX_DV is asserted and remains asserted for the entire receive frame length.1
7

Networking – The Layer Model
?
Networks are structured in layers
?
Aim is to abstract specifics of the underlying layer(s)
? ? ?
E.g. Web broswer doesn’t care if you use Ethernet or WLAN Each layer can communicate with the same layer on a different host Note that only the PHY layer is physically connected
?
The collection of layers is also called ”Network Stack”
8

TCP/IP protocol stack
Application Layer: DHCP, DNS, FTP, HTTP, IMAP4, IRC, NNTP, XMPP, POP3, RTP, SIP, SMTP,
SNMP, SSH, TELNET, RPC, RTCP, RTSP, TLS (and SSL), SDP, SOAP, GTP, STUN, NTP, etc...
Transport Layer: TCP, UDP, DCCP, SCTP, RSVP, ECN, etc... Network/Internet Layer: IP (IPv4, IPv6), OSPF, IS-IS, BGP, IPsec, ARP, RARP, RIP, ICMP, ICMPv6,
IGMP, etc...
Data Link Layer: Ethernet, 802.11 (WLAN), 802.16, Wi-Fi, WiMAX, ATM, DTM, Token ring, FDDI,
Frame Relay, GPRS, EVDO, HSPA, HDLC, PPP, PPTP, L2TP, ISDN, ARCnet, LLTD, etc...
Physical Layer: Ethernet physical layer, Twisted pair, Modems, PLC, SONET/SDH, G.709, Optical
fiber, Coaxial cable, etc...
Application Layer Transport Layer Network Layer Link Layer Physical Layer
FTP
TELNET
RLOGIN
SMTP
DNS
HTTP
TFTP
…
TCP IP Ethernet/ATM/Wireless Twisted pair
UDP ICMP ARP Optical fiber IGMP
… … … …
9

Link Layer
?
Link Layer establishes point to point connections
? ? ?
Data is send from one Ethernet MAC to another Data exchange via standardized Ethernet frames Ethernet frame specifies:
?
Preamble
?
Used to synchronize transmitter and receiver
? ? ?
Source MAC adress (6-Byte) Destination MAC adress (6-Byte) Type of packet sent (2-Byte)
?
Used to determine which protocol will handle the received data
? ?
Data (minimum 46-Byte, maximum 1500-Byte) Checksum (4Byte)
10

Link Layer in Stellaris
?
Stellaris implements all link layer functions
?
RX and TX FIFO
?
2kByte each – exceeding the 1500Byte standard
?
Configurable MAC adress
? ?
Pre-generated adress exist in User0 and User1 registers Automatic MAC filtering
? ? ?
Accept only frames to the own MAC address or the broadcast address (all 0xFF) Option to switch to promiscuous mode (accept all frames) Option to enable multi-cast
?
Automatic padding option
?
Add zeros to frames shorter than 40 Byte
?
Automatic CRC generation and check
?
Frames with CRC error can be automatically discarded
11

Network Layer
?
Network layer establishes end to end communication
? ? ?
Data can travel via intermediary hosts Data protocols are embedded into standard Ethernet frames Two main protocols are relevant at the network layer
?
IP and ICMP
?
?
IP = Internet protocol ? Basic data exchange protocol ICMP – Internet Control Message Protocol ? Uses IP format for tasks such as ping, time request, error reporting etc. ARP = Adress Resolution Protocol Translates 32-Bit IP adresses into 48-Bit MAC Addresses Used to determine the MAC adress of the IP receiver
?
ARP
? ? ?
?
Ethernet Packet Type determines which protocol handles received data
? ?
0x0800 0x0806
Packet is intended for IP Packet is intended for ARP
12

Transport Layer
?
Transport layer establishes reliable host to host communication
? ? ?
Main task is to control reliability of the connection Can also provide tunnelling services (IPsec) Two main protocols are relevant at the transport layer
?
Transmission Control Protocol (TCP)
? ?
Provides reliable and ordered exchange of data Used by most internet protocols such as HTTP, FTP, SIP Simple transmission, unreliable Ideal for answering many small requests and to transfer data fast Used by DNS and VoIP
?
User Datagram Protocol (UDP)
? ? ?
?
Protocol field in the IP header determines which protocol handles received data
? ?
0x06 0x11
Packet is intended for TCP Packet is intended for UDP
13

Application Layer
?
Application Layer uses the data transmitted
? ?
Web browser, FTP program, VoIP program ... Destination application is determined via the port number in TCP / UDP
?
Set of defined port numbers exists
? ? ?
Port 20 = FTP Port 80 = HTTP Port 389 = LDAP
14

Hypertext Transfer Protocol Example
HTTP
request/response
HTTP
User agent
Origin Server stores or creates resources such as HTML files and images
TCP
Port 80
TCP
IP
Client
Ethernet MAC
IP
Ethernet MAC
Ethernet PHY
Ethernet PHY
Server
15

Communications Stacks for Stellaris?
Micriμm μC/TCP-IP Express Logic NetX? TCP/IP protocol stack CMX-MicroNet? protocol stacks
InterNiche TCP/IP NicheStack?, NicheLITE?, and add-on modules such as HTTP, SNMP, and security protocols EtherNet/IP? protocol stacks
https://www.360docs.net/doc/294538514.html, Open-Source μIP Embedded web server
μIP lwIP
Open source TCP/IP stack for small footprint embedded systems Open source light-weight implementation of the TCP/IP stack for small RAM
embedded systems IEEE 1588 PTP (Precision Time Protocol)
16

Communications Stacks for Stellaris?
?
List is subject to change
17

Ethernet Extras: IEEE 1588? System
An IEEE 1588 system is a collection of IEEE 1588 Clocks configured in such a way that all of the clocks synchronize with each other to maintain a consistent timescale. IEEE 1588 allows the clocks in the system components to synchronize to a high degree of accuracy. Microsecond accuracy is easily achievable using low cost, small footprint implementations such as Stellaris. How are the synchronized clocks used? The clocks in an IEEE 1588 system are typically used to coordinate the activities of the primary applications executing on the system. For example, sensor data may be time stamped at the source. Since all clocks are synchronized, the time stamped data may be correlated in post acquisition operations. The clocks may also be used in initiating actions in one or more components based on the times of the local clocks. For example an actuator could be commanded to change its value at time T and a sensor to measure a value at time T+delta. Since the clocks are synchronized, the resulting actions are coordinated in time.
18

Ethernet Extras: IEEE 1588?
Before IEEE 1588, Ethernet communication in control applications occurred without absolute determinism:
Assume Sender sends a control instruction Turn to Controller Assume also that Clock S and Clock C are not synchronized
If Sender asks Controller
to Turn upon receipt of the instruction, then
there is no telling when Controller will receive Turn.
“TURN!”
Sender Clock S
(some ?? time later) “Ok!”
Controller Clock C
Uh-oh! Ethernet is non-deterministic by nature.
Even if Sender asks Controller to Turn at a given time alpha, there is still the problem of unsynchronized clocks.
Sender Clock S
“TURN at alpha!”
“Ok! I will TURN at alpha.”
Controller Clock C
Uh-oh! Alpha on Clock S ≠ Alpha on Clock C.
But if Sender asks Controller to Turn at a given time alpha, and the clocks are synchronized to a master, then determinism is achieved.
Sender Clock S
“TURN at alpha!”
“Ok! I will TURN at alpha.”
Controller Clock C
Yes! Alpha on Clock S = Alpha on Clock C.
19

Ethernet Extras: PTP in Industrial Applications
Industry synchronization requirements for PTPA
PTP and motion control
Variable frequency drives require few 10s of microseconds
Software generally 5uS 44% of applications are networked, 63% use Ethernet TCP/IPB
Servo-controlled systems require 100s of nanoseconds
Requires significant hardware assist 36% of applications are networked, 56% use Ethernet TCP/IPC
Stellaris implementation
Open source lwIP + PTPd : within 500nS of master clock, jitter +/- 500nS This represents a greater than ten fold improvement over typical SW-only implementations.
A
2002, https://www.360docs.net/doc/294538514.html,/PTTI_draft_final.pdf https://www.360docs.net/doc/294538514.html,/article/CA315281.html C 2004, https://www.360docs.net/doc/294538514.html,/article/CA407419.html?text=1588
B 2003,
20