Ethernet on the FPGA

1
Ethernet on the FPGA
2
About Ethernet

• Standard for interconnecting local area networks
• Many standards we focus on IEEE 802.3
• Copper twisted pair wires
• 10BASET and 100BASE-T
• This lab uses 10BASE-T

3
OSI Model

• Above layer 4, gets fuzzy

4
Physical layer - Ethernet

• Twisted pair cable
• Differential signaling
• 10 megabits / second
• Manchester encoding (for 10BASE-T)

5
Link Layer Ethernet

• Thankfully hardware on the FPGA takes care of
  converting those signals into data for us
• From the FPGA, we see digital data (similar to
  what comes out of async_receiver, but a nibble at
  a time)

Inside FPGA
TX clk
MAC
PHY
TX data 30
Ethernet plug
RX data 30
RX clk
6
Link Layer Ethernet

• Still have to decode it tho. So what does an
  Ethernet frame look like?
• This is the gory details we have to do in the
  FPGA
• (Translating the nibbles of data into a sense)

7
Network and Transport layer orhow do I do
something useful?

• To interoperate with normal machines, youve got
  to use TCP/IP stack
• IP header is pretty simple actually

8
Network and Transport layer orhow do I do
something useful?

• To actually send the data, well use UDP because
  its simplest. Very little extra fluff

9
Putting it all together an example

• Lets use UDP to control an LED on the FPGA using
  our PC
• Well send a UDP packet with information
  containing the values of the LEDs

10
Simple example

• To keep it simple, well broadcast the data by
  sending it to every device on the network. This
  is done by using the special ip address
  x.x.x.255.
• Well send the status LED values as a single byte
  of data in our UDP packet.
• Well use Python to send the data from a Windows
  computer

11
Python program
12
Ethernet frame

• This causes Windows to send the following
  Ethernet packet out on the wire

13
Decode on the FPGA

• Which we can then decode on the FPGA with a state
  machine