Ethernet

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Ethernet

• Ethernet Controller
• How do you interface with an Ethernet PHY?

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Ethernet Controller Block Diagram
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Ethernet MAC-PHY Media-Independent Interface (MII)
MDIO
NetARM MAC
PHY
PHY Mgt (e.g., setup)
MDCLK
TXD
Tx Data
TXEN
Data Ready
RXDV
TXER
Tx/Rx Error
RXER
TXCLK
Clocks for Tx/Rx
RXCLK
Rx Data
RXD
CRS
Carrier Sense
Collision
COL
(Remainder of MII pins are V or GND.)
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PHY Management

• Software sends/receives a serial stream on MDIO,
  clocked by MDCLK.
• Stream consists of management frames, each
  causing a PHY register to be read or written.
• Registers 0 1 predefined, required
• Registers 2 7 predefined, optional
• Registers 8 15 reserved
• Registers 16 31 vendor-specific

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Culture Management Frame Format
Preamble FS OP PHY Addr Reg Addr TA DATA
READ 32 1s 01 10 xxxxx xxxxx 00 xxxxxxxxxxxxxxxx
WRITE 32 1s 01 01 xxxxx xxxxx 00 xxxxxxxxxxxxxxxx

• Preamble 32 consecutive 1s
• FS start of frame
• OP read or write
• PHY Address 0 to 31 usually specified via PHY
  pins
• Register Address 0 to 31
• TA Turnaround separator between frame header
  and data
• Data 16 bits
• Ends with high-impedance idle state

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MII PHY Predefined Registers

• 0 Control
• 1 Status
• 2, 3 PHY ID (manufacturer, model, rev
  optional)
• 4 Auto Negotiation Advertisement (optional)
• 5 Auto Negotiation Link Partner (optional)
• 6 Auto Negotiation Expansion (optional)
• 7 Auto Negotiation Next Page Xmit (optional)
• Consult your PHY documentation for register usage

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Managing the PHY through MII
Preamble FS OP PHY Addr Reg Addr TA DATA
READ 32 1s 01 10 xxxxx xxxxx 00 xxxxxxxxxxxxxxxx
WRITE 32 1s 01 01 xxxxx xxxxx 00 xxxxxxxxxxxxxxxx
From MII Address Register (0xFF800544)
From MII Write Data Register (0xFF800548)
Initiate by MII Command Register (0xFF800540)
To MII Read Data Register (0xFF80054C)

• Writes are initiated by writing to MWTD.
• Read/write done when BUSY in MII Indicators
  Register (0xFF800550) returns to 0.

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Auto-Negotiation

• Exchange configuration information between two
  ends of a link segment and automatically select
  the highest common performance mode .
• When
• Power up
• Reset (hardware and software)
• Link failure and comes back up
• Software re-start
•  
•  
•  

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Parallel Detection

• When partner does not support Auto-Negotiation
• Automatically detect the presence of either link
  pulse (10 Mbps) or idle symbol (100 Mbps) and set
  speed accordingly.
• Set Half mode.