Saturday, December 18, 2010

Introduction to MAC

Medium Access Control  (MAC) is connected to PHY via Media Independent Interface (MII)  toward network side. MII could be GMII, XGMII, XLGMII or CGMII, and it depends on the speed --- 1GbE, 10GbE, 40GbE or 100GbE. On the other end, MAC is connected to host via TX FIFO or RX FIFO.   In most implementation,  MAC consists of Reconciliation Sublayer, RX control, TX control,  Receive FIFO, TX FIFO, Time stamping,  Configuration and Statistics registers, and MDIO master.  The RS is responsible for spraying packets onto the interface defined by MII and local/remote fault stuff.
The functionality of one general MAC is listed as following:
  1. Transit or receive Ethernet frames from PHY, detect or insert preamble and SFD,  verify or calculate CRC-32 or FCS, terminate or insert optional padding,  terminate pause or generate Xon / Xoff pause, extract or add IEEE1588 time stamp
  2. Support configuring MAC address, frame length,  half/full duplex, promiscuous mode
  3. Support IEEE 802.1Q VLAN
  4. Support statistics compatible with SNMP or RMON 
  5. Support MDIO master to access PHY 

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