4.5.2. Supported Features
64-Bit SDR Interface to the MAC/RS
Clause 46 of the IEEE 802.3-2008 specification defines the XGMII interface between the XAUI PCS and the Ethernet MAC/RS. The specification requires each of the four XAUI lanes to transfer 8-bit data and 1-bit wide control code at both the positive and negative edge (DDR) of the 156.25 MHz interface clock.
Stratix V transceivers in a XAUI configuration do not support the XGMII interface to the MAC/RS as defined in IEEE 802.3-2008 specification. Instead, they allow the transferring of 16-bit data and 2-bit control code on each of the four XAUI lanes, only at the positive edge (SDR) of the 156.25 MHz interface clock.
Each of the four lanes in a XAUI configuration support an independent 8B/10B encoder/decoder as specified in Clause 48 of the IEEE802.3-2008 specification. 8B/10B encoding limits the maximum number of consecutive 1s and 0s in the serial data stream to five, thereby ensuring DC balance as well as enough transitions for the receiver CDR to maintain a lock to the incoming data.
The XAUI PHY IP core provides status signals to indicate running disparity as well as the 8B/10B code group error.
Transmitter and Receiver State Machines
In a XAUI configuration, the Stratix V transceivers implement the transmitter and receiver state diagrams shown in Figure 48-6 and Figure 48-9 of the IEEE802.3-2008 specification.
In addition to encoding the XGMII data to PCS code groups, in conformance with the 10GBASE-X PCS, the transmitter state diagram performs functions such as converting Idle ||I|| ordered sets into Sync ||K||, Align ||A||, and Skip ||R|| ordered sets.
In addition to decoding the PCS code groups to XGMII data, in conformance with the 10GBASE-X PCS, the receiver state diagram performs functions such as converting Sync ||K||, Align ||A||, and Skip ||R|| ordered sets to Idle ||I|| ordered sets.
The word aligner block in the receiver PCS of each of the four XAUI lanes implements the receiver synchronization state diagram shown in Figure 48-7 of the IEEE802.3-2008 specification.
The XAUI PHY IP core provides a status signal per lane to indicate if the word aligner is synchronized to a valid word boundary.
The lane aligner block in the receiver PCS implements the receiver deskew state diagram shown in Figure 48-8 of the IEEE 802.3-2008 specification.
The lane aligner starts the deskew process only after the word aligner block in each of the four XAUI lanes indicates successful synchronization to a valid word boundary.
The XAUI PHY IP core provides a status signal to indicate successful lane deskew in the receiver PCS.
The rate match FIFO in the receiver PCS datapath compensates up to ±100 ppm difference between the remote transmitter and the local receiver. It does so by inserting and deleting Skip ||R|| columns, depending on the ppm difference.
The clock compensation operation begins after:
- The word aligner in all four XAUI lanes indicates successful synchronization to a valid word boundary.
- The lane aligner indicates a successful lane deskew.
The rate match FIFO provides status signals to indicate the insertion and deletion of the Skip ||R|| column for clock rate compensation.
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