Xilinx 1000BASE-X - Manual (Page 158)

158 www.xilinx.com Ethernet 1000BASE-X PCS/PMA or SGMII v9.1
UG155 March 24, 2008
Chapter 11: Dynamic Switching of 1000BASE-X and SGMII Standards R
Operation of the Core
Selecting the Power-On / Reset Standard
The external port of the core, basex_or_sgmii (see “Dynamic Switching Signal Pinout”
in Chapter 2 ), will select the default standard of the core as follows:
•
Tie to logic ‘0’ in the core instantiation. The core powers-up and comes out of a reset
cycle operating in the 1000BASE-X standard.
•
Tie to logic ‘1’ in the core instantiation. The core powers-up and comes out of a reset
cycle operating in the SGMII standard.
The basex_or_sgmii port of the core could be dynamically driven. In this configura-
tion, it is possible to drive a logical value onto the port, followed by a core reset cycle to
switch the core to the desired standard. However, it is expected that the standard will be
switched through the MDIO Management Registers.
Switching the Standard Using MDIO
The 1000BASE-X or SGMII standard of the core can be switched at any time by writing to
the
“Vendor-specific Register: Standard Selection Register (Register 17).” Following
completion of this write, the MDIO Management Registers will immediately switch.
•
Core set to 1000BASE-X standard. Management Registers 0 through 16 should be
interpreted according to
“1000BASE-X Standard Using the Optional Auto-
Negotiation,” page 119 .
•
Core set to SGMII standard. Management Registers 0 through 16 should be
interpreted according to
“SGMII Standard Using the Optional Auto-Negotiation,”
page 135 .
Auto-Negotiation State Machine
•
Core set to the 1000BASE-X standard. The Auto-Negotiation state machine operates as
described in
“1000BASE-X Standard,” page 156 .
•
Core set to perform the SGMII standard. The Auto-Negotiation state machine
operates as described in
“SGMII Standard,” page 156 .
•
Standard is switched during an Auto-Negotiation sequence. The Auto-Negotiation
state machine will not immediately switch standards, but attempt to continue to
completion at the original standard.
•
Switching the standard using MDIO. This does not cause Auto-Negotiation to
automatically restart. Xilinx recommends that after switching to a new standard using
a MDIO write, immediately perform the following:
♦ If you have switched to the 1000BASE-X standard, reprogram the Auto-
Negotiation Advertisement Register (Register 4) to the desired settings.
♦ For either standard, restart the Auto-Negotiation sequence by writing to bit 0.9 of
the MDIO Control Register (Register 0).
Setting the Auto-Negotiation Link Timer
As described in “Auto-Negotiation” in Chapter 10 , the duration of the Auto-Negotiation
Link Timer differs with the 1000BASE-X and the SGMII standards. To provide configurable
link timer durations for both standards, the following ports are available. These ports