156
www.xilinx.com
Ethernet 1000BASE-X PCS/PMA or SGMII v9.1
UG155 March 24, 2008
Chapter 10:
Auto-Negotiation
R
Setting the Configurable Link Timer
The optional Auto-Negotiation function has a Link Timer (
link_timer[8:0]
) port. This
port sets the period of the Auto-Negotiation Link Timer. This port should be permanently
tied to a logical binary value, and a binary value should be placed on this port. The
duration of the timer is approximately equal to the binary value multiplied by 32.768
microseconds (4,96 clock periods of the 125 MHz clock provided to the core). See
“Auto-
Negotiation Signal Pinout” in Chapter 2
.
Note:
See
Chapter 11, “Dynamic Switching of 1000BASE-X and SGMII Standards”
for details of
programming the Auto-Negotiation Link Timer when performing dynamic switching between
1000BASE-X and SGMI Standards.
The accuracy of this Link Timer is within the following range.
+0 to -32.768 microseconds
1000BASE-X Standard
The Link-Timer is defined as having a duration somewhere between 10 and 20
milliseconds. The example design delivered with the core sets the binary value as follows:
100111101 = 317 decimal
This corresponds to a duration of between 10.354 and 10.387 milliseconds.
SGMII Standard
The Link-Timer is defined as having a duration of 1.6 milliseconds. The example design
delivered with the core sets the binary value to
000110010 = 50 decimal
This corresponds to a duration of between 1.606 and 1.638 milliseconds.
Simulating Auto-Negotiation
Auto-Negotiation requires a minimum of three link timer periods for completion. If
simulating the Auto-Negotiation procedure, setting the
link_timer[8:0]
port to a low
value will greatly reduce the simulation time required to complete Auto-Negotiation.
Using the Auto-Negotiation Interrupt
The Auto-Negotiation function has an
an_interrupt
port. This is designed to be used
with common micro-processor bus architectures (for example, the CoreConnect bus
interfacing to MicroBlaze or the Virtex-II Pro embedded IBM PowerPC). For more
information, see
“Auto-Negotiation Signal Pinout” in Chapter 2
.
The operation of this port is enabled or disabled and cleared via the MDIO Register 16, the
Vendor-specific Auto-Negotiation Interrupt Control Register.
•
When disabled, this port is permanently tied to logic 0.
•
When enabled, this port will be set to logic 1 following the completion of an Auto-
Negotiation cycle. It will remain high until it is cleared by writing 0 to bit 16.1
(Interrupt Status bit) of the
“MDIO Register 16: Vendor Specific Auto-Negotiation
Interrupt Control,” page 129
.
