Setting the configurable link timer, 1000base-x standard, Sgmii standard – Xilinx 1000BASE-X User Manual

Page 156: Simulating auto-negotiation, Using the auto-negotiation interrupt, Using the auto, Setting the

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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

.

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