Intel PCI-X manual Gmii 1 Gb/s, Code Groups and Ordered Sets, Code Group and Ordered Set Usage

Ethernet Interface

8.2.1.3Code Groups and Ordered Sets

Code group and ordered set definitions are defined in clause 36 of the IEEE 802.3z standard. These represent special symbols used in the encapsulation of Gigabit Ethernet packets. Table 8-1lists a brief description of defined ordered sets for informational purposes only.

Table 8-1. Code Group and Ordered Set Usage

Code	Ordered_Set	# of Code	Usage
		Groups
			General reference to configuration ordered sets, either
			/C1/ or /C2/, which is used during Auto Negotiation to
/C/	Configuration	4	advertise & negotiate link operation information between
			link partners. Last two code groups contain config base
			and next page registers.
/C1/	Configuration 1	4	See /C/. Differs from /C2/ in second code group for
			maintaining proper signaling disparity.
/C2/	Configuration 2	4	See /C/. Differs from /C1/ in second code group for
			maintaining proper signaling disparity.
			General reference to IDLE ordered sets. IDLE characters
			are continually transmitted by the end stations and are
/I/	IDLE	2	replaced by encapsulated packet data. The transitions in
			the IDLE stream allow the SerDes to maintain clock and
			symbol synchronization between to link partners.
/I1/	IDLE 1	2	See /I/. Differs from /I2/ in second code group for
			maintaining proper signaling disparity.
/I2/	IDLE 2	2	See /I/. Differs from /I1/ in second code group for
			maintaining proper signaling disparity.
			This ordered set is used to indicate carrier extension to
/R/	Carrier_Extend	1	the receiving PCS. It is also used as part of the
			end_of_packet encapsulation delimiter as well as IPG for
			packets in a burst of packets.
			The SPD (start_of_packet delimiter) ordered set is used to
/S/	Start_of_Packet	1	indicate the starting boundary of a packet transmission.
			This symbol replaces the last byte of the preamble
			received from the MAC layer.
			The EPD (end_of_packet delimiter) is comprised of three
/T/	End_of_Packet	1	ordered sets. The /T/ symbol is always the first of these
			and indicates the ending boundary of a packet.
			The /V/ ordered set is used by the PCS to indicate error
/V/	Error_Propagation	1	propagation between stations. This is normally intended to
			be used by repeaters to indicate collisions.

8.2.2GMII – 1 Gb/s

The internal Gigabit Media Independent Interface (GMII) is similar to the 10/100 Mb/s Media Independent Interface (MII). The GMII uses the MII management interface and registers. These common elements of operation allow the Ethernet controller to determine PHY capabilities for any supported speed of operation and configuration of the hardware based on those capabilities.

Most of the MII and GMII signals use the same names, but the width of the RX and TX data busses and the semantics of the associated control signals differ between MII and GMII operation. The GMII transmit path clocking also differs significantly from MII clocking.

Software Developer’s Manual 155