Intel GD82559ER manual Description, Parallel Detect and Auto-Negotiation, Datasheet

GD82559ER — Networkin g Silicon

6.3.1Description

Auto-Negotiation selects the fastest operating mode (in other words, the highest common denominator) available to hardware at both ends of the cable. A PHY’s capability is encoded by bursts of link pulses called Fast Link Pulses (FLPs). Connection is established by FLP exchange and handshake during link initialization time. Once the link is established by this handshake, the native link pulse scheme resumes (that is, 10BASE-T or 100BASE-TX link pulses). A reset or management renegotiate command (through the MDI interface) will restart the process. To enable Auto-Negotiation, bit 12 of the MDI Control Register must be set. If the PHY unit cannot perform Auto-Negotiation, it will set this bit to a 0 and determine the speed using Parallel Detection.

The PHY unit supports four technologies: 100BASE-Tx Full and Half Duplex and 10BASE-T Full and Half Duplex. Since only one technology can be used at a time (after every re-negotiate command), a prioritization scheme must be used to ensure that the highest common denominator ability is chosen. Each bit in this table is set according to what the PHY is capable of supporting. In the case of the 82559’s PHY unit, bits 0, 1, 2, 3, and 5 (10BASE-T, 10BASE-T full duplex, 100BASE-TX, 100BASE-TX full duplex and pause [frame based flow control], respectively) are set.

To detect the correct technology, the two register fields, technology ability and technology priority, should be ANDed together to obtain the highest common denominator. This value should then be used to map into a priority resolution table used by the MAC driver to use the appropriate technology.

6.3.2Parallel Detect and Auto-Negotiation

The PHY unit automatically determines the speed of the link either by using Parallel Detect or Auto-Negotiation. Upon a reset, a link status fail, or a Negotiate/Re-negotiate command, the PHY unit inserts a long delay during which no link pulses are transmitted. This period, known as Force_Fail, insures that the PHY unit‘s link partner has gone into a Link Fail state before Auto- Negotiation or Parallel Detection begins. Thus, both sides (PHY unit and PHY unit’s link partner)

44 Datasheet