AutoNegotiation
5-7
becoming full. A new MAC control layer was added to handle generation
and reception of Pause Frames. This control layer contains a timer
indicating the amount of Pause requested. Each MAC/Controller has to
advertise whether it can handle Pause Frames, and whether they support
Pause Frames in both directions (receive and transmit). If the
MAC/Controller only generates Pause Frames but does not respond to
Pause Frames generated by a link partner, this is called Asymmetrical
Pause. Advertisement of these capabilities can be achieved by writing a
1 to bits 10 and 11 of the
AutoNegotiation Advertisement Register
(ANAR) Address 0x04
. The link partners Pause capabilities can be
determined from
AutoNegotiation Link Partner Ability Register (ANLPAR)
Address 0x05
using these same bits. The MAC/controller has to write to
and read from these registers and determine which mode of Pause
operation to choose. The PHY layer is not involved in Pause resolution
other than the simple advertising and reporting of Pause capabilities
(these capabilities are MAC capabilities and configured by the MAC into
PHY registers).
5.3.4 AutoNegotiation Automatic MDIX Resolution
The L80600 can determine if a “straight” or “crossover” cable is being
used to connect to the link partner and can automatically reassign
channel A and channel B to establish link with the link partner. Although
not part of the AutoNegotiation FLP exchange process, the Automatic
MDIX resolution requires that AutoNegotiation is enabled. Automatic
MDIX resolution precedes the actual AutoNegotiation process, which
involves exchange of FLPs to advertise capabilities. If AutoNegotiation is
not enabled, the MDIX function can be manually configured by disabling
Automatic MDIX and forcing either a straight or a crossover cable
configuration. See
Chapter 9, “L80600 Frequently Asked Questions”
for
details.
5.3.5 AutoNegotiation Strap Option Control
The AutoNegotiation function within the L80600 can be controlled either
by internal register access or by the use of the AN_EN, and various strap
pin values during power-on/reset.
Table 5.4
shows how the various strap
pin values are used during AutoNegotiation to advertise different
capabilities.