IBM PowerPC 405GP User Manual

discards all incoming packets and does not request data from the MAL for transmission. When a
magic packet is detected, the EMAC generates a
UIC interrupt on Interrupt 9, called Ethernet WOL.
19.2.6 Ethernet MAC
The Ethernet MAC logic supports the Media Independent Interface (Mil).
19.2.7 EMAC Loop-Back Modes
EMAC supports the external and internal loop-back modes illustrated in Figure 19-3~
Mil
External
Loop-back
Internal
Loop-back
EMAC
I
TXMAC
I
RXMAC
EMAC
TXMAC
RXMAC
~
I PHY
Figure 19-3. EMAC Loop-Back Modes
External loop-back mode uses the PHY device. To EMAC, external loop-back is identical to full-duplex
operation. Configuring EMAC to operate in a full-duplex mode enables external loop-back. EMAC
does not need an
external loop-back configuration signal.
In internal loop-back mode, data from the EMAC transmit channel is routed to the EMAC receive
channel. This loop-back mode functions correctly with or without a PHY connected to EMAC. In
internal loop-back
mode, EMAC does not activate (monitor) any Mil signals. The transmit channel
signals
are buffered internally to the receive channel. However, if internal loop-back is used without a
PHY, the TX and RX clocks for EMAC must be provided by another means. In internal loop-back
mode, the EMAC transmit clock and receive clock must be sourced from a single clock.
19.3 EMAC Transmit Operation
The transmit part of EMAC is responsible for packet transmission from the MAL device to the Mil
interface. At the end of the transmission process, EMAC provides a status/error word which allows
monitoring the transmission operation.
EMAC
implements dual transmit channels with MAL (this means that two transmit channels are
allocated within MAL) for efficient utilization of the Transmit
FIFO. Both of these channels use the
same shared resources inside EMAC. These
channels can be configured to independently request
packets from MAL and drive them into the TX
FIFO or act as a single channel (in dependent mode).
Preliminary
Ethernet Media Access Controller
19-5

IBM PowerPC 405GP Specifications

General

Brand	IBM
Model	PowerPC 405GP
Category	Computer Hardware
Language	English