IBM PowerPC 405GP User Manual

Table 19-3. FCSNLAN Tag Enable - Possible Configurations
Configuration Options EMAC Action
Insert VLAN Replace VLAN Insert VLAN Replace VLAN
Generate FCS
Tag
Tag
Add FCS Tag
Tag
1
1
0 Y
Y
N
19.4 EMAC Receive 'Operation
The receive part of EMAC is responsible for receiving packets coming from the physical layer (PHY)
device and forwarding them to the receive
channel of the attached MAL. At the end of the reception
process, EMAC provides a status/error word which
allows software to monitor the receive operation.
19.4.1 EMAC - MAL RX Packet Transfer Flow
EMAC initiates request for service from MAL whenever the number of occupied entries in the Receive
FIFO reaches the low water mark specified in EMACO_RWMR[RLWM].
19.4.2 MAL RX Descriptor Status
For each packet that is received, MAL obtains status from EMAC after reception is complete, and
writes this information into the buffer descriptor status/control
field. Software uses this information to
monitor the status of received packets.
See "Buffer Descriptor Overview" on page 20-7 for more
information on the buffer descriptor structure.
o 2 3 4 5 6 7 8 9 10 11 12 13 14 15
I MAL I MAL I MAL I MAL I ~,1AL I ~.1AL I . I· . I· . I . I· . I' . I
,/, /
V V
MAL usage EMAC specific control/status - for software handling
Figure 19-6. MAL RX Descriptor Control/Status Field ,
Bits Bit Name
Bit Description Mode
0 .. 5
MAL Usage
See "RX Status/Control Field Format" on page 20-16. R
RX
Status Information (Read Access)
6
Overrun Error
o No overrun error. R
1 EMAC detected an overrun error.
An overrun error occurs if the flow of received data to the RX
FIFO is corrupted because of insufficient empty space.
7 Pause Packet o Received packet is not a control pause packet. R
1 Received packet is a control pause packet.
8
Bad Packet
o No packet errors. R
1 Early termination caused by packet error.
9
Runt
Packet o Duration of PHY _RX_DV signal OK.
R
1 Duration of
PHY _RX_DV signal greater than ShortEventMax
Time constant and less than collision windows.
19-12
PPC405GP User's Manual Preliminary

IBM PowerPC 405GP Specifications

General

Brand	IBM
Model	PowerPC 405GP
Category	Computer Hardware
Language	English