IBM PowerPC 405GP User Manual

Figure 19-11 illustrates the Tagged MAC Frame format.
Preamble
SPD
DA
SA
Type=TPID
Preamble
- Alternating Os and 1s (7 bytes)
SPD (Start Of Packet Delimiter)1 byte
DA (Destination Address) 6 bytes
SA (Source Address) 6 bytes
TPID
(Tag Protocol Identifier, 2 bytes) = OxB100
TCI (Tag Control Information) 2 bytes
LengthlType 2 bytes
Data
(42-1500 l5ytes)
Pad (Optional field)
FCS - Calculated FCS
Tag
Control
Length/
Data
Type
Figure 19-11. Tagged MAC Packet Format
Figure 19-12 illustrates the structure of the TCI field.
7 6 5 4 3
o
Pad
FCS
VLAN Identifier I First Octet
7
o
L...-.. _____ V_L_A_N_ld_e_nt_ifi_er ______ --J1 Second Octel
CFI is a Canonical Format Indicator (always 1 for Ethernet media)
Figure 19-12. Tag Control Information Field Structure
19.6.1 VLAN Tagged Packet Transmission
When EMACO_MR1 [VLE] = 1, the following configuration options are available, depending on the
content of the appropriate bits in the MAL control word (see section 19.3.3.1 ,
"MAL TX Descriptor
Control/Status Field," on page 7):
• The Generate FCS bit (bit 6) is not set or both Insert VLAN Tag and Replace VLAN Tag bits (bits 10
and 11, respectively) are not set: EMAC transmits the packet without any changes
• Bit 6 is set and bit 10 is also set: EMAC will insert TPID and Tag control information for the
transmitting packet using the content of
EMACO_ VTPID and EMACO_ VTCI; respectively
• Bit 6 is set and bit 11 is also set: EMAC will replace TPID and Tag control information for the
transmitting packet using the content
of EMACO_ VTPID and EMACO_ VTCI, respectively
19.6.2 VLAN Tagged Packet Reception
If EMACO_MR1 [VLE] = 1, EMAC parses the VLAN Tag unique type/length in the incoming packet
during the receive process.
If the VLAN Tag is equal to the value stored in the EMACO_ VTPID, EMAC
Preliminary
Ethernet Media Access Controller 19-19

IBM PowerPC 405GP Specifications

General

Brand	IBM
Model	PowerPC 405GP
Category	Computer Hardware
Language	English