KS8893ML MICREL [Micrel Semiconductor], KS8893ML Datasheet - Page 38

• Manufacturer Part Number: KS8893ML
• Description: Integrated 3-Port 10/100 Managed Switch with PHYs Preliminary Data Sheet Rev. 1.0
• Manufacturer: MICREL [Micrel Semiconductor]

Special Tagging Mode
Special Tagging Mode is designed for spanning tree protocol IGMP snooping and is flexible for use in other
applications. Special Tagging, similar to 802.1Q Tagging, requires software to change network drivers to
insert/modify/strip/interpret the special tag. This mode is enabled by setting both register 11 bit [0] and register 48
bit [2] to ‘1’.
The STPID is only seen and used by the port 3 interface, which should be connected to a processor. Packets
from the processor to the switch’s port 3 should be tagged with the STPID and the port mask, defined as follows:
Packets with normal tags (“0000” port masks) will use KS8893M internal MAC table lookup to determine the
forwarding port(s). Also, if packets from the processor are not tagged, the KS8893M will treat them as normal
packets and use internal MAC table lookup to determine the forwarding port(s).
The KS8893M uses a non-zero “port mask” to bypass the internal MAC table lookup result, and override any port
setting, regardless of port states (disable, blocking, listening, learning). The table below shows the processor to
switch egress rules when dealing with STPID.
June 2005
Ingress Tag Field
(0x810+ port mask)
(0x810+ port mask)
(0x810+ port mask)
(0x810+ port mask)
Not Tagged
“0001”, forward packet to port 1 only
“0010”, forward packet to port 2 only
“0011”, broadcast packet to port 1 and port 2
TPID (tag protocol identifier, 0x8100) + TCI.
Table 11. STPID Egress Rules (Processor to Switch Port 3)
802.1Q Tag Format
TX port “tag
insertion”
0
0
1
1
Don’t care
Table 10. Special Tagging Mode Format
TX port “tag
removal”
0
1
0
1
Don’t care
38
STPID (special tag identifier, 0x810 +
4 bit for “port mask”) + TCI
Special Tag Format
Egress Action to Tag Field
- Modify tag field to 0x8100
- Recalculate CRC
- No change to TCI if not null VID
- Replace VID with ingress (port 3) port
- (STPID + TCI) will be removed
- Padding to 64 bytes if necessary
- Recalculate CRC
- Modify tag field to 0x8100
- Recalculate CRC
- No change to TCI if not null VID
- Replace VID with ingress (port 3) port
- Modify tag field to 0x8100
- Recalculate CRC
- No change to TCI if not null VID
- Replace VID with ingress (port 3) port
- Determined by the Dynamic MAC
VID if null VID
VID if null VID
VID if null VID
Address Table
M9999-063005