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Functional Descriptions

VMDS-10488 VSC7511 Datasheet Revision 4.2

107

The IS1 action FID_SEL selects whether to use the FID_VAL for the DMAC lookup, for the SMAC lookup

(learning), or for both lookups. If set for a lookup, the FID_VAL replaces the VID when calculating the

hash key into the MAC table and when comparing with the entry’s VID. If used during the SMAC lookup,

new entries are learned using the FID_VAL. If an IS1 action returns a FID_SEL > 0, it overrules the use

of the FID mapping table for the frame. In addition, FID_SEL > 0 overrules the use of the FID_MASK for

the MAC table lookups specified in FID_SEL.

The FID mapping table, FID_MAP, maps the frame’s classified VID to a FID. If the returned FID is larger

than 0, then the FID overrules the use of the FID_MASK for both the DMAC and SMAC lookups in the

MAC table. Learning is done using the returned FID.

If neither IS1 nor the FID_MAP table have instructed changes to the FID, then the FID_MASK is applied.

The 12-bit FID_MASK masks out the corresponding bits in the VID. The FID used for learning and lookup

is therefore calculated as FID = VID AND (NOT FID_MASK). The FID used in the MAC table is 13 bits so

the calculated FID is prepended with 0. Bit 13 in the FID in the MAC table is only selectable through the

FID_ENA action out of IS1.

All VIDs mapping to the same FID share the same MAC table entries.

Example: Configure all MAC table entries to be shared among all VLANs.

This is done by setting FID_MASK to 111111111111.

Example: Split the MAC table into two separate databases: one for even VIDs and one for odd VIDs.

This is done by setting FID_MASK to 111111111110.

3.9.1.8

Learn Limit

The following table lists the registers associated with controlling the number of MAC table entries per

port.

The ENTRYLIM.ENTRYLIM register specifies the maximum number of unlocked entries in the MAC table

that a port is allowed to use. Locked and IPMC entries are not taken into account.

After the limit is reached, both auto-learning and CPU-based learning on unlocked entries are denied. A

learn frame causing the limit to be exceeded can be copied to the CPU (PORT_CFG.LIMIT_CPU) and

the forwarding to other front ports can be denied (PORT_CFG.LIMIT_DROP).

The ENTRYLIM.ENTRYSTAT register holds the current number of entries in the MAC table. MAC table

aging and manual removing of entries through the CPU cause the current number to be reduced. If a

MAC table entry moves from one port to another port, this is also reduces the current number. If the

move causes the new port’s limit to be exceeded, the entry is denied and removed from the MAC table.

The LEARNDISC counts all events where a MAC table entry is not created or updated due to a learn

limit.

Table 80 •

Learn Limit Definition Registers

Description

Replication

ENTRYLIM

Configures maximum number of unlocked entries in the

MAC table per ingress port.

Per port

PORT_CFG.LIMIT_CPU

If set, learn frames exceeding the limit are copied to the

CPU.

Per port

PORT_CFG.LIMIT_DROP If set, learn frames exceeding the limit are discarded.

Per port

LEARNDISC

The number of MAC table entries that could not be

learned due to a lack of storage space.

None

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