VSC7440 datasheet(288/444 Pages) MICROSEMI

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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

271

Insertion of the IFH can be configured on any port, but it is intended for frames forwarded to the internal

CPU and the NPI port (external CPU). When IFH insertion is enabled on a given port, all frames leaving

that port contain the IFH.

The following table lists the registers for configuring the insertion of extraction IFH into the frame.

The following illustration shows supported formats using KEEP_IFH_SEL.

Figure 82 •

Supported KEEP_IFH_SEL Formats

Frames are always formatted using KEEP_IFH_SEL = 1 when extracting frames to the internal CPU

ports. This cannot be changed.

Note that for KEEP_IFH_SEL = 1, the frames transmitted on external ports are not valid Ethernet frames,

because the extraction IFH precedes the DMAC. As a result, this frame format must be used for direct

transmission to another VSC7440 device that understands the format or to a dedicated FPGA or NPU.

This format cannot be used for forwarding to a standard Ethernet device.

The frame formats using KEEP_IFH_SEL = 2 or KEEP_IFH_SEL = 3 are primarily used on a port that is

directly attached to an external CPU. When the IFH is included using these frame formats, the IFH is

included in the frame’s FCS calculation and a valid Ethernet frame is transmitted.

3.26.14 Frame Injection from Internal CPU

To instruct the switch core how to process the frame, the internal CPU injects frames to switch core using

the internal frame header. The format of injected frames from the internal CPU is similar to the

KEEP_IFH_SEL = 1 format.

On arrival to the rewriter, such injected frames are no different from any other frames. However, the IFH

contains information related to rewriter functionality specifically targeting efficient frame injection:

•

Do not rewrite (IFH.FWD.DO_NOT_REW):

If this injection IFH bit is set, the rewriter forward frames unchanged to the egress port no matter any

other rewriter configurations, except IFH.FWD.update_fcs.

Table 191 •

IFH Configuration Registers

Description

Replication

PORT_CTRL.KEEP_IFH_SEL Configures the rewriter IFH mode for the port. See also

ASM::PORT_CFG.INJ_FORMAT_CFG.

0: Normal mode.

1: Keep IFH without modifications. Frames are not updated. IFH is

kept.

2: Encapsulate IFH. The frame’s DMAC, SMAC and a fixed TAG with

ETYPE = 8880 (Microsemi) and EPID=0x0009 are inserted in front of

the IFH: [FRM_DMAC][FRM_SMAC][0x8880][0x0009][IFH][FRAME].

3: Encapsulate IFH using the ENCAP table. Use ES0 to generate an

ENCAP_ID and insert the encapsulation in front of the

IFH:[ENCAP][IFH][FRAME].

Ports

IFH

Rewriter

Payload

IFH

Rewrite frame

IFH

Payload

Microsemi EtherType

and Protocol ID

KEEP_IFH_SEL = 3

KEEP_IFH_SEL = 2

KEEP_IFH_SEL = 1

KEEP_IFH_SEL = 0

IFH

Payload

Encapsulation

(ES0.ENCAP_ID)

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