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Functional Descriptions

VMDS-10488 VSC7511 Datasheet Revision 4.2

150

3.15.2

VRAP Response Frame Format

Having processed a VRAP request frame by executing the register access commands contained in the

frame, the VRAP engine generates a VRAP response frame. The response frame uses the swapped

DMAC and SMAC addresses in the VRAP request frame and it is transmitted on port where the VRAP

request frame was received. If the DMAC in the VRAP request frame is a multicast DMAC, then bit 40 is

cleared before using the DMAC as the SMAC in the VRAP response frame. The results of the VRAP

commands are inserted into the response frame in the same order as the VRAP commands were

processed.

The following illustration shows the format of a VRAP response frame.

Figure 47 •

VRAP Response Frame Format

The VRAP response frame follows the VRAP request frame in terms of VLAN tagging: If the VRAP request was

tagged, the VRAP response is also tagged using the same VLAN.

Only the READ and IDLE commands require data to be returned to the transmitter of the VRAP request

frame. However, even if the VRAP request frame does not contain READ and IDLE commands, a VRAP

response frame is generated with enough padding data (zeros) to fulfill the minimum transfer unit size.

3.15.3

VRAP Header Format

Both VRAP request and VRAP response frames contain a 32-bit VRAP header. The VRAP header is

used to identify the protocol version and to differentiate between VRAP requests and VRAP response

frames. The device supports VRAP version 1. The following illustration shows the VRAP header.

Figure 48 •

VRAP Header Format

A valid VRAP request frame must use Version = 1 and Flags.R = 1. Frames with an invalid VRAP header

are discarded and not processed by the VRAP engine.

3.15.4

VRAP READ Command

The VRAP READ command returns the contents of any 32-bit register inside the device. The 32-bit read-

data result is put into the VRAP response frame.

READ and IDLE results

SMAC from

VRAP request frame

0x8880

DMAC

DMAC from VRAP

request frame

SMAC

0x0004

EtherType

EPID

Valid FCS

FCS

16 bits

48 bits

32 bits

variable length

VRAP HDR

(Response)

32 bits

Version

4 bits

Flags

Reserved

4 bits

24 bits

Version:

Set to 0x1 in VRAP response frames.

VRAP request frames are ignored if Version <> 1

Flags:

4 bits are used for Flags. Only one flag is defined:

R: 0=Request, 1=Response

Rsv: Set to 0 in VRAP response frames and ignored in VRAP

request frames.

Reserved:

Set to 0 in VRAP response frames and ignored in VRAP

request frames.

28 27

24 23

Rsv

VSC7511 Datasheet(PDF) 165 Page - Microsemi Corporation

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