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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

291

Each of the VRAP commands are described in the following sections. Each VRAP request frame can

contain multiple VRAP commands. Commands are processed sequentially starting with VRAP command

1, 2, and so on. There are no restrictions on the order or number of commands in the frame.

3.30.2

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.

3.30.3

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. 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.

The following illustration shows the VRAP header.

Figure 88 •

VRAP Header Format

3.30.4

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.

The READ command is 4 bytes wide and consists of one 32-bit address field, which is 32-bit aligned. The

2 least significant bits of the address set to 01. The following illustration shows the request command and

the associated response result.

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

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