VSCP over Ethernet

VSCP can use Ethernet directly making it possible to construct very low end nodes. The payload is a standard VSCP level II frame with some specific Ethernet stuff in it

Content	Size	Description
Destination MAC address	6 bytes	Destination address
Source MAC address	6 bytes	Source address
Ethernet Type	2 bytes	Packet type
VSCP sub destination address	2 bytes	Lowest 16 bits of VSCP GUID destination address
VSCP sub source address	2 bytes	Lowest 16 bits of VSCP GUID source address
VSCP head	2 bytes	Header: To be defined
VSCP class	2 bytes	16-bit VSCP class
VSCP type	2 bytes	16-bit VSCP type
Payload	1- 512 bytes	VSCP data.
CRC	4-bytes	32 bit CRC checksum

The VSCP GUID for Ethernet is defined as

FF FF FF FF FF FF FF FE YY YY YY YY YY YY XX XX

where FF FF FF FF FF FF FF FE say this is an Enhernet GUID and YY YY YY YY YY YY is the MAC address and XX XX is the id for a specific VSCP device. Each node can thus appear as 65535 - 2 nodes which is perfect for a gateway or similar device that have VSCP devices connected on one or many other buses such as CAN, RF and the like. Two id's is reserved. 0 which is the Ethernet node itself and 0xffff which is all nodes on the interface. If a node consist just of itself then it can ignore the VSCP sub address but it is recommended that it use 0×0000 for it's transmitted frames.

More information on the Ethernet frames are here: http://en.wikipedia.org/wiki/Ethernet

The Ethernet type is still to be defined.

Standard Level read register operation

Level II

Content	Size	Description
Destination MAC address	6 bytes	Destination address - We know which node we want to talk to so this is a real MAC part of the nodes full GUID
Source MAC address	6 bytes	Source address - Always the MAC part of the GUID
Ethernet Type	2 bytes	Packet type
VSCP sub destination address	2 bytes	Lowest 16 bits of VSCP GUID destination address
VSCP sub source address	2 bytes	Lowest 16 bits of VSCP GUID source address
0×0000	2 bytes	Header: To be defined
0×0400	2 bytes	Level II Protocol Functionality
0×0001	2 bytes	ReadRegisterII
Register to read	4 bytes	Address for VSCP register to read.
Register count.	2 bytes	Number of consecutive registers to read
Reserved	2 bytes	Two nills.
GUID	16 bytes	GUID for the target node.
CRC	4-bytes	32 bit CRC checksum

The answer will be

Content	Size	Description
Destination MAC address	6 bytes	Destination address - We know which node did the read request so this is a real MAC part of the nodes full GUID
Source MAC address	6 bytes	Source address - Always the MAC part of the GUID
Ethernet Type	2 bytes	Packet type
VSCP sub destination address	2 bytes	Lowest 16 bits of VSCP GUID destination address
VSCP sub source address	2 bytes	Lowest 16 bits of VSCP GUID source address
VSCP head	2 bytes	Header: To be defined
0×0400	2 bytes	Level II Protocol Functionality
0×0003	2 bytes	ReadWriteResponseII
Register to read	4 bytes	Address for VSCP register to read.
Reserved	2 bytes	Two nills.
Register content	n bytes	Content for registers read.
CRC	4-bytes	32 bit CRC checksum

Note that the Ethernet node can act as a proxy for several subnets connected to it. These devices can have there own unique GUID's we can read from them but they are also known with the GUID of our Ethernet device but they will all have different VSCP sub addresses.

Think of a an Ethernet device with eight CAN buses connected to it. To the outer world it looks like an Ethernet device. This device can use the MSB of the VSCP sub address to address the segment and the LSB to represent a nickname id for a specific device on that bus. This way it is possible to address each device on each segment individually.

Level I

But it is perfectly fine to do a Level I read as well

Content	Size	Description
Destination MAC address	6 bytes	Destination address - We know which node we want to talk to so this is a real MAC part of the nodes full GUID
Source MAC address	6 bytes	Source address - Always the MAC part of the GUID
Ethernet Type	2 bytes	Paket type
VSCP sub destination address	2 bytes	Lowest 16 bits of VSCP GUID destination address
VSCP sub source address	2 bytes	Lowest 16 bits of VSCP GUID source address
0×0000	2 bytes	Header: To be defined
0×0000	2 bytes	Level I Protocol Functionality
0×0009	2 bytes	Read register.
Register to read	1 bytes	Address for VSCP register to read.
Node id	1 bytes	Nickname if for the node who's registers should be read
Register	1 bytes	Register to read
CRC	4-bytes	32 bit CRC checksum

this will get an answer

Content	Size	Description
Destination MAC address	6 bytes	Destination address - We know which node we want to talk to so this is a real MAC part of the nodes full GUID
Source MAC address	6 bytes	Source address - Always the MAC part of the GUID
Ethernet Type	2 bytes	Packet type
VSCP sub destination address	2 bytes	Lowest 16 bits of VSCP GUID destination address
VSCP sub source address	2 bytes	Lowest 16 bits of VSCP GUID source address
0×0000	2 bytes	Header: To be defined
0×0000	2 bytes	Level I Protocol Functionality
0x000A	2 bytes	Read/write register response.
Register read	1 bytes	Address for VSCP register read.
Content	1 bytes	Content of register.
CRC	4-bytes	32 bit CRC checksum

How about non addressed events

Non addressed events such as a temperature measurement is broadcasted on the bus using MAC address 0xFFFFFFFFFFFF. So a Temperature event can look like this

Content	Size	Description
Destination MAC address	6 bytes	Destination address - Broadcast = 0xFFFFFFFFFFFF
Source MAC address	6 bytes	Source address - Always the MAC part of the GUID
Ethernet Type	2 bytes	Packet type
VSCP sub destination address	2 bytes	Broadcast 0xFFFF
VSCP sub source address	2 bytes	Lowest 16 bits of VSCP GUID source address
0×0000	2 bytes	Header: To be defined
0x000A	2 bytes	Level I Measurement Functionality
0×0006	2 bytes	Temperature reading.
Datacoding	1 bytes	VSCP data coding byte.
value	1-7 bytes	Temperature.
CRC	4-bytes	32 bit CRC checksum

VSCP header

Description of the VSCP Ethernet package header.

Bits	Description
bit 15,14,13	Priority. 0 - highest, 7-lowest.
bit 12	Hardcoded. For compability with other physical protocols used by VSCP.
bit 11-0	Reserved

vscp/spec/phy/vscp_over_ethernet.txt · Last modified: 2009/11/26 12:24 by admin

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