Talk:SpaceWire

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The link to reference 6: "Space Packet Transfer Protocol" (PDF). appears to be stale

When I click on it I get an 404 Not found error. Maybe update the link or remove it.

What is the delimiter of address and cargo ?

Latest comment: 11 months ago3 comments3 people in discussion

Hi
I'm try to understand (private interest) the SpaceWire protocol. There are a few documents, but I can't find how to distinguish between address and cargo. On http://spacewire.esa.int tdefintion is:

<Destination Address><Cargo><End_of_Packet>

Also all official documentes just talking about address resp. cargo but never what the delimiter or other attributes are. Not even wiki can tell me :-)
Any idea?-- Istiller (talk) —Preceding undated comment added 13:14, 4 September 2015 (UTC)Reply

ECSS standard: Since there is no start_of_packet marker, the first data character following an end_of_packet marker (either EOP or EEP) is regarded as the start of the next packet. The control codes (EOP or EEP here) are distinguished from ordinary bytes by means of special additional prefix bits. Regards, Marek P. 80.250.30.194 (talk) 15:58, 28 December 2015 (UTC)Reply

From what I've read about SpaceWire (and the technologies it uses -- IEEE 1355 and Wormhole switching, etc.),

My understanding is that it's impossible (and unnecessary) to distinguish between address and cargo -- there is no delimiter between them.

As Merek said, there is a way to distinguish between the 256 data characters (which are also re-used as destination address characters) and a few other special characters used as link control characters.

When a packet enters a router (via some input port), the router only investigates the first character in the packet to decide which port to send (the rest of) that packet out. The router neither knows nor cares how many of the *following* data characters are actually further address characters.

If that output port happens to be *another* router, then the next data character will be interpreted by *that* router as an address character; but if that output port happens to be connected to some endpoint peripheral, then the same data character will be interpreted by that peripheral as some sort of cargo data.

The rest of the data characters that come in through that input port are blindly copied to that same output port, until the special "end of packet" link control character (which is *different* than any of the 256 data characters) is copied out that output port, marking the end of that packet.

The "first character in the packet" is identified by the router as the first data character (i.e., the first non-link-control character) *after* an end-of-packet link-control character.

How could we make this more clear in this article or the IEEE 1355 article? --DavidCary (talk) 06:11, 14 November 2023 (UTC)Reply

External links modified (January 2018)

Latest comment: 6 years ago1 comment1 person in discussion

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