Re: Link type FlexRay

[Guenter Ebermann <guenter.ebermann () googlemail com>]

2016-01-15 21:35 GMT+01:00 Guy Harris <guy () alum mit edu>:
> On Jan 15, 2016, at 10:44 AM, Guenter Ebermann <guenter.ebermann () googlemail com> wrote:
>
> I don't know whether Hannes still works at X2E.  You might want to try sending an e-mail to him asking whether a 
> format for DLT_FLEXRAY was ever defined - and, if it has, asking him to send me a copy so that I can add it to the 
> link-layer header types page:
>
>         http://www.tcpdump.org/linktypes.html
>
> (and, if any of the *others* were defined, to send those to me as well).
>
> If mail to him bounces, you could try contacting X2E to see if that information is available, or if they ever 
> supporting writing out files in pcap or pcapng format.
>
> If they never wrote files out with a link-layer header type of 210 for DLT_FLEXRAY/LINKTYPE_FLEXRAY, then you can use 
> it for your own purposes - send us the spec and I'll add it to the link-layer header types page.
>
> If they did, but they don't tell you what format they use, we can create a new LINKTYPE_/DLT_ value for your format, 
> and provide a public specification for that one.

I asked Hannes about DLT_FLEXRAY.
He told me that they currently dont use pcap for FlexRay and have only
used it in a limited scenario and that we are free to change the
layout.
The format represented the bitsream from the bus 1:1 without an
additional header.
The only deviation was the padding: the data was padded to align to 4
byte boundaries.

This is my suggestion for an extension:

I want to extend the frame by a "measurement-header": This header is
added by the measurement device. It contains one bit for the FlexRay
channel (A or B), a "data-type" enumeration and error-flags.

Error-flags will be all kind of decoding errors which may be detected
during capture of a FlexRay frame. That is: TSS, FSS, BSS, or FES
violations. Header CRC or Frame CRC errors and all kind of
"short-item-counts" that is, if not all bytes of the frame-bitstream
could be captured.

One enum-value of the "data-type" will be for a "data-frame", whereas
a data frame would have exactly the same coding as on the FlexRay bus.

The second enum-value of the "data-type" will be a "flexray-symbol",
which contains the bitlength information of the captured FlexRay
symbol (used for CAS and Wakeup).

BR
Günter
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