netdev - Re: [PATCH] can: j1939: convert PGN structure to a table

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Date:   Tue, 27 Oct 2020 12:27:37 +0100
From:   Yegor Yefremov <yegorslists@...glemail.com>
To:     Marc Kleine-Budde <mkl@...gutronix.de>,
        Yegor Yefremov <yegorslists@...glemail.com>,
        linux-can@...r.kernel.org, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] can: j1939: convert PGN structure to a table

On Thu, Oct 22, 2020 at 2:25 PM Kurt Van Dijck
<dev.kurt@...dijck-laurijssen.be> wrote:
>
> On Thu, 22 Oct 2020 12:33:45 +0200, Marc Kleine-Budde wrote:
> > On 10/22/20 12:29 PM, yegorslists@...glemail.com wrote:
> > > From: Yegor Yefremov <yegorslists@...glemail.com>
> > >
> > > Use table markup to show the PGN structure.
> > >
> > > Signed-off-by: Yegor Yefremov <yegorslists@...glemail.com>
> > > ---
> > >  Documentation/networking/j1939.rst | 12 ++++++++----
> > >  1 file changed, 8 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/Documentation/networking/j1939.rst b/Documentation/networking/j1939.rst
> > > index faf2eb5c5052..f3fb9d880910 100644
> > > --- a/Documentation/networking/j1939.rst
> > > +++ b/Documentation/networking/j1939.rst
> > > @@ -71,10 +71,14 @@ PGN
> > >
> > >  The PGN (Parameter Group Number) is a number to identify a packet. The PGN
> > >  is composed as follows:
> > > -1 bit  : Reserved Bit
> > > -1 bit  : Data Page
> > > -8 bits : PF (PDU Format)
> > > -8 bits : PS (PDU Specific)
> > > +
> > > +  ============  ==============  ===============  =================
> > > +  PGN
> > > +  ----------------------------------------------------------------
> > > +  25            24              23 ... 16        15 ... 8
> >
> > ICan you add a row description that indicated that these numbers are. They are
> > probably bit positions within the CAN-ID?
>
> This is true for up to 99.9%, depending on who you ask.
> this maps indeed to the bit positions in the CAN-ID, as in J1939-21.
> The trouble is that PGN's are also communicated as such in the payload,
> e.g. in the TP and ETP (see J1939-81 if i remember correctly).
> Since only PGN is written there, without SA, the bit position relative
> to the CAN-ID are ... making things look fuzzy.
>
> So I the best I can propose is to add a 2nd row :-)

I have sent v2. Should I also include the tables for PDU1 and PDU2
formats as well as the general table with ID and Data? See Wiki [1]

[1] https://de.wikipedia.org/wiki/SAE_J1939#/media/Datei:J1939_Aufsplittung_CAN-Identifier.png

Best regards,
Yegor

> >
> > > +  ============  ==============  ===============  =================
> > > +  R (Reserved)  DP (Data Page)  PF (PDU Format)  PS (PDU Specific)
> > > +  ============  ==============  ===============  =================
> > >
> > >  In J1939-21 distinction is made between PDU1 format (where PF < 240) and PDU2
> > >  format (where PF >= 240). Furthermore, when using the PDU2 format, the PS-field
> > >
> >
> > Marc
> >
> > --
> > Pengutronix e.K.                 | Marc Kleine-Budde           |
> > Embedded Linux                   | https://www.pengutronix.de  |
> > Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
> > Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |
> >
>
>
>