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Message-ID: <CAGm1_kuZkrbaLwATrbPkmDmQW7SAwDapy5jbT8EwOSmccGqV0A@mail.gmail.com>
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 |
> >
>
>
>
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