On Thu, 22 Oct 2020 12:33:45 +0200, Marc Kleine-Budde wrote: > On 10/22/20 12:29 PM, yegorslists@xxxxxxxxxxxxxx wrote: > > From: Yegor Yefremov <yegorslists@xxxxxxxxxxxxxx> > > > > Use table markup to show the PGN structure. > > > > Signed-off-by: Yegor Yefremov <yegorslists@xxxxxxxxxxxxxx> > > --- > > 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 :-) > > > + ============ ============== =============== ================= > > + 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 | >
