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can: j1939: add tables for the CAN identifier and its fields
Use table markup to show the structure of the CAN identifier, PGN, PDU1, and
PDU2 formats. Also add introductory sentence.
Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Link: https://lore.kernel.org/r/20201104155730.25196-1-yegorslists@googlemail.com
[mkl: removed trailing whitespace]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
authored by
Yegor Yefremov
and committed by
Marc Kleine-Budde
b7d3c0e5
4082c502
+42
-4
+42
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Documentation/networking/j1939.rst
+42
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Documentation/networking/j1939.rst
···
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PGN
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---
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The J1939 protocol uses the 29-bit CAN identifier with the following structure:
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============ ============== ====================
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29 bit CAN-ID
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--------------------------------------------------
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Bit positions within the CAN-ID
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--------------------------------------------------
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28 ... 26 25 ... 8 7 ... 0
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============ ============== ====================
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Priority PGN SA (Source Address)
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============ ============== ====================
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The PGN (Parameter Group Number) is a number to identify a packet. The PGN
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is composed as follows:
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-
1 bit : Reserved Bit
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1 bit : Data Page
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8 bits : PF (PDU Format)
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8 bits : PS (PDU Specific)
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============ ============== ================= =================
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PGN
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------------------------------------------------------------------
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Bit positions within the CAN-ID
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------------------------------------------------------------------
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25 24 23 ... 16 15 ... 8
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============ ============== ================= =================
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R (Reserved) DP (Data Page) PF (PDU Format) PS (PDU Specific)
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============ ============== ================= =================
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In J1939-21 distinction is made between PDU1 format (where PF < 240) and PDU2
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format (where PF >= 240). Furthermore, when using the PDU2 format, the PS-field
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contains a so-called Group Extension, which is part of the PGN. When using PDU2
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format, the Group Extension is set in the PS-field.
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============== ========================
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PDU1 Format (specific) (peer to peer)
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----------------------------------------
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Bit positions within the CAN-ID
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----------------------------------------
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23 ... 16 15 ... 8
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============== ========================
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00h ... EFh DA (Destination address)
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============== ========================
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============== ========================
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PDU2 Format (global) (broadcast)
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----------------------------------------
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Bit positions within the CAN-ID
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----------------------------------------
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23 ... 16 15 ... 8
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============== ========================
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F0h ... FFh GE (Group Extenstion)
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============== ========================
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On the other hand, when using PDU1 format, the PS-field contains a so-called
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Destination Address, which is _not_ part of the PGN. When communicating a PGN