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authorYegor Yefremov <yegorslists@googlemail.com>2020-11-04 18:57:30 +0300
committerMarc Kleine-Budde <mkl@pengutronix.de>2020-11-20 11:43:29 +0300
commitb7d3c0e5930deb3c8f69d7572e17baf2f07c56db (patch)
tree16fdc0094f1f9e8eff7b4a714139477bb550f5a3 /Documentation/networking/j1939.rst
parent4082c502bf9c8a6afe4268c654d4e93ab7dfeb69 (diff)
downloadlinux-b7d3c0e5930deb3c8f69d7572e17baf2f07c56db.tar.xz
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>
Diffstat (limited to 'Documentation/networking/j1939.rst')
-rw-r--r--Documentation/networking/j1939.rst46
1 files changed, 42 insertions, 4 deletions
diff --git a/Documentation/networking/j1939.rst b/Documentation/networking/j1939.rst
index 0a4b73b03b99..b705d2801e9c 100644
--- a/Documentation/networking/j1939.rst
+++ b/Documentation/networking/j1939.rst
@@ -69,18 +69,56 @@ J1939 concepts
PGN
---
+The J1939 protocol uses the 29-bit CAN identifier with the following structure:
+
+ ============ ============== ====================
+ 29 bit CAN-ID
+ --------------------------------------------------
+ Bit positions within the CAN-ID
+ --------------------------------------------------
+ 28 ... 26 25 ... 8 7 ... 0
+ ============ ============== ====================
+ Priority PGN SA (Source Address)
+ ============ ============== ====================
+
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
+ ------------------------------------------------------------------
+ Bit positions within the CAN-ID
+ ------------------------------------------------------------------
+ 25 24 23 ... 16 15 ... 8
+ ============ ============== ================= =================
+ 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
contains a so-called Group Extension, which is part of the PGN. When using PDU2
format, the Group Extension is set in the PS-field.
+ ============== ========================
+ PDU1 Format (specific) (peer to peer)
+ ----------------------------------------
+ Bit positions within the CAN-ID
+ ----------------------------------------
+ 23 ... 16 15 ... 8
+ ============== ========================
+ 00h ... EFh DA (Destination address)
+ ============== ========================
+
+ ============== ========================
+ PDU2 Format (global) (broadcast)
+ ----------------------------------------
+ Bit positions within the CAN-ID
+ ----------------------------------------
+ 23 ... 16 15 ... 8
+ ============== ========================
+ F0h ... FFh GE (Group Extenstion)
+ ============== ========================
+
On the other hand, when using PDU1 format, the PS-field contains a so-called
Destination Address, which is _not_ part of the PGN. When communicating a PGN
from user space to kernel (or vice versa) and PDU2 format is used, the PS-field