From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 47124C64E8A for ; Fri, 20 Nov 2020 13:34:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 00E7A22272 for ; Fri, 20 Nov 2020 13:34:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728162AbgKTNda (ORCPT ); Fri, 20 Nov 2020 08:33:30 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51692 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728111AbgKTNd1 (ORCPT ); Fri, 20 Nov 2020 08:33:27 -0500 Received: from metis.ext.pengutronix.de (metis.ext.pengutronix.de [IPv6:2001:67c:670:201:290:27ff:fe1d:cc33]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F161AC061A48 for ; Fri, 20 Nov 2020 05:33:25 -0800 (PST) Received: from gallifrey.ext.pengutronix.de ([2001:67c:670:201:5054:ff:fe8d:eefb] helo=blackshift.org) by metis.ext.pengutronix.de with esmtp (Exim 4.92) (envelope-from ) id 1kg6XR-0006Fn-6F; Fri, 20 Nov 2020 14:33:21 +0100 From: Marc Kleine-Budde To: netdev@vger.kernel.org Cc: davem@davemloft.net, kuba@kernel.org, linux-can@vger.kernel.org, kernel@pengutronix.de, Yegor Yefremov , Marc Kleine-Budde Subject: [net-next 01/25] can: j1939: add tables for the CAN identifier and its fields Date: Fri, 20 Nov 2020 14:32:54 +0100 Message-Id: <20201120133318.3428231-2-mkl@pengutronix.de> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201120133318.3428231-1-mkl@pengutronix.de> References: <20201120133318.3428231-1-mkl@pengutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-SA-Exim-Connect-IP: 2001:67c:670:201:5054:ff:fe8d:eefb X-SA-Exim-Mail-From: mkl@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-can@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-can@vger.kernel.org From: Yegor Yefremov 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 Link: https://lore.kernel.org/r/20201104155730.25196-1-yegorslists@googlemail.com [mkl: removed trailing whitespace] Signed-off-by: Marc Kleine-Budde --- Documentation/networking/j1939.rst | 46 +++++++++++++++++++++++++++--- 1 file 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 base-commit: 4082c502bf9c8a6afe4268c654d4e93ab7dfeb69 -- 2.29.2