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can: j1939: fix syntax and spelling
This patches fixes the syntax an spelling of the j1939 documentation.
Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Link: https://lore.kernel.org/r/20201020101043.6369-1-yegorslists@googlemail.com
Fixes: 9d71dd0c70
("can: add support of SAE J1939 protocol")
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
This commit is contained in:
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@ -10,9 +10,9 @@ Overview / What Is J1939
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SAE J1939 defines a higher layer protocol on CAN. It implements a more
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sophisticated addressing scheme and extends the maximum packet size above 8
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bytes. Several derived specifications exist, which differ from the original
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J1939 on the application level, like MilCAN A, NMEA2000 and especially
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J1939 on the application level, like MilCAN A, NMEA2000, and especially
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ISO-11783 (ISOBUS). This last one specifies the so-called ETP (Extended
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Transport Protocol) which is has been included in this implementation. This
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Transport Protocol), which has been included in this implementation. This
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results in a maximum packet size of ((2 ^ 24) - 1) * 7 bytes == 111 MiB.
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Specifications used
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@ -32,15 +32,15 @@ sockets, we found some reasons to justify a kernel implementation for the
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addressing and transport methods used by J1939.
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* **Addressing:** when a process on an ECU communicates via J1939, it should
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not necessarily know its source address. Although at least one process per
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not necessarily know its source address. Although, at least one process per
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ECU should know the source address. Other processes should be able to reuse
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that address. This way, address parameters for different processes
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cooperating for the same ECU, are not duplicated. This way of working is
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closely related to the UNIX concept where programs do just one thing, and do
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closely related to the UNIX concept, where programs do just one thing and do
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it well.
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* **Dynamic addressing:** Address Claiming in J1939 is time critical.
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Furthermore data transport should be handled properly during the address
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Furthermore, data transport should be handled properly during the address
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negotiation. Putting this functionality in the kernel eliminates it as a
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requirement for _every_ user space process that communicates via J1939. This
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results in a consistent J1939 bus with proper addressing.
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@ -58,7 +58,7 @@ Therefore, these parts are left to user space.
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The J1939 sockets operate on CAN network devices (see SocketCAN). Any J1939
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user space library operating on CAN raw sockets will still operate properly.
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Since such library does not communicate with the in-kernel implementation, care
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Since such a library does not communicate with the in-kernel implementation, care
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must be taken that these two do not interfere. In practice, this means they
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cannot share ECU addresses. A single ECU (or virtual ECU) address is used by
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the library exclusively, or by the in-kernel system exclusively.
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@ -77,13 +77,13 @@ is composed as follows:
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8 bits : PS (PDU Specific)
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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 PDU2 format, the PS-field
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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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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
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from user space to kernel (or visa versa) and PDU2 format is used, the PS-field
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from user space to kernel (or vice versa) and PDU2 format is used, the PS-field
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of the PGN shall be set to zero. The Destination Address shall be set
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elsewhere.
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@ -96,15 +96,15 @@ Addressing
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Both static and dynamic addressing methods can be used.
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For static addresses, no extra checks are made by the kernel, and provided
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For static addresses, no extra checks are made by the kernel and provided
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addresses are considered right. This responsibility is for the OEM or system
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integrator.
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For dynamic addressing, so-called Address Claiming, extra support is foreseen
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in the kernel. In J1939 any ECU is known by it's 64-bit NAME. At the moment of
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in the kernel. In J1939 any ECU is known by its 64-bit NAME. At the moment of
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a successful address claim, the kernel keeps track of both NAME and source
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address being claimed. This serves as a base for filter schemes. By default,
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packets with a destination that is not locally, will be rejected.
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packets with a destination that is not locally will be rejected.
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Mixed mode packets (from a static to a dynamic address or vice versa) are
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allowed. The BSD sockets define separate API calls for getting/setting the
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@ -153,8 +153,8 @@ described below.
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In order to send data, a bind(2) must have been successful. bind(2) assigns a
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local address to a socket.
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Different from CAN is that the payload data is just the data that get send,
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without it's header info. The header info is derived from the sockaddr supplied
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Different from CAN is that the payload data is just the data that get sends,
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without its header info. The header info is derived from the sockaddr supplied
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to bind(2), connect(2), sendto(2) and recvfrom(2). A write(2) with size 4 will
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result in a packet with 4 bytes.
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@ -191,7 +191,7 @@ can_addr.j1939.addr contains the address.
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The bind(2) system call assigns the local address, i.e. the source address when
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sending packages. If a PGN during bind(2) is set, it's used as a RX filter.
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I.e. only packets with a matching PGN are received. If an ADDR or NAME is set
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I.e. only packets with a matching PGN are received. If an ADDR or NAME is set
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it is used as a receive filter, too. It will match the destination NAME or ADDR
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of the incoming packet. The NAME filter will work only if appropriate Address
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Claiming for this name was done on the CAN bus and registered/cached by the
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