-Linux SocketCAN driver for ELM327
-==================================
+.. SPDX-License-Identifier: (GPL-2.0-only OR BSD-3-Clause)
+
+can327: ELM327 driver for Linux SocketCAN
+==========================================
+
+Out-of-tree version
+--------------------
+
+This is the non-upstreamed version of the can327 driver.
+Please see out-of-tree.rst for compilation/usage hints.
+
+
Authors
--------
Motivation
-----------
-CAN adapters are expensive, few, and far between.
-ELM327 interfaces are cheap and plentiful.
-
This driver aims to lower the initial cost for hackers interested in
working with CAN buses.
+CAN adapters are expensive, few, and far between.
+ELM327 interfaces are cheap and plentiful.
+Let's use ELM327s as CAN adapters.
+
Introduction
-------------
This driver is an effort to turn abundant ELM327 based OBD interfaces
-into full-fledged (as far as possible) CAN interfaces.
+into full fledged (as far as possible) CAN interfaces.
-Since the ELM327 was never meant to be a stand-alone CAN controller,
+Since the ELM327 was never meant to be a stand alone CAN controller,
the driver has to switch between its modes as quickly as possible in
-order to approximate full-duplex operation.
+order to fake full-duplex operation.
-As such, elmcan is a best-effort driver. However, this is more than
+As such, can327 is a best effort driver. However, this is more than
enough to implement simple request-response protocols (such as OBD II),
and to monitor broadcast messages on a bus (such as in a vehicle).
-Requirements
--------------
-
-This requires Linux 4.11 (for 431af779256c), and has been tested on 4.19.
-
-Also, elmcan depends on ``can-dev``:
-
- sudo modprobe can-dev
-
-
-
Data sheet
-----------
------------------------------------
Use a terminal program to attach to the controller.
+The default settings are 38400 baud/s, 8 data bits, no parity, 1 stopbit.
After issuing the "``AT WS``" command, the controller will respond with
its version::
>
+Note that clones may claim to be any version they like.
+It is not indicative of their actual feature set.
+
How to attach the line discipline
To change the ELM327's serial settings, please refer to its data
sheet. This needs to be done before attaching the line discipline.
+Once the ldisc is attached, the CAN interface starts out unconfigured.
+Set the speed before starting it:
+ # The interface needs to be down to change parameters
+ sudo ip link set can0 down
+ sudo ip link set can0 type can bitrate 500000
+ sudo ip link set can0 up
-Module parameters
-------------------
-
-- ``accept_flaky_uart`` - Try to live with a bad controller or UART line
-
- Some adapters and/or their connection are unreliable. Enable this
- option to try and work around the situation. This is a best-effort
- workaround, so undefined behavior will likely occur sooner or later.
+500000 bit/s is a common rate for OBD-II diagnostics.
+If you're connecting straight to a car's OBD port, this is the speed
+that most cars (but not all!) expect.
- LOAD TIME::
-
- module/kernel parameter: accept_flaky_uart=[0|1]
+After this, you can set out as usual with candump, cansniffer, etc.
Known limitations of the controller
------------------------------------
-- Clone "v1.5" devices
+- Clone devices ("v1.5" and others)
Sending RTR frames is not supported and will be dropped silently.
sending a frame, the ELM327 will be in "receive reply" mode, in
which it *does* ACK any received frames. Once the bus goes silent
or an error occurs (such as BUFFER FULL), the ELM327 will end reply
- reception mode on its own and elmcan will fall back to "``AT MA``"
+ reception mode on its own and can327 will fall back to "``AT MA``"
in order to keep monitoring the bus.
- All versions
- No automatic full duplex operation is supported. The driver will
- switch between input/output mode as quickly as possible.
+ No full duplex operation is supported. The driver will switch
+ between input/output mode as quickly as possible.
The length of outgoing RTR frames cannot be set. In fact, some
clones (tested with one identifying as "``v1.5``") are unable to
- Versions prior to 1.3
- These chips cannot be used at all with elmcan. They do not support
- the "``AT D1``", which is necessary to avoid parsing conflicts on
- incoming data, as well as distinction of RTR frame lengths.
+ These chips cannot be used at all with can327. They do not support
+ the "``AT D1``" command, which is necessary to avoid parsing conflicts
+ on incoming data, as well as distinction of RTR frame lengths.
Specifically, this allows for easy distinction of SFF and EFF
frames, and to check whether frames are complete. While it is possible
The init script in the driver switches off several configuration options
that are only meaningful in the original OBD scenario the chip is meant
-for, and are actually a hindrance for elmcan.
+for, and are actually a hindrance for can327.
When a command is not recognized, such as by an older version of the
?
>
-At present, elmcan does not evaluate this response and silently assumes
+At present, can327 does not evaluate this response and silently assumes
that all commands are recognized. It is structured such that it will
degrade gracefully when a command is unknown. See the sections above on
known limitations for details.
123 8 DEADBEEF12345678
For 29 bit CAN frames, the address format is slightly different, which
-elmcan uses to tell the two apart::
+can327 uses to tell the two apart::
12 34 56 78 8 DEADBEEF12345678
If communications don't work with the adapter connected, check for the
termination resistors on its PCB and try removing them.
-
-
-
-To Do list for future development
-----------------------------------
-
-- DMA capable rx/tx buffers
- (is this relevant for this driver?)
-
-- flushing of ``tx_work`` is too late in ``ldisc_close()``
- (is this still the case?)
projects / elmcan.git / blobdiff