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
into full-fledged (as far as possible) CAN interfaces.
Since the ELM327 was never meant to be a stand-alone CAN controller,
-the driver has to switch between its modes asa quickly as possible in
-order to approximate full-duplex operation.
+the driver has to switch between its modes as quickly as possible in
+order to fake full-duplex operation.
As such, elmcan is a best-effort driver. However, this is more than
enough to implement simple request-response protocols (such as OBD II),
+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
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.
+ Without this option, the driver will bail on the first unrecognized
+ character it receives from the TTY.
LOAD TIME::
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.
- 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
+A note on CAN bus termination
+------------------------------
+
+Your adapter may have resistors soldered in which are meant to terminate
+the bus. This is correct when it is plugged into a OBD-II socket, but
+not helpful when trying to tap into the middle of an existing CAN bus.
+
+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
-
-- flushing of ``tx_work`` is too late in ``ldisc_close()``
+- None currently