readme.rst: Add hint on upping the interface before use

Also name 500kbit/s as the most common OBD-II speed, to save newcomers
some headache.

diff --git a/readme.rst b/readme.rst
index 4103d18ce0db158c9842f435b9ae1944fbe83b8a..e3792211b6c172ae506f7f073b0517e715250bec 100644 (file)
--- a/readme.rst
+++ b/readme.rst
@@ -105,6 +105,20 @@ The line discipline can be attached on a command prompt as follows::
 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
+
+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.
+
+After this, you can set out as usual with candump, cansniffer, etc.
+
 
 
 Known limitations of the controller