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.
 
 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
 
 
 Known limitations of the controller