Fix evdev relative axes, add detect option

1 files changed, 12 insertions, 6 deletions

diff --git a/backends/evdev.md b/backends/evdev.md
index d750f1e..995b44c 100644
--- a/backends/evdev.md
+++ b/backends/evdev.md
@@ -7,7 +7,9 @@ This functionality may require elevated privileges (such as special group member
 
 #### Global configuration
 
-This backend does not take any global configuration.
+| Option        | Example value         | Default value         | Description           |
+|---------------|-----------------------|-----------------------|-----------------------|
+| `detect`      | `on`                  | `off`                 | Output the channel specification for all events coming in on configured instances to help with configuration. |
 
 #### Instance configuration
 
@@ -18,7 +20,8 @@ This backend does not take any global configuration.
 | `output`	| `My Input Device`	| none		| Output device presentation name. Setting this option enables the instance for output	|
 | `exclusive`	| `1`			| `0`		| Prevent other processes from using the device		|
 | `id`		| `0x1 0x2 0x3`		| none		| Set output device bus identification (Vendor, Product and Version), optional |
-| `axis.AXISNAME`| `34300 0 65536 255 4095` | none	| Specify absolute axis details (see below) for output. This is required for any absolute axis to be output.
+| `axis.AXISNAME`| `34300 0 65536 255 4095` | none	| Specify absolute axis details (see below) for output. This is required for any absolute axis to be output. | 
+| `relaxis.AXISNAME`| `65534 32767` | none	| Specify relative axis details (extent and optional initial value) for output and input (see below). |
 
 The absolute axis details configuration (e.g. `axis.ABS_X`) is required for any absolute axis on output-enabled
 instances. The configuration value contains, space-separated, the following values:
@@ -34,6 +37,13 @@ If an axis is not used for output, this configuration can be omitted.
 
 For real devices, all of these parameters for every axis can be found by running `evtest` on the device.
 
+To use the input from relative axes in absolute-value based protocols, the backend needs a reference frame to
+convert the relative movements to absolute values.
+
+If relative axes are used without specifying their extents, the channel will generate normalized values
+of `0`, `0.5` and `1` for any input less than, equal to and greater than `0`, respectively. As for output, only
+the values `-1`, `0` and `1` are generated for the same interval.
+
 #### Channel specification
 
 A channel is specified by its event type and event code, separated by `.`. For a complete list of event types and codes
@@ -64,10 +74,6 @@ Input devices may synchronize logically connected event types (for example, X an
 events. The MIDIMonster also generates these events after processing channel events, but may not keep the original
 event grouping.
 
-Relative axes (`EV_REL`-type events), such as generated by mouses, are currently handled in a very basic fashion,
-generating only the normalized channel values of `0`, `0.5` and `1` for any input less than, equal to and greater
-than `0`, respectively. As for output, only the values `-1`, `0` and `1` are generated for the same interval.
-
 `EV_KEY` key-down events are sent for normalized channel values over `0.9`.
 
 Extended event type values such as `EV_LED`, `EV_SND`, etc are recognized in the MIDIMonster configuration file