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hid_mapping_format

Proposed HID Controller Mapping File Format

This specification is for a future feature (not currently implemented) and is in discussion. Details may change before the specification is finalized.

Introduction

Support for additional HID controllers can be added to Mixxx by creating a new “mapping” file. This file tells Mixxx how to translate data bytes from a controller into commands that Mixxx will understand (by mapping the bytes onto MixxxControls or script functions.)

The mapping files are located in the following paths:

  • Windows: C:\Program Files\Mixxx\controllers
  • Linux: /usr/share/mixxx/controllers (or /usr/local/share/mixxx/controllers)
  • OS X: /Applications/Mixxx.app/Contents/Resources/controllers

By far, the easiest way to create a new mapping is by copying and modifying any of the XML files that ship with Mixxx using the information on this page. When you've finished creating your mapping, please send it to us and we'll include it in Mixxx.

Sniffing your controller

If you don't have the HID spec for your controller, first check the manufacturer's web site under Support. Look for Manuals or User Guides. HID specs may appear in an appendix at the back of the manual. Failing that, you can usually sniff the data the controller sends with the following procedure:

  1. Start Mixxx (1.11.0 and later) from a command prompt using the –controllerDebug option like so:
    • Linux:
      [email protected]:~$ mixxx --controllerDebug
    • Windows: (v1.7.0 and later)
      C:\Program Files\Mixxx>mixxx --controllerDebug
    • Mac OSX:
      $ open -a mixxx --args --controllerDebug
  2. Look at the output
    • Watch the console output or look at the Mixxx.log file which will contain all of the HID byte packets Mixxx receives. As you manipulate the controller, the packets it sends will be printed to the screen/logged to the file. Compare subsequent packets to discover which button/slider/control affects what bit(s)/byte(s) (and the endianness if multiple bytes are affected.)
    • FIXME Add example here
  3. Add the byte offset, bit offset, length and endianness values to a <control> block in the XML file. This is detailed in the next section.

File Format

Mixxx uses a well-defined XML format to store its HID mappings. Details are embedded in the XML example below.

The first part of the file defines the version of the mapping (for future compatibility, as Mixxx abilities become more complex) and an optional info tag which contains information about the preset (primarily used for distribution of presets.)

<?xml version="1.0" encoding="utf-8"?>
    <MixxxControllerPreset schemaVersion="0.1" mixxxVersion="1.11.0"> <!-- Schema version number to help compatibility, should the format change -->
	<info><!-- Optional - information about the preset file -->
		<name>Example HID mapping for Mixxx</name>
		<author>Sean M. Pappalardo</author>
		<description>This is an example XML HID preset for Mixxx. This description is intended for distribution and could include comments about the extent of the functionality.</description>
	</info>

Controller definition

The core part of the file contains a definition for a single controller. There may be multiple controllers in one file (for more complex setups).

	<controller id="controller name" type="HID"> <!-- Many controllers in one file supported. A controller should only appear once. -->

The “controller id” is the brand & model of the controller, e.g. “EKS Otus”.

Controls section

	  <controls> <!-- One control group -->
	    <control> <!-- Several controls -->

If your controller can send different types of messages, you can specify which type this <controls> block interprets using the following format:

	  <controls byteoffset=0 value=0x01> <!-- Optional format that specifies what value the specified byte must have in order to use this block to interpret the packet. -->
	    <control>

or this:

	  <controls length=14> <!-- Optional format that specifies how many bytes the packet must be in order to use this block to interpret the packet. -->
	    <control>

MixxxControl

Group and key define the part of Mixxx that you want to affect. For a list of what these values can be, see the MixxxControls page.

	      <group>[Master]</group>
	      <key>crossfader</key>

Controller control

Use one of the following examples to map the above MixxxControl to a physical control (knob, button, switch, pad, etc.)

Single-byte controls

Many controls are represented by a single byte. Here is how to define one in the XML.

	      <byteoffset>1</byteoffset> <!-- Offset from the first byte in the packet. So 1 points to the second byte in the packet. -->
	      <length>1</length> <!-- Optional - Number of bytes that this control affects. The default is 1. -->
	      <min>0x00</min> <!-- Optional - Lowest value of this byte when the control is at its minimum setting. The default is 0x00. -->
	      <max>0xFF</max> <!-- Optional - Highest value of this byte when the control is at its maximum setting. The default is 0xFF. -->
Multiple-byte controls

Many controls are represented by multiple bytes. Here is how to define such a control in the XML.

	      <byteoffset>2</byteoffset> <!-- Offset from the first byte in the packet, regardless of endianness. So 2 points to the third byte in the packet. -->
	      <length>2</length> <!-- Number of bytes that this control affects. -->
	      <endian>little</endian> <!-- Optional - Little endian means the most significant byte is the last one (second in this case.) "little" is the default. -->
	      <min>0x0000</min> <!-- Optional - Lowest value of these bytes when the control is at its minimum setting (always big-endian for readability.) 0 is the default. -->
	      <max>0x01FF</max> <!-- Optional - Highest value of these bytes when the control is at its maximum setting (always big-endian for readability.) 0xFFFF is the default for two bytes. -->
Bit-level controls

Some controls are represented by individual bits (typically the case for buttons.) Here is how to define them in the XML.

	      <byteoffset>4</byteoffset> <!-- Offset from the first byte in the packet. So 4 points to the third byte in the packet. -->
	      <bit>6</bit> <!-- Bit number in the byte (8 bits.) Bit 1 is the rightmost one, bit 8 is the leftmost (high) bit. -->
	      <length>1</length> <!-- Optional - Number of bits that make up this control. A single-bit value is either on or off. 1 bit is the default. -->

Question: Should the bit number above be changed to a bit offset from the leftmost one so it matches the byte offset convention?

Proposal from Hile: If the control represents multiple bits in one byte, following format could be used to shorten the XML format mapping bits to groups and keys. This is alternative format to above specified <bit> controls.

Note that a bitmap differs from other controls, because with it, group and key are inside bit elements, not as direct child nodes of control element.

              <control>
              <bitmap byteoffset="4" length="16">
                  <!-- byteoffset: Offset from the first byte in the packet. So 4 points to the third byte in the packet. -->
                  <!-- length: Number of bits that make up this control. A single-bit value is either on or off. 1 bit is the default. -->
              <bit offset="0"><group>[Channel1]</group><key>play</key></bit>
              <bit offset="5"><group>[Channel1]</group><key>cue</key></bit>
              <bit offset="15"><group>[Channel1]</group><key>reverse</key></bit>
              <!-- Bits not specified with <bit> here are ignored: you can define length 16 bitmap but only specify three bits like here -->
              </bitmap>
              </control>

Finish up

Close each <control> block with the following code:

	    </control>

…and the <controls> block with the following (after all of the <control> blocks):

	  </controls>

Finish up

Close the <controller> block with the following code:

	</controller>

…and the whole preset block with the following:

     </MixxxControllerPreset>
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hid_mapping_format.txt · Last modified: 2016/05/02 14:11 by pegasus