Control plugins extends functionality and features of control devices. The plugins take care about various control mapping or so.

The child configuration (in one compound):

ctl.test {
    type remap
    child "hw:0"
    ... map/remap configuration ...
}

The child may be defined as compound containing the full specification:

ctl.test {
    type remap
    child {
        type hw
        card 0
    }
    ... map/remap configuration ...
}

Plugin: hw

This plugin communicates directly with the ALSA kernel driver. It is a raw communication without any conversions.

control.name {
    type hw         # Kernel PCM
    card INT/STR        # Card name (string) or number (integer)
}

Function reference

Plugin: Remap & map

This plugin can remap (rename) identifiers (except the numid part) for a child control to another. The plugin can also merge the multiple child controls to one or split one control to more.

ctl.name {
    type remap              # Remap controls
    child STR               # Child name
    # or
    child {                 # Child definition
        type STR
        ...
    }
    remap {
        # the ID strings are parsed in the amixer style like 'name="Headphone Playback Switch",index=2'
        SRC_ID1_STR DST_ID1_STR
        SRC_ID2_STR DST_ID2_STR
        ...
    }
    map {
        # join two stereo controls to one
        CREATE_ID1_STR {
            SRC_ID1_STR {
                vindex.0 0  # source channel 0 to merged channel 0
                vindex.1 1
            }
            SRC_ID2_STR {
                vindex.2 0
                vindex.3 1  # source channel 1 to merged channel 3
            }
        }
        # split stereo to mono
        CREATE_ID2_STR {
            SRC_ID3_STR {
                vindex.0 0  # stereo to mono (first channel)
            }
        }
        CREATE_ID3_STR {
            SRC_ID4_STR {
                vindex.0 1  # stereo to mono (second channel)
            }
        }
        # join two stereo to one stereo (minimum value is returned for read operation)
        CREATE_ID4_STR {
            SRC_ID5_STR.vindex.0 [ 0 1 ] # source channels 0+1 to merged channel 0
            SRC_ID6_STR.vindex.1 [ 0 1 ] # source channels 0+1 to merged channel 1
        }
    }
    sync {
        # synchronize multiple controls without any translations
        sample_group_1 [
            SYNC_ID1_STR
            SYNC_ID2_STR
        ]
        # synchronize multiple controls without any translations
        # add functionality on/off switch
        sample_group_2 {
            switch SYNC_SWITCH_ID
            controls [
                SYNC_ID3_STR
                SYNC_ID4_STR
            ]
        }
    }
}