Enable sound on C-Media CM6206 in FreeBSD

#!/usr/bin/env bash
# For instructions look at:
# https://lists.freebsd.org/pipermail/freebsd-current/2015-April/055563.html
#set -xu
declare -r USB_REQ_SET_CONFIGURATION=0x09
declare -r USB_DIR_OUT=0    # to device
declare -r USB_DIR_IN=0x80  # to host
declare -r USB_TYPE_CLASS=2#100000  # (0x01<<5)
declare -r USB_RECIP_ENDPOINT=0x02

##################################################################
# Purpose:
#       C-Media CM106/CM106+ have four 16-bit internal registers that
#       are nicely documented in the device's data sheet.
# Arguments:
#       $1 -> USB device in the X.Y form
#       $2 -> register number
#       $3 -> register value
# Return: usbconfig status
##################################################################
snd_usb_cm106_write_int_reg(){
    local usb_dev="$1"
    local int_reg="$2"
    local u16_value="$3"
    local p1=$(($USB_DIR_OUT | $USB_TYPE_CLASS | $USB_RECIP_ENDPOINT))
    local p2=$(($u16_value & 0xFF))
    local p3=$((($u16_value >> 8) & 0xff))
    usbconfig -d "$usb_dev" do_request "$p1" \
        "$USB_REQ_SET_CONFIGURATION" 0 0 4 0x20 "$p2" "$p3" "$int_reg"
}

##################################################################
# Purpose:
#       Enable line-out driver mode, set headphone source to front
#       channels, enable stereo mic.
# Arguments:
#       $1 -> USB device in the X.Y form
# Return: usbconfig status
##################################################################
snd_usb_cm106_boot_quirk() {
    local usb_dev="$1"
    snd_usb_cm106_write_int_reg "$usb_dev" 2 0x8004
}

##################################################################
# Purpose:
#       C-Media CM6206 is based on CM106 with two additional
#       registers that are not documented in the data sheet.
#       Values here are chosen based on sniffing USB traffic
#       under Windows.
# Arguments:
#       $1 -> USB device in the <unit>.<addr> form
# Return: usbconfig status
##################################################################
snd_usb_cm6206_boot_quirk() {
    local usb_dev="$1"
    local val=(0x2004 0x3000 0xf800 0x143f 0x0000 0x3000)
    for ((reg = 0 ; reg < ${#val[@]} ; reg++)); do
        echo "Writing register $reg"
        snd_usb_cm106_write_int_reg $usb_dev $reg ${val[$reg]}
    done
}

if [ $# -ne 1 ] ; then
    echo "Usage: $0 X.Y"
    echo "Argument:"
    echo "X.Y: USB device in the <unit>.<addr> form"
    exit 1
fi
snd_usb_cm6206_boot_quirk "$1"
#set +xu