NAME
    TD_MOTOR/ETD_MOTOR -- control the on/off state of a drive motor.

FUNCTION
    This command gives control over the disk motor. The motor may be
    turned on or off. When it is on, the drive light automatically turns
    on as well.

    If the motor is just being turned on, the device will delay the
    proper amount of time to allow the drive to come up to speed. Normally,
    turning the drive on is not necessary, the device does this
    automatically if it receives a request when the motor is off. However,
    turning the motor off is the programmer's responsibility.

    In addition, the standard instructions to the user are that it is safe
    to remove a disk from a drive if and only if the motor is off (that is,
    if the disk light is off).

IO REQUEST INPUT
    io_Device       preset by the call to opendevice()
    io_Unit         preset by the call to opendevice()
    io_Command      TD_MOTOR or ETD_MOTOR
    io_Flags        0 or IOF_QUICK
    io_Length       the requested state of the motor, 0 to turn the motor
                    off, and 1 to turn the motor on.
    iotd_Count      (ETD_MOTOR only) maximum allowable change counter
                    value.

IO REQUEST RESULT
    io_Error  - 0 for success, or an error code as defined in
                <devices/trackdisk.h>
    io_Actual - if io_Error is 0 this contains the previous state of the
                drive motor.