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.