NAME
       CMD_RESET -- restore device to a known state

   FUNCTION
       CMD_RESET is a standard command for multiple audio channels.  For each
       selected channel (io_Unit), if the allocation key (ioa_AllocKey) is
       correct, CMD_RESET:
         . clears the hardware audio registers and attach bits,
         . sets the audio interrupt vector,
         . cancels all pending I/O (CMD_FLUSH), and
         . un-stops the channel if it is stopped (CMD_STOP),

       Otherwise, CMD_RESET returns an error (ADIOERR_NOALLOCATION).
       CMD_RESET is synchronous and only replies (mn_ReplyPort) if the quick
       flag (IOF_QUICK) is clear.  Do not use CMD_RESET in interrupt code at
       interrupt level 5 or higher.

   INPUTS
       mn_ReplyPort- pointer to message port that receives I/O request
                     if the quick flag (IOF_QUICK) is clear
       io_Device   - pointer to device node, must be set by (or copied from
                     I/O block set by) OpenDevice function
       io_Unit     - bit map of channels to reset (bits 0 thru 3 correspond
                     to channels 0 thru 3)
       io_Command  - command number for CMD_RESET
       io_Flags    - flags, must be cleared if not used:
                     IOF_QUICK - (CLEAR) reply I/O request
       ioa_AllocKey- allocation key, must be set by (or copied from I/O block
                     set by) OpenDevice function or ADCMD_ALLOCATE command

   OUTPUTS
       io_Unit     - bit map of channels to successfully reset (bits 0 thru 3
                     correspond to channels 0 thru 3)
       io_Error    - error number:
                     0                    - no error
                     ADIOERR_NOALLOCATION - allocation key (ioa_AllocKey)
                                            does not match key for channel