NAME
       ADCMD_SETPREC -- set the allocation precedence for audio channels

   FUNCTION
       ADCMD_SETPREC is a command for multiple audio channels.  For each
       selected channel (io_Unit), if the allocation key (ioa_AllocKey) is
       correct, ADCMD_SETPREC sets the allocation precedence to a new value
       (ln_Pri) and checks if there are allocation requests (ADCMD_ALLOCATE)
       waiting for the channel which now have higher precedence; otherwise,
       ADCMD_SETPREC returns an error (ADIOERR_NOALLOCATION).  ADCMD_SETPREC
       is synchronous and only replies (mn_ReplyPort) if the quick flag
       (IOF_QUICK) is clear.  Do not use ADCMD_SETPREC in interrupt code.

   INPUTS
       ln_Pri      - new allocation precedence (-128 thru 127)
       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 set precedence (bits 0 thru 3
                     correspond to channels 0 thru 3)
       io_Command  - command number for ADCMD_SETPREC
       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 that successfully set precedence
                     (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