audio.device/ADCMD_FREE

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 NAME
 ADCMD_FREE -- free audio channels for allocation
 FUNCTION
 ADCMD_FREE is a command for multiple audio channels. For each
 selected channel (io_Unit), if the allocation key (ioa_AllocKey) is
 correct, ADCMD_FREE does the following:
 . restores the channel to a known state (CMD_RESET),
 . changes the channels allocation key, and
 . makes the channel available for re-allocation.
 . If the channel is locked (ADCMD_LOCK) ADCMD_FREE unlocks it and
 clears the bit for the channel (io_Unit) in the lock I/O request.
 If the lock I/O request has no channel bits set ADCMD_FREE replies
 the lock I/O request, and
 . checks if there are allocation requests (ADCMD_ALLOCATE) waiting
 for the channel.
 Otherwise, ADCMD_FREE returns an error (ADIOERR_NOALLOCATION).
 ADCMD_FREE is synchronous and only replies (mn_ReplyPort) if the quick
 flag (IOF_QUICK) is clear. Do not use ADCMD_FREE in interrupt code.
 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 free (bits 0 thru 3 correspond to
 channels 0 thru 3)
 io_Command - command number for ADCMD_FREE
 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 successfully freed (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

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