For a description of the error return values from DriverProc, see the discussion of installable drivers in the documentation for the Microsoft Windows Software Development Kit. The following table lists the general error return values from auxMessage, wodMessage, widMessage, midMessage, and midMessage.
MMSYSERR_NOERROR
No error.
MMSYSERR_ERROR
Unspecified error.
MMSYSERR_NOTENABLED
Driver is not enabled.
MMSYSERR_ALLOCATED
Requested device is already allocated.
MMSYSERR_NOMEM
Memory allocation error.
MMSYSERR_NOTSUPPORTED
Driver does not support specified operation.
In addition to these general error return values, there are error return values unique to each type of audio device. The following table lists these device-specific error return values.
MIDIERR_UNPREPARED
MIDI data block has not been prepared.
MIDIERR_NOTREADY
MIDI output hardware is busy.
MIDIERR_STILLPLAYING
Driver is still playing MIDI data.
WAVERR_BADFORMAT
Unsupported waveform data format.
WAVERR_STILLPLAYING
Driver is still playing waveform data.
WAVERR_UNPREPARED
Specified waveform data block has not been prepared.