## MMPM/2 Device Driver Reference

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### VSD_RESOURCE - Remarks

When an audio device driver is installed in MMPM/2, the installation routines place the following three keywords in the MMPM2.INI file:

RESOURCEUNITS=

RESOURCECLASS=

VALIDCOMBINATIONS=

Because MMPM/2 allows many applications to simultaneously open the audio card, it uses these keywords to determine which applications can simultaneously use the audio device. All of the numbers are arbitrary and are defined on a device-by-device basis. However, device driver writers should use the numbering scheme defined below:

The keyword RESOURCECLASSES indicates the different resource types available on the audio device. The first parameter is the number of classes and it is followed by a listing of classes. A vendor should provide a class for each data type that they support. For instance, if the XYZ audio card can only play PCM files, it would only have one resource class - the PCM class. However, if the ABC audio card can play PCM, MIDI, and ADPCM, then it would have three classes. The VSD should fill in the ulClass field with the class that is appropriate for this mode.

The keyword RESOURCEUNITS indicates the maximum number of instances that can be active on the card at any particular time. For example, if the XYZ card mentioned above had the ability to play three PCM files at the same time, the RESOURCEUNITS for this card would be three. In contrast, the ABC card can only play one PCM file and one MIDI file at any one time. Therefore, its resource units should be two. The VSD should fill in the ulResUnits field with the correct number of resources for the current mode (typically, one).