Application writers can create their own effects by creating a custom force. A custom force is an array of constant force values played back by the device.
The type-specific structure for custom waveform effects is DICUSTOMFORCE.
You should set the dwSamplePeriod member of the DICUSTOMFORCE structure and the dwSamplePeriod member of the DIEFFECT structure to the same value. This is the length of time, in milliseconds, for which each element in the array of forces will be played.
The custom force is played repeatedly until the time set in the dwDuration member of the DIEFFECT structure has elapsed.