HOW TO IMPLEMENT IN CALLBACK FOR CUSTOM CLASS

Using MDK-PRO, 4.74 (actually 5, with legacy pack). I am trying to make a custom generic BULK class. I followed the suggestions for implementing a custom OUT Pipe and it is working fine.
For my IN pipe I am having partial success.

Does anyone know what callback or function I need to overload so that I can get a callback or an event flag to tell my code to write a buffer with USBD_WriteEP()?

I have tried making a simple class overload task like:

__task void USBD_RTX_EndPoint1 (void){
    volatile U16 evt;

    for (;;) {
        os_evt_wait_or(0xFFFF, 0xFFFF);         /* Wait for an Event */
        evt = os_evt_get();                     /* Get Event Flags */

        CLS_BulkIn ();                      /* data to send to Host */
        evt &= ~USB_EVT_IN;
        os_evt_clr(USB_EVT_IN,USBD_RTX_EPTask[2]);
    }
}

void CLS_BulkIn()
{
 ..process data to make buffer to send...
 USBD_WriteEP(0x81,thebuffer,thecount);
}

but to no avail, this never gets an event. If I push data into the endpoint blindly, then the host will pick it up, however, I am trying to push data in response to an IN phase on the bus.
Hopefully,
-Steve