CCS/TMS320F28069F: Question on usb_dev_bulk example, how can I tx data to Txbuffer only after device gets request from host

Tool/software: Code Composer Studio

Looks like the usb_dev_bulk example put the data into TxBuffer once it receives a character by calling EchoNewDataToHost().

If I understand right, can I do it in a different way, which is, the device only puts data into TxBuffer when host requests it?
Is there a related EVENT can be put into TxHandler like this?

uint32_t
TxHandler(void *pvCBData, uint32_t ulEvent, uint32_t ulMsgValue,
void *pvMsgData)
{
//
// No action is required in response to any transmit event in this example.
// All that is done is to update the transmit counter.
//
if(ulEvent == USB_EVENT_TX_COMPLETE)
{
g_ulTxCount += ulMsgValue;
}

return(0);
}

uint32_t
TxHandler(void *pvCBData, uint32_t ulEvent, uint32_t ulMsgValue,
          void *pvMsgData)
{
    switch(ulEvent)
    //
    // No action is required in response to any transmit event in this example.
    // All that is done is to update the transmit counter.
    //
    case USB_EVENT_TX_COMPLETE:
    {
        g_ulTxCount += ulMsgValue;
        break;
    }
    //

    case USB_EVENT_TX_REQUEST:
    {
        usbdatatx();
        break;
    }

    return(0);
}

Thanks in advance